Full Committee Hearing - "Climate Change Science and Economics"
Note: Due to time constraints, Panel 2 has been postponed and rescheduled for September 20th at 10:00 a.m.
Witness Panel 1
-
Dr. Ralph Cicerone
Witness Panel 1
Dr. Ralph Cicerone
CURRENT STATE OF CLIMATE SCIENCE:
RECENT STUDIES FROM THE NATIONAL ACADEMIESStatement of Ralph J. Cicerone, Ph.D.
President, National Academy of Sciences
before the
Committee on Energy and Natural Resources
United State Senate
July 21, 2005
Good morning, Mr. Chairman and members of the Committee. My name is Ralph Cicerone, and I am President of the National Academy of Sciences. Prior to this position, I served as Chancellor of the University of California at Irvine, where I also held the Daniel G. Aldrich Chair in Earth System Science. In addition, in 2001 I chaired the National Academies committee that wrote the report, Climate Change Science: An Analysis of Some Key Questions, at the request of the White House.This morning I will summarize briefly the current state of scientific understanding on climate change, based largely on the findings and recommendations in recent National Academies’ reports. These reports are the products of a study process that brings together leading scientists, engineers, public health officials and other experts to provide consensus advice to the nation on specific scientific and technical questions.
The Earth is warming. Weather station records and ship-based observations indicate that global mean surface air temperature increased about 0.7oF (0.4oC) since the early 1970’s (See Figure). Although the magnitude of warming varies locally, the warming trend is spatially widespread and is consistent with an array of other evidence (including melting glaciers and ice caps, sea level rise, extended growing seasons, and changes in the geographical distributions of plant and animal species). The ocean, which represents the largest reservoir of heat in the climate system, has warmed by about 0.12oF (0.06oC) averaged over the layer extending from the surface down to 750 feet, since 1993. Recent studies have shown that the observed heat storage in the oceans is consistent with expected impacts of a human-enhanced greenhouse effect.
The observed warming has not proceeded at a uniform rate. Virtually all the 20th century warming in global surface air temperature occurred between the early 1900s and the 1940s and from the 1970s until today, with a slight cooling of the Northern Hemisphere during the interim decades. The causes of these irregularities and the disparities in the timing are not completely understood, but the warming trend in global-average surface temperature observations during the past 30 years is undoubtedly real and is substantially greater than the average rate of warming during the twentieth century.
Laboratory measurements of gases trapped in dated ice cores have shown that for hundreds of thousands of years, changes in temperature have closely tracked atmospheric carbon dioxide concentrations. Burning fossil fuel for energy, industrial processes, and transportation releases carbon dioxide to the atmosphere. Carbon dioxide in the atmosphere is now at its highest level in 400,000 years and continues to rise.
Nearly all climate scientists today believe that much of Earth’s current warming has been caused by increases in the amount of greenhouse gases in the atmosphere, mostly from the burning of fossil fuels. The degree of confidence in this conclusion is higher today than it was 10, or even 5 years ago, but uncertainties remain. As stated in the Academies 2001 report, “the changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.”
One area of debate has been the extent to which variations in the Sun might contribute to recent observed warming trends. The Sun’s total brightness has been measured by a series of satellite-based instruments for more than two complete 11-year solar cycles. Recent analyses of these measurements argue against any detectable long-term trend in the observed brightness to date. Thus, it is difficult to conclude that the Sun has been responsible for the warming observed over the past 25 years.
Carbon dioxide can remain in the atmosphere for many decades and major parts of the climate system respond slowly to changes in greenhouse gas concentrations. The slow response of the climate system to increasing greenhouse gases also means that changes and impacts will continue during the twenty-first century and beyond, even if emissions were to be stabilized or reduced in the near future.
Simulations of future climate change project that, by 2100, global surface temperatures will be from 2.5 to 10.4oF (1.4 to 5.8oC) above 1990 levels. Similar projections of temperature increases, based on rough calculations and nascent theory, were made in the Academies first report on climate change published in the late 1970s. Since then, significant advances in our knowledge of the climate system and our ability to model and observe it have yielded consistent estimates. Pinpointing the magnitude of future warming is hindered both by remaining gaps in understanding the science and by the fact that it is difficult to predict society’s future actions, particularly in the areas of population growth, economic growth, and energy use practices.
Other scientific uncertainties about future climate change relate to the regional effects of climate change and how climate change will affect the frequency and severity of weather events. Although scientists are starting to forecast regional weather impacts, the level of confidence is less than it is for global climate projections. In general, temperature is easier to predict than changes such as rainfall, storm patterns, and ecosystem impacts.
It is important to recognize however, that while future climate change and its impacts are inherently uncertain, they are far from unknown. The combined effects of ice melting and sea water expansion from ocean warming will likely cause the global average sea-level to rise by between 0.1 and 0.9 meters between 1990 and 2100. In colder climates, such warming could bring longer growing seasons and less severe winters. Those in coastal communities, many in developing nations, will experience increased flooding due to sea level rise and are likely to experience more severe storms and surges. In the Arctic regions, where temperatures have risen more than the global average, the landscape and ecosystems are being altered rapidly.
The task of mitigating and preparing for the impacts of climate change will require worldwide collaborative inputs from a wide range of experts, including natural scientists, engineers, social scientists, medical scientists, those in government at all levels, business leaders and economists. Although the scientific understanding of climate change has advanced significantly in the last several decades, there are still many unanswered questions. Society faces increasing pressure to decide how best to respond to climate change and associated global changes, and applied research in direct support of decision making is needed.
My written testimony describes the current state of scientific understanding of climate change in more detail, based largely on important findings and recommendations from a number of recent National Academies’ reports.
The Earth is warmingThe most striking evidence of a global warming trend are closely scrutinized data that show a relatively rapid increase in temperature, particularly over the past 30 years. Weather station records and ship-based observations indicate that global mean surface air temperature increased about 0.7oF (0.4oC) since the early 1970’s (See Figure). Although the magnitude of warming varies locally, the warming trend is spatially widespread and is consistent with an array of other evidence (e.g., melting glaciers and ice caps, sea level rise, extended growing seasons, and changes in the geographical distributions of plant and animal species).
Global annual-mean surface air temperature change derived from the meteorological station network. Data and plots available from the Goddard Institute for Space Sciences (GISS) at http://data.giss.nasa.gov/gistemp/graphs/.
The ocean, which represents the largest reservoir of heat in the climate system, has warmed by about 0.12oF (0.06oC) averaged over the layer extending from the surface down to 750 feet, since 1993. Recent studies have shown that the observed heat storage in the oceans is what would be expected by a human-enhanced greenhouse effect. Indeed, increased ocean heat content accounts for most of the planetary energy imbalance (i.e., when the Earth absorbs more energy from the Sun than it emits back to space) simulated by climate models with mid-range climate sensitivity.The observed warming has not proceeded at a uniform rate. Virtually all the 20th century warming in global surface air temperature occurred between the early 1900s and the 1940s and since the 1970s, with a slight cooling of the Northern Hemisphere during the interim decades. The troposphere warmed much more during the 1970s than during the two subsequent decades, whereas Earth’s surface warmed more during the past two decades than during the 1970s. The causes of these irregularities and the disparities in the timing are not completely understood.
A National Academies report released in 2000, Reconciling Observations of Global Temperature Change, examined different types of temperature measurements collected from 1979 to 1999 and concluded that the warming trend in global-average surface temperature observations during the previous 20 years is undoubtedly real and is substantially greater than the average rate of warming during the twentieth century. The report concludes that the lower atmosphere actually may have warmed much less rapidly than the surface from 1979 into the late 1990s, due both to natural causes (e.g., the sequence of volcanic eruptions that occurred within this particular 20-year period) and human activities (e.g., the cooling of the upper part of the troposphere resulting from ozone depletion in the stratosphere). The report spurred many research groups to do similar analyses. Satellite observations of middle troposphere temperatures, after several revisions of the data, now compare reasonably with observations from surface stations and radiosondes, although some uncertainties remain.
Humans have had an impact on climateLaboratory measurements of gases trapped in dated ice cores have shown that for hundreds of thousands of years, changes in temperature have closely tracked with atmospheric carbon dioxide concentrations. Burning fossil fuel for energy, industrial processes, and transportation releases carbon dioxide to the atmosphere. Carbon dioxide in the atmosphere is now at its highest level in 400,000 years and continues to rise. Nearly all climate scientists today believe that much of Earth’s current warming has been caused by increases in the amount of greenhouse gases in the atmosphere. The degree of confidence in this conclusion is higher today than it was 10, or even 5 years ago, but uncertainties remain. As stated in the Academies 2001 report, “the changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability.”
Carbon dioxide can remain in the atmosphere for many decades and major parts of the climate system respond slowly to changes in greenhouse gas concentrations. The slow response of the climate system to increasing greenhouse gases also means that changes and impacts will continue during the twenty-first century and beyond, even if emissions were to be stabilized or reduced in the near future.
In order to compare the contributions of the various agents that affect surface temperature, scientists have devised the concept of “radiative forcing.” Radiative forcing is the change in the balance between radiation (i.e., heat and energy) entering the atmosphere and radiation going back out. Positive radiative forcings (e.g., due to excess greenhouse gases) tend on average to warm the Earth, and negative radiative forcings (e.g., due to volcanic eruptions and many human-produced aerosols) on average tend to cool the Earth. The Academies recent report, Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005), takes a close look at how climate has been changed by a range of forcings. A key message from the report is that it is important to quantify how human and natural processes cause changes in climate variables other than temperature. For example, climate-driven changes in precipitation in certain regions could have significant impacts on water availability for agriculture, residential and industrial use, and recreation. Such regional impacts will be much more noticeable than projected changes in global average temperature of a degree or more.
One area of debate has been the extent to which variations in the Sun might contribute to recent observed warming trends. Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005) also summarizes current understanding about this issue. The Sun’s brightness—its total irradiance—has been measured continuously by a series of satellite-based instruments for more than two complete 11-year solar cycles. These multiple solar irradiance datasets have been combined into a composite time series of daily total solar irradiance from 1979 to the present. Different assumptions about radiometer performance lead to different reconstructions for the past two decades. Recent analyses of these measurements, taking into account instrument calibration offsets and drifts, argue against any detectable long-term trend in the observed irradiance to date. Likewise, models of total solar irradiance variability that account for the influences of solar activity features—dark sunspots and bright faculae—do not predict a secular change in the past two decades. Thus, it is difficult to conclude from either measurements or models that the Sun has been responsible for the warming observed over the past 25 years.
Knowledge of solar irradiance variations is rudimentary prior to the commencement of continuous space-based irradiance observations in 1979. Models of sunspot and facular influences developed from the contemporary database have been used to extrapolate daily variations during the 11-year cycle back to about 1950 using contemporary sunspot and facular proxies, and with less certainty annually to 1610. Circumstantial evidence from cosmogenic isotope proxies of solar activity (14C and 10Be) and plausible variations in Sun-like stars motivated an assumption of long-term secular irradiance trends, but recent work questions the evidence from both. Very recent studies of the long term evolution and transport of activity features using solar models suggest that secular solar irradiance variations may be limited in amplitude to about half the amplitude of the 11-year cycle.
Warming will continue, but its impacts are difficult to projectThe Intergovernmental Panel on Climate Change (IPCC), which involves hundreds of scientists in assessing the state of climate change science, has estimated that, by 2100, global surface temperatures will be from 2.5 to 10.4oF (1.4 to 5.8oC) above 1990 levels. Similar projections of temperature increases, based on rough calculations and nascent theory, were made in the Academies first report on climate change published in the late 1970s. Since then, significant advances in our knowledge of the climate system and our ability to model and observe it have yielded consistent estimates. Pinpointing the magnitude of future warming is hindered both by remaining gaps in understanding the science and by the fact that it is difficult to predict society’s future actions, particularly in the areas of population growth, economic growth, and energy use practices.
One of the major scientific uncertainties is how climate could be affected by what are known as “climate feedbacks.” Feedbacks can either amplify or dampen the climate response to an initial radiative forcing. During a feedback process, a change in one variable, such as carbon dioxide concentration, causes a change in temperature, which then causes a change in a third variable, such as water vapor, which in turn causes a further change in temperature. Understanding Climate Change Feedbacks (2003) looks at what is known and not known about climate change feedbacks and identifies important research avenues for improving our understanding.
Other scientific uncertainties relate to the regional effects of climate change and how climate change will affect the frequency and severity of weather events. Although scientists are starting to forecast regional weather impacts, the level of confidence is less than it is for global climate projections. In general, temperature is easier to predict than changes such as rainfall, storm patterns, and ecosystem impacts. It is very likely that increasing global temperatures will lead to higher maximum temperatures and fewer cold days over most land areas. Some scientists believe that heat waves such as those experienced in Chicago and central Europe in recent years will continue and possibly worsen. The larger and faster the changes in climate, the more difficult it will be for human and natural systems to adapt without adverse effects.
There is evidence that the climate has sometimes changed abruptly in the past—within a decade—and could do so again. Abrupt changes, for example the Dust Bowl drought of the 1930’s displaced hundreds of thousands of people in the American Great Plains, take place so rapidly that humans and ecosystems have difficulty adapting to it. Abrupt Climate Change: Inevitable Surprises (2002) outlines some of the evidence for and theories of abrupt change. One theory is that melting ice caps could “freshen” the water in the North Atlantic, shutting down the natural ocean circulation that brings warmer Gulf Stream waters to the north and cooler waters south again. This shutdown could make it much cooler in Northern Europe and warmer near the equator.
It is important to recognize that while future climate change and its impacts are inherently uncertain, they are far from unknown. The combined effects of ice melting and sea water expansion from ocean warming will likely cause the global average sea-level to rise by between 0.1 and 0.9 meters between 1990 and 2100. In colder climates, such warming could bring longer growing seasons and less severe winters. Those in coastal communities, many in developing nations, will experience increased flooding due to sea level rise and are likely to experience more severe storms and surges. In the Arctic regions, where temperatures have risen almost twice as much as the global average, the landscape and ecosystems are being altered rapidly.
Observations and data are the foundation of climate change scienceThere is nothing more valuable to scientists than the measurements and observations required to confirm or contradict hypotheses. In climate sciences, there is a peculiar relation between the scientist and the data. Whereas other scientific disciplines can run multiple, controlled experiments, climate scientists must rely on the one realization that nature provides. Climate change research requires observations of numerous characteristics of the Earth system over long periods of time on a global basis. Climate scientists must rely on data collected by a whole suite of observing systems—from satellites to surface stations to ocean buoys—operated by various government agencies and countries as well as climate records from ice cores, tree rings, corals, and sediments that help reconstruct past change.
Collecting and archiving data to meet the unique needs of climate change scienceMost of the instrumentation and observing systems used to monitor climate today were established to provide data for other purposes, such as predicting daily weather; advising farmers; warning of hurricanes, tornadoes and floods; managing water resources; aiding ocean and air transportation; and understanding the ocean. However, collecting climate data is unique because higher precision is often needed in order to detect climate trends, the observing programs need to be sustained indefinitely and accommodate changes in observing technology, and observations are needed at both global scales and at local scales to serve a range of climate information users.
Every report on climate change produced by the National Academies in recent years has recommended improvements to climate observing capabilities. A central theme of the report Adequacy of Climate Observing Systems (1999) is the need to dramatically upgrade our climate observing capabilities. The report presents ten climate monitoring principles that continue to be the basis for designing climate observing systems, including management of network change, careful calibration, continuity of data collection, and documentation to ensure that meaningful trends can be derived.
Another key concept for climate change science is the ability to generate, analyze, and archive long-term climate data records (CDRs) for assessing the state of the environment in perpetuity. In Climate Data Records from Environmental Satellites (2004), a climate data record is defined as a time series of measurements of sufficient length, consistency, and continuity to determine climate variability and change. The report identifies several elements of successful climate data record generation programs, ranging from effective, expert leadership to long-term commitment to sustaining the observations and archives.
Integrating knowledge and data on climate change through modelsAn important concept that emerged from early climate science in the 1980s was that Earth’s climate is not just a collection of long-term weather statistics, but rather the complex interactions or “couplings” of the atmosphere, the ocean, the land, and plant and animal life. Climate models are built using our best scientific knowledge, first modeling each process component separately and then linking them together to simulate these couplings.
Climate models are important tools for understanding how the climate operates today, how it may have functioned differently in the past, and how it may evolve in the future in response to forcings from both natural processes and human activities. Climate scientists can deal with uncertainty about future climate by running models with different assumptions of future population growth, economic development, energy use, and policy choices, such as those that affect air quality or influence how nations share technology. Models then offer a range of outcomes based on these different assumptions.
Modeling capability and accuracySince the first climate models were pioneered in the 1970s, the accuracy of models has improved as the number and quality of observations and data have increased, as computational abilities have multiplied, and as our theoretical understanding of the climate system has improved. Whereas early attempts at modeling used relatively crude representations of the climate, today’s models have very sophisticated and carefully tested treatment of hundreds of climate processes.
The National Academies’ report Improving Effectiveness of U.S. Climate Modeling (2001) offers several recommendations for strengthening climate modeling capabilities, some of which have already been adopted in the United States. At the time the report was published, U.S. modeling capabilities were lagging behind some other countries. The report identified a shortfall in computing facilities and highly skilled technical workers devoted to climate modeling. Federal agencies have begun to centralize their support for climate modeling efforts at the National Center for Atmospheric Research and the Geophysical Fluid Dynamics Laboratory. However, the U.S. could still improve the amount of resources it puts toward climate modeling as recommended in Planning Climate and Global Change Research (2003).
Climate change impacts will be unevenThere will be winners and losers from the impacts of climate change, even within a single region, but globally the losses are expected to outweigh the benefits. The regions that will be most severely affected are often the regions that are the least able to adapt. For example, Bangladesh, one of the poorest nations in the world, is projected to lose 17.5% of its land if sea level rises about 40 inches (1 m), displacing tens of thousands of people. Several islands throughout the South Pacific and Indian Oceans will be at similar risk of increased flooding and vulnerability to storm surges. Coastal flooding likely will threaten animals, plants, and fresh water supplies. Tourism and local agriculture could be severely challenged.
Wetland and coastal areas of many developed nations including United States are also threatened. For example, parts of New Orleans are as much as eight feet below sea level today. However, wealthy countries are much more able to adapt to sea level rise and threats to agriculture. Solutions could include building, limiting or changing construction codes in coastal zones, and developing new agricultural technologies.
The Arctic has warmed at a faster rate than the Northern Hemisphere over the past century. A Vision for the International Polar Year 2007-2008 (2004) reports that this warming is associated with a number of impacts including: melting of sea ice, which has important impacts on biological systems such as polar bears, ice-dependent seals, and local people for whom these animals are a source of food; increased snow and rainfall, leading to changes in river discharge and tundra vegetation; and degradation of the permafrost.
Preparing for climate changeOne way to begin preparing for climate change is to make the wealth of climate data and information already collected more accessible to a range of users who could apply it to inform their decisions. Such efforts, often called "climate services," are analogous to the efforts of the National Weather Service to provide useful weather information. Climate is becoming increasingly important to public and private decision making in various fields such as emergency management planning, water quality, insurance premiums, irrigation and power production decisions, and construction schedules. A Climate Services Vision (2001) outlines principles for improving climate services that include making climate data as user-friendly as weather services are today, and active and well-defined connections among the government agencies, businesses, and universities involved in climate change data collection and research.
Another avenue would be to develop practical strategies that could be used to reduce economic and ecological systems’ vulnerabilities to change. Such “no-regrets” strategies, recommended in Abrupt Climate Change: Inevitable Surprises (2002), provide benefits whether a significant climate change ultimately occurs or not, potentially reducing vulnerability at little or no net cost. No-regrets measures could include low-cost steps to: improve climate forecasting; slow biodiversity loss; improve water, land, and air quality; and make institutions—such as the health care enterprise, financial markets, and transportation systems—more resilient to major disruptions.
Reducing the causes of climate change
The climate change statement issued in June 2005 by 11 science academies, including the National Academy of Sciences, stated that despite remaining unanswered questions, the scientific understanding of climate change is now sufficiently clear to justify nations taking cost-effective steps that will contribute to substantial and long-term reduction in net global greenhouse gas emissions. Because carbon dioxide and some other greenhouse gases can remain in the atmosphere for many decades and major parts of the climate system respond slowly to changes in greenhouse gas concentrations, climate change impacts will likely continue throughout the 21st century and beyond. Failure to implement significant reductions in net greenhouse gas emissions now will make the job much harder in the future—both in terms of stabilizing their atmospheric abundances and in terms of experiencing more significant impacts.
At the present time there is no single solution that can eliminate future warming. As early as 1992, Policy Implications of Greenhouse Warming found that there are many potentially cost-effective technological options that could contribute to stabilizing greenhouse gas concentrations.
Meeting energy needs is a major challenge to slowing climate changeEnergy—either in the form of fuels used directly (i.e., gasoline) or as electricity produced using various fuels (fossil fuels as well as nuclear, solar, wind, and others)—is essential for all sectors of the economy, including industry, commerce, homes, and transportation. Energy use worldwide continues to grow with economic and population growth. Developing countries, China and India in particular, are rapidly increasing their use of energy, primarily from fossil fuels, and consequently their emissions of CO2. Carbon emissions from energy can be reduced by using it more efficiently or by switching to alternative fuels. It also may be possible to capture carbon emissions from electric generating plants and then sequester them.
Energy efficiency in all sectors of the U.S. economy could be improved. The 2002 National Academies’ report, Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards, evaluates car and light truck fuel use and analyzes how fuel economy could be improved. Steps range from improved engine lubrication to hybrid vehicles. The 2001 Academies report, Energy Research at DOE, Was It Worth It? addresses the benefits of increasing the energy efficiency of lighting, refrigerators and other appliances. Many of these improvements (e.g., high-efficiency refrigerators) are cost-effective means to significantly reducing energy use, but are being held back by market constraints such as consumer awareness, higher initial costs, or by the lack of effective policy.
Electricity can be produced without significant carbon emissions using nuclear power and renewable energy technologies (e.g., solar, wind, and biomass). In the United States, these technologies are too expensive or have environmental or other concerns that limit broad application, but that could change with technology development or if the costs of fossil fuels increase. Replacing coal-fired electric power plants with more efficient, modern natural-gas-fired turbines would reduce carbon emissions per unit of electricity produced.
Several technologies are being explored that would collect CO2 that would otherwise be emitted to the atmosphere from fossil-fuel-fired power plants, and then sequester it in the ground or the ocean. Successful, cost-effective sequestration technologies would weaken the link between fossil fuels and greenhouse gas emissions. The 2003 National Academies’ report, Novel Approaches to Carbon Management: Separation, Capture, Sequestration, and Conversion to Useful Products, discusses the development of this technology.
Capturing CO2 emissions from the tailpipes of vehicles is essentially impossible, which is one factor that has led to considerable interest in hydrogen as a fuel. As with electricity, hydrogen must be manufactured from primary energy sources. Significantly reducing carbon emissions when producing hydrogen from fossil fuels (currently the least expensive method) would require carbon capture and sequestration. Substantial technological and economic barriers in all phases of the hydrogen fuel cycle must first be addressed through research and development. The 2004 National Academies’ report, The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs, presents a strategy that could lead eventually to production of hydrogen from a variety of domestic sources—such as coal (with carbon sequestration), nuclear power, wind, or photo-biological processes—and efficient use in fuel cell vehicles.
Continued scientific efforts to address a changing climateThe task of mitigating and preparing for the impacts of climate change will require worldwide collaborative inputs from a wide range of experts, including natural scientists, engineers, social scientists, medical scientists, those in government at all levels, business leaders, and economists. Although the scientific understanding of climate change has advanced significantly in the last several decades, there are still many unanswered questions. Society faces increasing pressure to decide how best to respond to climate change and associated global changes, and applied research in direct support of decision making is needed.
National Academies’ Reports Cited in the Testimony
Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005)
Climate Data Records from Environmental Satellites (2004)
Implementing Climate and Global Change Research (2004)
A Vision for the International Polar Year 2007-2008 (2004)
The Hydrogen Economy: Opportunities, Costs, Barriers and R&D Needs (2004)
Understanding Climate Change Feedbacks (2003)
Planning Climate and Global Change Research (2003)
Novel Approaches to Carbon Management: Separation, Capture, Sequestration, and Conversion to Useful Products (2003)
Abrupt Climate Change: Inevitable Surprises (2002)
Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards (2002)
Climate Change Science: An Analysis of Some Key Questions (2001)
Improving the Effectiveness of U.S. Climate Modeling (2001)
A Climate Services Vision: First Steps Towards the Future (2001)
Energy Research at DOE, Was It Worth It? (2001)
Reconciling Observations of Global Temperature Change (2000)
Adequacy of Climate Observing Systems (1999)
Policy Implications of Greenhouse Warming (1992) -
Dr. Mario Molina
Witness Panel 1
Dr. Mario Molina
Hearing of the Committee on Energy and Natural Resources
Testimony by Professor Mario Molina
University of California, San Diego
July 21, 2005
Good Morning. I am very pleased to be here to discuss the science of climate change and to reflect on the very real challenge of making sound policy choices in the face of uncertainty. Climate change is perhaps the most worrisome global environmental problem confronting human society today. It involves a complex interplay of scientific, economic, and political issues. The impacts of climate change are potentially very large and will occur over a time scale of decades to centuries. The actions needed to respond to this challenge require substantial long-term commitments to change traditional economic development paths throughout the world. The ultimate solution to the challenge will require a fundamental transformation in the production and consumption of energy here in the United States and by developed and developing nations alike.I want to address the bulk of my remarks to the threshold question: Do we know enough about climate change to act now and to start doing something serious to address this problem? Let me first comment on what I think the role of scientists should be in answering this question. Ultimately policy decisions about climate change have to be made by society at large, and more specifically by policymakers. Scientists do not have any special privilege to make such decisions, but science does play a fundamental role on this issue. The climate system is very complicated and science does not have all the answers: there are uncertainties in predicting when and to what extent will the climate change as a consequence of a given course of human activities. However, scientists can estimate the probability that the earth’s climate will respond in certain ways. For simplicity the climate response is often represented as the increase in average global surface temperature of the planet say, by the end of the century. This information can be used by policymakers to assess the risks imposed by climate change and to device adequate responses to address the challenge.
Let me begin by simply summarizing what we know about climate change. I firmly embrace the view expressed in the recent Sense of the Senate Resolution that “there is a growing scientific consensus that human activity is a substantial cause of greenhouse gas accumulation in the atmosphere, “ and that these accumulating gasses are causing average temperatures to rise at a rate outside of natural variability.”
Simply stated, the world is warming.
• It is due to our emissions.
• More warming is inevitable -- but the amount of future warming is in our hands.
• Because CO2 accumulates and remains in the atmosphere, each generation inherits the emissions of all those who have gone before. Many future generations of human beings will wrestle with this issue.
• Modest amounts of warming will have both positive and negative impacts. But above a certain threshold, the impacts turn strongly negative for most nations, people, and biological systems.While there is a growing scientific consensus around the science of climate change, there is of course much that we do not fully understand about the timing, geographic distribution, and severity of the changes in climate - and the economic, environmental, and social impacts of these changes - that will result if heat -forcing emissions continue to increase. However, not knowing with certainty how the climate system will respond should not be an excuse for inaction. Policymakers are frequently, indeed usually, in the position of making decisions in the face of uncertainties. Usually, the presence of uncertainty means that we build in extra insurance to protect against the risk that consequences may be worse than we expect. It would be better, of course, if we knew exactly where the perfect balance between cost, risk, and benefit lies. But the fact is that we never have that luxury. Nevertheless, policy makers and individuals both must manage public and personal risks all the time and we do. Most people buy car insurance even though they don't know with any degree of certainty what their individual risk of being in a car accident might be, just as most doctors would advise an individual with a history of heart trouble to choose low-fat foods and exercise despite the many complex and usually unknowable factors that go into determining any individual person's risk of having a heart attack.
If we apply the same logic in setting goals for limiting the risks associated with future climate change, it becomes very clear that our current course now places us far outside the kinds of risk thresholds we typically apply in other areas of public policy. Put another way, there is now an overwhelming consensus that failure to limit greenhouse gas emissions will produce a risk of significant adverse consequences that is far higher than we find acceptable in other arenas. When facing a substantial chance of potentially catastrophic consequences and the near certainty of lesser negative effects, the only prudent course of action is to mitigate these risks. And let us be clear -- when we speak of potentially catastrophic consequences in this context we are talking about devastating impacts on ecosystems and biodiversity; severe flood damage to urban centers and island nations as sea level rises; significantly more destructive and frequent extreme weather events such as droughts and floods; seriously affected agricultural productivity in many countries; the exacerbation of certain diseases; population dislocations; etc.
A reasonable target, in my view, is to attempt to limit the global temperature increase to less than about 4 degrees Fahrenheit. Recent estimates indicate that stabilizing the amount of greenhouse gases in the atmosphere at the equivalent of twice the pre-industrial value of 280 ppm carbon dioxide provides only a 10-20 per cent chance of limiting global average temperature rise to 4 degrees Fahrenheit. Put another way, this means that the odds that average global temperatures will rise above 4 degrees is 80 to 90 percent. Unless society starts taking some aggressive actions now, we are well on our way to reaching perhaps even a tripling of pre-industrial carbon dioxide levels with far greater adverse economic and environmental consequences.
The risks to human society and ecosystems grow significantly if the average global surface temperature increases 5 degrees Fahrenheit or more. Such a large temperature increase might entail, for example, substantial agricultural losses, widespread adverse health impacts and greatly increased risks of water shortages. Furthermore, a very high proportion of the world’s coral reefs would be imperiled and many terrestrial ecosystems could suffer irreversible damage. The risk of runaway or abrupt climate change also increases rapidly if the average temperature increases above about 5 degrees Fahrenheit. It is possible, for example, that the West Antarctic and Greenland ice sheets will melt, raising sea levels more than ten meters over the period of a few centuries. It is also possible that the ocean circulation will change abruptly, perhaps shutting down the Gulf Stream.
I applaud the Committee for its commitment to explore legislative proposals consistent with the Sense of the Senate Resolution and moreover commend you for beginning this exploration with a discussion of climate science. As you may know, I am one of sixteen members of the National Commission for Energy Policy (NCEP). You will hear more about the Commission from Jason Grumet, our Executive Director, shortly. One of my main contributions to the Commission’s deliberations was helping the group understand the challenge of forging sound climate policy in the face of evolving scientific knowledge. Early on in our deliberations we agreed upon the following brief statement to guide our policy exploration. I offer it here for the Committee’s deliberations:
“(1) We understand that a scientific consensus has emerged that (a) global temperatures have been increasing at a rate that is outside the range of natural variability, (b) human emissions of CO2 and other greenhouse gases have been responsible for a part of this increase, and (c) continuation of these emission trends along “business as usual” lines could produce changes in climatic patterns in this century that will produce significant adverse impacts on human societies.
(2) There are many uncertainties in the details of the timing, geographic distribution, and severity of the changes in climate – and the economic, environmental, and social impacts of these changes – that will result if “business as usual” prevails. There are, likewise, significant uncertainties about the availability and costs of energy-supply and energy-end-use technologies that might be brought to bear to achieve much lower greenhouse-gas emissions than those expected on the “business as usual” trajectory.
(3) These uncertainties are cause for further research and development to try to reduce them, but they are not proper cause for taking no other action to reduce the risks from human-caused climate change. What is already known about these risks is sufficient reason to accelerate, starting now, the search for a mix of affordable technical and policy measures that will be able (a) to reduce greenhouse-gas emissions substantially from the “business as usual” trajectory in the aggregate over a relevant time frame, and (b) to adapt to the degree of climate change that cannot be avoided without incurring unreasonable costs. This is not the only major challenge in fashioning a sensible energy policy for the United States, but it is a challenge that no sensible energy policy can ignore.”
I thank you for your attention and look forward to working with the Committee in the weeks and months ahead.
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Dr. Jim Hurrell
Witness Panel 1
Dr. Jim Hurrell
Statement of
James W. Hurrell, Ph. D.*
Director, Climate and Global Dynamics Division
National Center for Atmospheric Research**Before the
U.S. Senate Committee on Energy and Natural Resources
21 July 2005
Hearing on Climate Change Science and Economics
Introduction
I thank Chairman Domenici, Ranking Member Bingaman, and the other Members of the Committee for the opportunity to speak with you today on the science of global climate change. My name is James W. Hurrell, Director of the Climate and Global Dynamics Division (CGD) at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. My personal research has centered on empirical and modeling studies and diagnostic analyses to better understand climate, climate variability and climate change. I have authored or co-authored more than 60 peer-reviewed scientific journal articles and book chapters, as well as dozens of other planning documents and workshop papers. I have given more than 65 invited talks worldwide, as well as many contributed presentations at national and international conferences on climate. I have also convened over one dozen national and international workshops, and I have served on several national and international science-planning efforts. Currently, I am extensively involved in the World Climate Research Programme (WCRP) on Climate Variability and Predictability (CLIVAR), and I serve as co-chair of Scientific Steering Committee of U.S. CLIVAR. I have also been involved in the assessment activities of the Intergovernmental Panel on Climate Change (IPCC) as a contributing author to chapters in both the third and fourth (in progress) assessment reports, and I have served on several National Research Council (NRC) panels. I am also a lead author on the U.S. Climate Change Science Program’s (CCSP) Synthesis and Assessment Product on Temperature Trends in the Lower Atmosphere.Throughout this testimony I will refer to both the IPCC and the CCSP. Briefly, the IPCC is a body of scientists from around the world convened by the United Nations jointly under the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO). Its mandate is to provide policy makers with an objective assessment of the scientific and technical information available about climate change, its environmental and socio-economic impacts, and possible response options. The IPCC reports on the science of global climate change and the effects of human activities on climate in particular. The fourth major assessment is underway (the previous assessments were published in 1990, 1995 and 2001) and is due to be published in 2007. Each new IPCC report reviews all the published literature over the previous 5 years or so, and assesses the state of knowledge, while trying to reconcile disparate claims, resolve discrepancies and document uncertainties. For the 2001 Third Assessment Report (TAR), Working Group I (which deals with how the climate has changed and the possible causes) consisted of 123 lead authors, 516 contributors, 21 review editors, and over 700 reviewers. It is a very open process. The TAR concluded that climate is changing in ways that cannot be accounted for by natural variability and that “global warming” is happening.
The U.S. CCSP was established in 2002 to coordinate climate and global change research conducted in the United States. Building on and incorporating the U.S. Global Change Research Program of the previous decade, the program integrates federal research on climate and global change, as sponsored by 13 federal agencies and overseen by the Office of Science and Technology Policy, the Council on Environmental Quality, the National Economic Council and the Office of Management and Budget. A primary objective of the CCSP is to provide the best possible scientific information to support public discussion and government and private sector decision-making on key climate-related issues. To help meet this objective, the CCSP is producing a series of synthesis and assessment products that address its highest priority research, observation, and decision-support needs. Each of these products will be written by a team of authors selected on the basis of their past record of interest and accomplishment in the given topic. The Product on Temperature Trends in the Lower Atmosphere focuses on both understanding reported differences between independently produced data sets of temperature trends for the surface through the lower stratosphere and comparing these data sets to model simulations.
Observed Climate Change
a. Surface TemperatureImprovements have been made to both land surface air temperature and sea surface temperature (SST) data during the five years since the TAR was published. The improvements relate to improved coverage, particularly over the Southern Hemisphere (SH) in the late 19th Century, and daily temperature data for an increasing number of land stations have also become available, allowing more detailed assessment of extremes, as well as potential urban influences on both large-scale temperature averages and microclimate.
The globe is warming. Claims to the contrary are not credible. Three different analyses of observations of surface temperature averaged across the globe show a linear warming trend of 0.6ºC ±0.2ºC since the beginning of the 20th Century. Rates of temperature rise are greater in recent decades: since 1979, global surface temperatures have increased more than 0.4ºC. Land regions have warmed the most (0.7ºC since 1979), with the greatest warming in the boreal winter and spring months over the Northern Hemisphere (NH) continents. A number of recent studies indicate that effects of urbanization and land-use change on the land-based temperature record are negligible as far as continental- and hemispheric-space averages are concerned, because the very real but local effects are accounted for. Recent warming is strongly evident at all latitudes over each of the ocean basins and, averaged over the globe, the SSTs have warmed 0.35ºC since 1979. The trends over the past 25 years have been fairly linear; however the global temperature changes over the entire instrumental record are best described by relatively steady temperatures from 1861-1920, a warming of about 0.3ºC to 1950, a cooling of about 0.1ºC until the mid-1970s, and a warming of about 0.55ºC since then. Thus, global surface temperatures today are about 0.75ºC warmer than at the beginning of the 20th Century.
The warmest year in the 145-year global instrumental record remains 1998, since the major 1997-98 El Niño enhanced it. The years 2002–2004 are the 2nd, 3rd and 4th warmest years in the series since 1861 and nine of the last 10 years (1995 to 2004) – the exception being 1996 – are among the ten warmest years in the instrumental record. Based on reconstructions of temperature from proxy data, like tree rings and ice cores, several studies have also concluded that NH surface temperatures are warmer now than at any time in at least the last 1,000 years.
b. Consistency with other observed changes
The warming described above is consistent with a body of other observations that gives a consistent picture of a warming world. For example, there has been a widespread reduction in the number of frost days in middle latitude regions, principally due to an earlier last day of frost in spring rather than a later start to the frost season in autumn. There has been an increase in the number of warm extremes and a reduction in the number of daily cold extremes, especially at night. The amount of water vapor in the atmosphere has increased over the global oceans by 1.2 ± 0.3% from 1988 to 2004, consistent in patterns and amount with changes in SST and a fairly constant relative humidity. Widespread increases in surface water vapor are also found. Ocean temperatures have warmed at depth as well, and global sea levels have risen 15-20 centimeters over the 20th Century: as the oceans warm, seawater expands and sea level rises.
There has been a nearly worldwide reduction in mountain glacier mass and extent. Snow cover has decreased in many NH regions, particularly in the spring season and this is consistent with greater increases in spring than autumn surface temperatures in middle latitude regions. Sea-ice extents have decreased in the Arctic, particularly in the spring and summer seasons, and patterns of the changes are consistent with regions showing a temperature increase. The Arctic (north of 65ºN) average annual temperature has increased since the 1960s and is now warmer (at the decade timescale) than conditions experienced during the 1920–1945 period (where much of the earlier global warming was centered). In the Antarctic, there are regional patterns of warming and cooling related to changes in the atmospheric circulation. The warming of the Peninsula region since the early 1950s is one the largest and the most consistent warming signals observed anywhere in the world. Large reductions in sea-ice have occurred to the west in the Bellingshausen Sea, and on the eastern side of Peninsula, large reductions in the size of Larsen Ice shelf have occurred.
c. Temperature of the Upper Air
Radiosonde releases provide the longest record of upper-air measurements, and these data show similar warming rates to the surface temperature record since 1958. Unfortunately, however, vast regions of the oceans and portions of the landmasses (especially in the Tropics) are not monitored so that there is always a component of the global or hemispheric mean temperature that is missing. Moreover, like all measurement systems, radiosonde records of temperature have inherent uncertainties associated with the instruments employed and with changes in instrumentation and observing practices, among other factors. Fundamentally, these uncertainties arise because the primary purpose of radiosondes is to help forecast the weather, not monitor climate variability and change. Therefore, all climate data sets require careful examination for instrument biases and reliability (quality control) and to remove changes that might have arisen for non-climatic reasons (a process called “homogenization”.) It is difficult to remove all non-climatic effects, and ideally multiple data sets should be produced independently to see how sensitive results are to homogenization choices. This has been the case for the surface record, but unfortunately much less so for the radiosonde record (although efforts are increasing.)
For this reason, much attention has been paid to satellite estimates of upper-air temperatures, in particular because they provide true global coverage. Of special interest have been estimates of tropospheric and stratospheric temperatures over thick atmospheric layers obtained from microwave sounding units (MSU) onboard NOAA polar-orbiting satellites since 1979. Initial analyses of the MSU data by scientists at the University of Alabama, Huntsville (UAH) indicated that temperatures in the troposphere showed little or no warming, in stark contrast with surface air measurements. Climate change skeptics have used this result to raise questions about both the reliability of the surface record and the cause of the surface warming, since human influences thought to be important are expected to increase temperatures both at the surface and in the troposphere. They also have used the satellite record to caste doubt on the utility of climate models, which simulate both surface and tropospheric warming in over recent decades.
In an attempt to resolve these issues, the NRC in 2000 studied the problem and concluded that “the warming trend in global-mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming during the 20th Century. The disparity between surface and upper air trends in no way invalidates the conclusion that surface temperature has been rising.” The NRC further found that corrections in the MSU processing algorithms brought the satellite data record into slightly closer alignment with surface temperature trends, but substantial discrepancies remained. As further noted by the TAR, some, but not all, of these remaining discrepancies could be attributed to the fact that the surface and the troposphere respond differently to climate forcings, so that trends over a decade or two should not necessarily be expected to agree.
Since the IPCC and NRC assessments, new data sets and modeling simulations have become available which are helping to resolve this apparent dilemma. The CCSP Assessment Product on Temperature Trends in the Lower Atmosphere is assessing these new data, and the preliminary report (which has been reviewed by the NRC) finds that the surface and upper-air records of temperature change can now, in fact, be reconciled. Moreover, the overall pattern of observed temperature change in the vertical is consistent with that simulated by today’s climate models.
Several developments since the TAR are especially notable:
• A second, independent record of MSU temperatures has become available from scientists at the Remote Sensing Systems (RSS) Laboratory. Although both the UAH and RSS groups start from the same raw radiance data, they apply different construction methods of merging the MSU data from one satellite to the next. The result is that, while both data sets indicate the middle troposphere has warmed since 1979, the RSS estimate is ~0.1ºC decade-1 warmer than the UAH estimate. Moreover, the RSS trend is not statistically different from the observed surface warming since 1979. The difference in tropospheric temperature trends between these two products highlights the issue of temporal homogeneity in the satellite data.
• Both UAH and RSS MSU products support the conclusion that the stratosphere has undergone strong cooling since 1979, due to observed stratospheric ozone depletion.
• Because about 15% of the MSU signal for middle tropospheric temperature actually comes from the lower stratosphere, the real warming of the middle troposphere is greater than that indicated by the MSU data sets. This has been confirmed by new analyses that explicitly remove the stratospheric influence, which is about –0.08ºC decade-1 on middle tropospheric MSU temperature trends since 1979.
• By differencing MSU measurements made at different slant angles, both the UAH and the RSS groups have produced updated data records weighted more toward the lower troposphere. The RSS product exhibits a warming trend that is 0.2ºC decade-1 larger than that from UAH. In part, this discrepancy is because adjustments for diurnal cycle corrections required from satellite drift had the wrong sign in the UAH record. As a result, a new UAH record is being prepared, and the current version is regarded as obsolete.The various new data sets of upper-air temperature are very important because their differences highlight differences in construction methodologies. It therefore becomes possible to estimate the uncertainty in satellite-derived temperature trends that arises from different methods.
d. Extremes
For any change in mean climate, there is likely to be an amplified change in extremes. The wide range of natural variability associated with day-to-day weather means that we are unlikely to notice most small climate changes except for changes in the occurrence of extremes. Extreme events, such as heat waves, floods and droughts, are exceedingly important to both natural systems and human systems and infrastructure. We are adapted to a range of natural weather variations, but it is the extremes of weather and climate that exceed tolerances.
In several regions of the world indications of a change in various types of extreme weather and climate events have been found. So far, the most prominent indication of a change in extremes is the evidence of increases in moderate to heavy precipitation events over the middle latitudes in the last 50 years, even for regions where annual precipitation totals are decreasing. Further indications of a robust change include the observed trend to fewer frost days associated with the average warming in most middle latitude regions. Results for temperature-related daily extremes are also relatively coherent for some measures. Many regions show increased numbers of warm days/nights (and lengthening of heat waves) and even more reductions in the number of cold days/nights, but changes are not ubiquitous.Trends in tropical storm frequency and intensity are masked by large natural variability on multiple timescales. Increases may be occurring in recent years, but apart from the North Atlantic basin, most measures only begin in the 1950s or 1960s and have likely missed some events in the early decades. Numbers of hurricanes in the North Atlantic have been above normal in 8 of the last 10 years, but levels were about as high in the 1950s and 1960s. This pattern continues this summer, with a very active hurricane season already evident and SSTs at record high levels.
Modeling and Attribution of Climate Changea. Improved simulations of past climate
The best climate models encapsulate the current understanding of the physical processes involved in the climate system, the interactions, and the performance of the system as a whole. They have been extensively tested and evaluated using observations. They are exceedingly useful tools for carrying out numerical climate experiments, but they are not perfect, and some models are better than others. Uncertainties arise from shortcomings in our understanding of climate processes operating in the atmosphere, ocean, land and cryosphere, and how to best represent those processes in models. Yet, in spite of these uncertainties, today’s best climate models are now able to reproduce the climate of the past century, and simulations of the evolution of global surface temperature over the past millennium are consistent with paleoclimate reconstructions.
As a result, climate modelers are able to test the role of various forcings in producing the observed changes in global temperature temperatures. Forcings imposed on the climate system can be natural in origin, such as changes in solar luminosity or volcanic eruptions, the latter adding considerable amounts of aerosol to the upper atmosphere for up to two years. Human activities also increase aerosol concentrations in the atmosphere, mainly through the injection of sulfur dioxide from power stations and through biomass burning. A direct effect of sulfate aerosols is the reflection of a fraction of solar radiation back to space, which tends to cool the Earth’s surface. Other aerosols (like soot) directly absorb solar radiation leading to local heating of the atmosphere, and some absorb and emit infrared radiation. A further influence of aerosols is that many act as nuclei on which cloud droplets condense, affecting the number and size of droplets in a cloud and hence altering the reflection and the absorption of solar radiation by the cloud. The precise nature of aerosol/cloud interactions and how they interact with the water cycle remains a major uncertainty in our understanding of climate processes. Because man-made aerosols are mostly introduced near the Earth’s surface, they can be washed out of the atmosphere by rain. They therefore typically remain in the atmosphere for only a few days, and they tend to be concentrated near their sources such as industrial regions. Therefore, they affect climate with a very strong regional pattern and usually produce cooling.
In contrast, greenhouse gases such as carbon dioxide and methane are not washed out, so they have lifetimes of decades or longer. As a result, they build up in amounts over time, as has been observed. Greenhouse gas concentrations in the atmosphere are now higher than at any time in at least the last 750,000 years. It took at least 10,000 years from the end of the last ice age for levels of carbon dioxide to increase 100 parts per million by volume (ppmv) to 280 ppmv, but that same increase has occurred over only the past 150 years to current values of over 370 ppmv. About half of that increase has occurred over the last 35 years, owing mainly to combustion of fossil fuels and deforestation. In the absence of controls, future projections are that the rate of increase in carbon dioxide amount may accelerate, and concentrations could double from pre-industrial values within the next 50 to 100 years.
Climate model simulations that account for such changes in forcings have now reliably shown that global surface warming of recent decades is a response to the increased concentrations of greenhouse gases and sulfate aerosols in the atmosphere. When the models are run without these forcing changes, they fail to capture the almost linear increase in global surface temperatures since the mid-1970s. But when the anthropogenic forcings are included, the models simulate the observed temperature record with impressive fidelity. These same model experiments also reveal that changes in solar luminosity account for much of the warming in the first half of the 20th Century. Such results increase our confidence in the observational record and our understanding of how temperature has changed. They also mean that the time histories of the important forcings are reasonably known, and that the processes being simulated models are adequate enough to make the models very valuable tools.
b. Commitment to further climate change
The ability of climate models to simulate the past climate record gives us increased confidence in their ability to simulate the future. Moreover, the attribution of the recent climate change to increased concentrations of greenhouse gases in the atmosphere has direct implications for the future. Because of the long lifetime of carbon dioxide and the slow equilibration of the oceans, there is a substantial future commitment to further global climate change even in the absence of further emissions of greenhouse gases into the atmosphere. Several modeling groups have performed “commitment” runs in order to examine the climate response even if the concentrations of greenhouse gases in the atmosphere had been stabilized in the year 2000. The exact results depend upon the model, but they all show a further global warming of about another 0.5ºC, and additional and significant sea level rises caused by thermal expansion of the oceans by the end of the 21st Century. Further glacial melt is also likely.
The climate modeling groups contributing to the Fourth IPCC Assessment Report have produced the most extensive internationally coordinated climate change experiment ever performed (21 global coupled models from 14 countries). This has allowed better quantification of multi-model responses to three scenarios of 21st century climate corresponding to low (550 ppmv), medium (690 ppmv) and high (820 ppmv) increases of carbon dioxide concentrations by the year 2100. In spite of differences among models and the uncertainties that exist, the models produce some consistent results:
• Over the next decade or two, all models produce similar warming trends in global surface temperatures, regardless of the scenario.
• Nearly half of the early 21st Century climate change arises from warming we are already committed to. By mid-century, the choice of scenario becomes more important for the magnitude of warming, and by the end of the 21st Century there are clear consequences for which scenario is followed.
• The pattern of warming in the atmosphere, with a maximum in the upper tropical troposphere and cooling in the stratosphere, becomes established early in this century.
• Geographical patterns of warming show greatest temperature increases at high northern latitudes and over land, with less warming over the southern oceans and North Atlantic. In spite of a slowdown of the meridional overturning circulation and changes in the Gulf Stream in the ocean across models, there is still warming over the North Atlantic and Europe due to the overwhelming effects of the increased concentrations of greenhouse gases.
• Precipitation generally increases in the summer monsoons and over the tropical Pacific in particular, with general decreases in the subtropics and some middle latitude areas, and increases at high latitudes.
c. Increasing complexity of models
As our knowledge of the different components of the climate system and their interactions increases, so does the complexity of climate models. Historical changes in land use and changes in the distribution of continental water due to dams and irrigation, for instance, need to be considered. Future projected land cover changes due to human land uses are also likely to significantly affect climate, and these effects are only now being included in climate models.One of the major advances in climate modeling in recent years has been the introduction of coupled climate-carbon models. Climate change is expected to influence the capacities of the land and oceans to act as repositories for anthropogenic carbon dioxide, and hence provide a feedback to climate change. These models now allow us to assess the nature of this feedback. Results show that carbon sink strengths are inversely related to the rate of fossil fuel emissions, so that carbon storage capacities of the land and oceans decrease and climate warming accelerates with faster carbon dioxide emissions. Furthermore, there is a positive feedback between the carbon and climate systems, so that further warming acts to increase the airborne fraction of anthropogenic carbon dioxide and amplify the climate change itself.
Policy implications
In summary, the scientific understanding of climate change is now sufficiently clear to show that climate change from global warming is already upon us. Uncertainties remain, especially regarding how climate will change at regional and local scales. But the climate is changing and the uncertainties make the need for action all the more imperative. At the same time, it should be recognized that mitigation actions taken now mainly have benefits 50 years and beyond now. This also means that we will have to adapt to climate change by planning for it and making better predictions of likely outcomes on several time horizons. My personal view it that it is vital that all nations identify cost-effective steps that they can take now, to contribute to substantial and long-term reductions in net global greenhouse gas emissions. Action taken now to reduce significantly the build-up of greenhouse gases in the atmosphere will lessen the magnitude and rate of climate change. While some changes arising from global warming are benign or even beneficial, the rate of change as projected exceeds anything seen in nature in the past 10,000 years. It is apt to be disruptive in many ways. Hence it is also vital to plan to cope with the changes, such as enhanced droughts, heat waves and wild fires, and stronger downpours and risk of flooding. Managing water resources will be major challenge in the future.
Again, I appreciate the opportunity to address the Committee concerning the science of global climate change – a topic that is of the utmost importance for the future of our planet.
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Sir John Houghton
Witness Panel 1
Sir John Houghton
Testimony to the US Senate - Energy and Natural Resources Committee
Sir John Houghton, 21 July 2005I consider it a privilege to be asked to testify to your committee this morning. Thank you for inviting me. On my last visit to the United States in March I was briefing the National Association of Evangelicals and was most pleased to find that large and influential body engaging with this issue of global climate change - the most serious environmental issue facing the world today.
The basic science of global warming
Let me start with a quick summary of the basic science of Global Warming. By absorbing infra-red or ‘heat’ radiation from the earth’s surface, ‘greenhouse gases’ present in the atmosphere, such as water vapour and carbon dioxide, act as blankets over the earth’s surface, keeping it warmer than it would otherwise be. The existence of this natural ‘greenhouse effect’ has been known for nearly two hundred years; it is essential to the provision of our current climate to which ecosystems and we humans have adapted.
Since the beginning of the industrial revolution around 1750, one of these greenhouse gases, carbon dioxide has increased by over 30% and is now at a higher concentration in the atmosphere than it has been for many hundreds of thousands of years (Fig 1). Chemical analysis demonstrates that this increase is due largely to the burning of fossil fuels - coal, oil and gas. If no action is taken to curb these emissions, the carbon dioxide concentration will rise during the 21st century to two or three times its preindustrial level.
Fig 1. Concentration of carbon dioxide in the atmosphere from 1000 AD and projected to 2100 under typical IPCC scenarios .
Fig 2. Variations of the average near surface air temperature: 1000-1861, N Hemisphere from proxy data; 1861-2000, global instrumental; 2000-2100, under a range of IPCC projections with further shading to indicate scientific uncertainty .
The climate record over the last 1000 years (Fig 2) shows a lot of natural variability – including, for instance, the ‘medieval warm period’ and the ‘little ice age’ . The rise in global average temperature (and its rate of rise) during the 20th century is well outside the range of known natural variability. The year 1998 is the warmest year in the instrumental record. A more striking statistic is that each of the first 8 months of 1998 was the warmest on record for that month. There is strong evidence that most of the warming over the last 50 years is due to the increase of greenhouse gases, especially carbon dioxide. Confirmation of this is also provided by observations of the warming of the oceans . The period of ‘global dimming’ from about 1950 to 1970 is most likely due to the increase in atmospheric particles (especially sulphates) from industrial sources. These particles reflect sunlight, hence tending to cool the surface and mask some of the warming effect of greenhouse gases. Global climate models that include human induced effects (greenhouse gas increases and particles) and known natural forcings (e.g. variations in solar radiation and the effects of volcanoes) can provide good simulations of the twentieth century profile of global average temperature change.
Over the 21st century the global average temperature is projected to rise by between 2 and 6 ºC (3.5 to 11 ºF) from its preindustrial level; the range represents different assumptions about emissions of greenhouse gases and the sensitivity of the climate model used in making the estimate (Fig 2). For global average temperature, a rise of this amount is large. The difference between the middle of an ice age and the warm periods in between is only about 5 or 6 ºC (9 to 11 ºF). So, associated with likely warming in the 21st century will be a rate of change of climate equivalent to say, half an ice age in less than 100 years – a larger rate of change than for at least 10,000 years. Adapting to this will be difficult for both humans and many ecosystems.
The impacts of human induced climate change
Talking in terms of changes of global average temperature, however, tells us rather little about the impacts of global warming on human communities. Some of the most obvious impacts will be due to the rise in sea level that occurs because ocean water expands as it is heated. The projected rise is of the order of half a metre (20 inches) a century and will continue for many centuries – to warm the deep oceans as well as the surface waters takes a long time. This will cause large problems for human communities living in low lying regions, for instance in the Everglades region of Florida. Many areas, for instance in Bangladesh (where about 10 million live within the one metre contour – Fig 3), southern China, islands in the Indian and Pacific oceans and similar places elsewhere in the world, will be impossible to protect and many millions will be displaced.
Fig 3. Land affected in Bangladesh by various amounts of sea level rise
There will also be impacts from extreme events. The extremely unusual high temperatures in central Europe during the summer of 2003 led to the deaths of over 20,000 people. Careful analysis shows that it is very likely that a large part of the cause of this event is due to increases in greenhouse gases and projects that such summers are likely to be the norm by the middle of the 21st century and cool by the year 2100.
Water is becoming an increasingly important resource. A warmer world will lead to more evaporation of water from the surface, more water vapour in the atmosphere and more precipitation on average. Of greater importance is the fact that the increased condensation of water vapour in cloud formation leads to increased latent heat of condensation being released. Since this latent heat release is the largest source of energy driving the atmosphere’s circulation, the hydrological cycle will become more intense. This means a tendency to more intense rainfall events and also less rainfall in some semi-arid areas. Since, on average, floods and droughts are the most damaging of the world’s disasters (see box), their greater frequency and intensity is bad news for most human communities and especially for those regions such as south east Asia and sub-Saharan Africa where such events already occur only too frequently.
BOX
Major floods in the 1990s
• 1991, 1994-5, 1998 – China; average disaster cost 1989-96, 4% of GDP
• Mississipi & Missouri, USA; flooded area equal to one of great lakes
• 1997 – Europe; 162,000 evacuated and > 5bn $ loss
• 1998 - Hurricane Mitch in central America; 9000 deaths,
economic loss in Honduras &Nicaragua 70% & 45% of GDP
• 1999 – Venezuela; flooding led to landslide, 30,000 deaths
• 2000-1 - Mozambique; two floods leave more than half a million homeless
END OF BOXRegarding extreme events and disasters, it is often pointed out that climate possesses large natural variability and such events have been common occurrences over the centuries. It is not possible, for instance, when a disaster occurs to attribute that particular event to increasing greenhouse gases (except perhaps for the 2003 heat wave mentioned above). So, what is the evidence that they will increase in a globally warmed world? First, there is our understanding of the basic science of climate change that I have briefly outlined. Secondly, increasing evidence is provided from observations. Significant increases have been observed in the number of intense rainfall events especially over areas like the USA where there is good data coverage. Data from insurance companies show an increase in economic losses in weather related disasters of a factor of 10 in real terms between the 1950s and the 1990s. Some of this can be attributed to an increase in vulnerability to such disasters. However, a significant part of the trend has also arisen from increased storminess especially in the 1980s and 1990s.
Thirdly, increased risk of heat waves, floods and droughts are some of the most robust projections of climate models that take into account in a comprehensive way all the physical and dynamical processes involved in climate change. For instance, a study for the area of central Europe, with doubled atmospheric carbon dioxide concentration (likely to occur during the second half of the twenty first century), indicates an decrease in the return period of flooding events by about a factor of five (e.g. from 50 years to 10 years) .
Tropical cyclones are particular damaging storms that occur in the sub tropics. They require special mention because no evidence exists for an increase in their number as the earth warms although an increase is considered likely in peak wind and precipitation intensities in such systems.
Sea level rise, changes in water availability and extreme events will cause the most damaging impacts of human induced climate change . They will lead to increasing pressure from many millions of environmental refugees.
In addition to the main impacts summarised above are changes about which there is less certainty, but if they occurred would be highly damaging and possibly irreversible. For instance, large changes are being observed in polar regions. If the temperature rises more than about 3 ºC (~5 ºF) in the area of Greenland, it is estimated that melt down of the ice cap would begin. Complete melt down is likely to take 1000 years or more but it would add 7 metres (23 feet) to the sea level.
A further concern is regarding the Thermo-Haline Circulation (THC) – a circulation in the deep oceans, partially sourced from water that has moved in the Gulf Stream from the tropics to the region between Greenland and Scandanavia. Because of evaporation on the way, the water is not only cold but salty, hence of higher density than the surrounding water. It therefore tends to sink and provides the source for a slow circulation at low levels that connects all the oceans together. This sinking assists in maintaining the Gulf Stream itself. In a globally warmed world, increased precipitation together with fresh water from melting ice will decrease the water’s salinity making it less likely to sink. The circulation will therefore weaken and possibly even cut off, leading to large regional changes of climate. All climate models indicate the occurrence of this weakening. Evidence from paleoclimate history shows that such cut-off has occurred at times in the past. It is such an event that is behind the highly speculative happenings in the film, The day after tomorrow.
I have spoken so far about adverse impacts. However, there are some positive impacts. For instance, in Siberia and other areas at high northern latitudes, winters will be less cold and growing seasons will be longer. Also, increased concentrations of carbon dioxide have a fertilising effect on some plants and crops which, providing there are adequate supplies of water and nutrients, will lead to increased crop yields in some places, probably most notably in northern mid latitudes. However, careful studies demonstrate that adverse impacts will far outweigh positive effects, the more so as temperatures rise more than 1 or 2 ºC (2 to 3.5 ºF) above preindustrial.
Many people ask how sure we are about the scientific story I have just presented. Let me explain that it is based very largely on the extremely thorough work of the Intergovernmental Panel on Climate Change (IPCC) and its last major report published in 2001. The scientific literature on climate change has increased enormously over the last decade. The basic science of anthropogenic climate change has been confirmed. The main uncertainties lie in our knowledge of feedbacks in the climate system especially those associated with the effects of clouds. Recent research has tended to indicate increased likelihood of the more damaging impacts.
The Intergovernmental Panel on Climate Change (IPCC)
Let me explain more about the work of the IPCC. It was formed in 1988 jointly by the World Meteorological Organisation and the United Nations Environment Programme. I had the privilege of being chairman or co-chairman of the Panel’s scientific assessment from 1988 to 2002. Hundreds of scientists drawn from many countries were involved as contributors and reviewers in these assessments. The IPCC has produced three assessments - in 1990, 1995 and 2001 – covering science, impacts and analyses of policy options. The IPCC 2001 report is in four volumes each of about 1000 pages and containing many thousands of references to the scientific literature . Each chapter of the Report went through two major reviews, first by hundreds of scientists in the scientific community (any scientist who wished could take part in this) and secondly, by governments. No assessment on any other scientific topic has been so thoroughly researched and reviewed.
Because the IPCC is an intergovernmental body, the reports’ Summaries for Policymakers were agreed sentence by sentence by meetings in which governmental delegates from about 100 countries (including all the world’s major countries) work with around 40 leading scientists representing the scientific community. It is sometimes supposed that the presence of governments implies political interference with the process. That has not been the case. In any event, governments taking part come from the complete spectrum of political agendas. These are scientific meetings in which all proposals for changes in the text must be based either on scientific arguments or on a desire for clearer presentation. In every case, the process has resulted in documents with overall improved scientific clarity and balance.
The work of the IPCC is backed by the worldwide scientific community. A joint statement of support was issued in May 2001 by the national science academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden and the UK. It stated ‘We recognize the IPCC as the world’s most reliable source of information on climate change and its causes, and we endorse its method of achieving consensus.’ In 2001, a report of the United States National Academy of Sciences commissioned by the President George W Bush administration, supported the IPCC’s conclusions . A joint statement issued in June 2005 by the science academies of all the G8 countries together with the academies of Brazil, China and India also endorsed the work and conclusions of the IPCC .
Let me comment further on the issues of uncertainty and balance as expressed in the work of the IPCC. There are very large amounts of data available to the scientist looking for evidence of climate change. Examples abound of those who approach the data with preconceived agendas and who have selected data to fit those agendas - for instance purporting to prove either that there is little or no evidence for human induced change or that the world is heading for a future that could mean the end of the human race. The task of the IPCC has been to review all the evidence in a balanced manner and honestly and objectively to distinguish what is reasonably well known and understood from those areas with large uncertainty. The reports have differentiated between degrees of uncertainty, where possible providing numerical estimates of uncertainty. A large part of the IPCC process, taking many days of scientists’ time, has been taken up with discussion and correspondence about how best to present uncertainty.
Let me mention a further point on the uncertainty issue. In the IPCC reports, because they are scientific documents, uncertainty tends to be mentioned frequently giving the impression to the casual reader that the uncertainty in the conclusions is larger than it is in many other areas of our experience with which comparison could be made. What is important to realise is that there is a high degree of certainty that significant human induced climate change is occurring and will continue to occur. A forecast of little or no such climate change is almost certainly wrong.
The Framework Convention on Climate Change
Because of the work of the IPCC and its first report in 1990, the Earth Summit at Rio de Janeiro in 1992 could address the climate change issue and the action that needed to be taken. The Framework Convention on Climate Change (FCCC) - agreed by over 160 countries, signed by President George Bush Snr for the USA and subsequently ratified unanimously by the US Senate – agreed that Parties to the Convention should take “precautionary measures to anticipate, prevent or minimise the causes of climate change and mitigate its adverse effects. Where there are threats of irreversible damage, lack of full scientific certainty should not be used as a reason for postponing such measures.”
More particularly the Objective of the FCCC in its Article 2 is “to stabilise greenhouse gas concentrations in the atmosphere at a level that does not cause dangerous interference with the climate system” and that is consistent with sustainable development. Such stabilisation would also eventually stop further climate change. However, because of the long time that carbon dioxide resides in the atmosphere, the lag in the response of the climate to changes in greenhouse gases (largely because of the time taken for the ocean to warm), and the time taken for appropriate human action to be agreed, the achievement of such stabilisation will take at least the best part of a century.
Stabilization of carbon dioxide
Global emissions of carbon dioxide to the atmosphere from fossil fuel burning are currently approaching 7 billion tonnes of carbon per annum and rising rapidly (Fig 4). Unless strong measures are taken they will reach two or three times their present levels during the 21st century and stabilisation of greenhouse gas concentrations or of climate will be nowhere in sight. To stabilise carbon dioxide concentrations in accordance with the FCCC Objective, emissions during the 21st century must reduce to a fraction of their present levels before the century’s end.
The reductions in emissions must be made globally; all nations must take part. However, there are very large differences between greenhouse gas emissions in different countries. Expressed in tonnes of carbon per capita per annum, they vary from about 5.5 for the USA, 2.2 for Europe, 0.7 for China and 0.2 for India (Fig 5). Ways need to be found to achieve reductions that are both realistic and equitable.
Fig 4. Global emissions of carbon dioxide from fossil fuel burning (in billions of tonnes of carbon) up to 1990 and as projected to 2100 under World Energy Council scenarios , A’s and B’s with various ‘business as usual assumptions’ and C for ‘ecologically driven scenario’ that would lead to stabilisation of carbon dioxide concentration at about 450 ppm.
Fig 5. Carbon dioxide emissions in 2000 per capita for different countries and groups of countries .
The Kyoto Protocol set up by the FCCC represents a beginning for the process of reduction, averaging about 5% below 1990 levels by 2012 by those developed countries who have ratified the protocol. It is an important start demonstrating the achievement of a useful measure of international agreement on such a complex issue. It also introduces for the first time international trading of greenhouse gas emissions so that reductions can be achieved in the most cost effective ways.
Serious discussion is now beginning about international agreements for emissions reductions post Kyoto. These must include all major emitters in both developed and developing countries. On what eventual level of stabilisation, of carbon dioxide for instance, should these negotiations focus? To stop damaging climate change the level needs to be as low as possible. In the light of the FCCC Objective it must also allow for sustainable development. Let me give two examples of stabilisation proposals. In 1996 the European Commission proposed a limit for the rise in global average temperature from its preindustrial value of 2 ºC – that implies a stabilisation level for carbon dioxide of about 430 ppm (allowing for the effect of other greenhouse gases at their 1990 levels). The second example comes from Lord John Browne, Chief Executive Officer of British Petroleum, one of the world’s largest oil companies, who in a recent speech proposed 'stabilisation in the range 500-550 ppm' that 'with care could be achieved without disrupting economic growth.'
Let us consider carbon dioxide stabilisation at 500 ppm. If the effect of other greenhouse gases at their 1990 levels is added, it is about equivalent to doubled carbon dioxide at its preindustrial level and a rise in global averaged temperature of about 2.5 ºC. Although climate change would eventually largely be halted – although not for well over a hundred years - the climate change impacts at such a level would be large. A steady rise in sea level will continue for many centuries, heat waves such as in Europe in 2003 would be commonplace, devastating floods and droughts would be much more common in many places and Greenland would most likely start to melt down. The aim should be therefore to stabilise at a lower level. But is that possible?
The International Energy Agency (IEA) in 2004 published a World Energy Outlook that in their words ‘paints a sobering picture of how the global energy system is likely to evolve from now to 2030’. With present governments’ policies, the world’s energy needs will be almost 60% higher in 2030 that they are now. Fossil fuels will dominate, meeting most of the increase in overall energy use. Energy-related emissions of carbon dioxide will grow marginally faster than energy use and will be more than 60% higher in 2030 than now (Fig 6, reference scenario). Over two-thirds of the projected increase in emissions will come from developing countries.
Fig 6. Carbon dioxide emissions from fossil fuel burning and profile leading to stabilisation at 500 ppm (a, b and c) and 450 ppm (d). Emissions data from International Energy Agency scenarios ; reference (a), alternative (b) for developed countries (red) and developing (blue). For (c) and (d) see text.The Outlook also presents an Alternative Scenario that analyses the global impact of environmental and energy-security policies that countries around the world are already considering as well as the effects of faster deployment of energy-efficient technologies. However, even in this scenario, global emissions in 2030 are substantially greater than they are today (Fig 6). Neither scenario comes close to creating the turn around in the global profile required.
The UK government has taken a lead on this issue and has agreed a target for the reduction of greenhouse gas emissions of 60% by 2050 - predicated on a stabilisation target of doubled carbon dioxide concentrations together with a recognition that developed countries will need to make greater reductions to allow some headroom for developing countries. Economists in the UK government Treasury Department have estimated the cost to the UK economy of achieving this target. On the assumption of an average growth in the UK economy of 2.25 % p.a., they estimated a cost of no more than the equivalent of 6 months’ growth over the 50 year period. Similar costs for achieving stabilisation have been estimated by the IPCC.
The effect of a reduction of 60% on average by developed countries is shown in Fig 6(c) together with a scenario for developing countries that increases by 1% p.a. until 2030 followed by level emissions to 2050. For this the 500 ppm curve is approximately followed but for developing countries to be satisfied with such a modest growth presents a very large challenge. Even more challenging for both developed and developing countries would be the measures required to stabilise at 450 ppm (Fig 6(d). Governor Schwarzenegger of California has begun to address this challenge by proposing an even more demanding reduction target of 80% by 2050.
Can we wait and see?
In order to achieve reductions on the scale that is required to stabilize carbon dioxide concentrations, large changes will have to occur in way we use energy (through energy efficiency improvements) and generate it (through moves to energy sources with zero or low carbon emissions). But how urgent are the changes required. It is sometimes suggested that we can ‘wait and see’ before serious action is needed. This is an area where policy needs to be informed by the perspective from science.
There is a strong scientific reason for urgent action. Because the oceans take time to warm, there is a lag in the response of climate to increasing greenhouse gases. So far we have only experienced a small part of the climate response to the greenhouse gas emissions that have already occurred. If greenhouse gas emissions were halted tomorrow, climate impacts much greater than we have so far experienced but to which we are already committed will be realized over the next 30 years and more into the future . Further emissions from now on just add to that commitment. It is for this reason that the June 2005 statement from the world’s major science academies urges all nations , ‘to take prompt action to reduce the causes of climate change and adapt to its impacts’ and to ‘identify cost-effective steps that can be taken now to contribute to substantial and long-term reduction in net global greenhouse gas emissions, recognizing that delayed action will increase the risk of adverse environmental effects and will likely incur a greater cost.’
Two further reasons can be identified for urgent action. One is economic. Energy infrastructure, for instance in power stations also lasts typically for 30 to 50 years. As was stated by the leaders of the G8 countries meeting at Gleneagles in the UK earlier this month , We face a moment of opportunity. Over the next 25 years, an estimated $16 trillion will need to be invested in the world’s energy systems. According to the IEA, there are significant opportunities to invest this capital cost-effectively in cleaner energy technologies and energy efficiency. Because decisions being taken today could lock in investment and increase emissions for decades to come, it is important to act wisely now.
A third reason is political. Countries like China and India are industrialising very rapidly. I heard a senior energy adviser to the Chinese government speak recently. He said that China by itself would not be making big moves to non fossil fuel sources. When the developed nations of the west take action, they will take action - they will follow not lead. China is building new electricity generating capacity of about 1 GW power station per week. To move the world forward we have to be seen ourselves to be moving.
The UK and Climate Change
I would like to add a few remarks about the UK and climate change. It was Prime Minister Margaret Thatcher who in 1988, speaking as a scientist as well as a political leader, was one of the first to bring the potential threat of global warming to world attention. Subsequent UK governments have continued to play a leading international role in this issue. This year, Prime Minister Tony Blair has put climate change at the top of his agenda for his presidency of the G8 and the EU.
This international activity has brought the realisation within the UK government that a big environmental issue such as climate change needs to be brought much closer to the centre of the government machine. For instance, Gordon Brown, UK’s Chancellor of the Exchequer has clearly stated the importance of addressing the economy and environment together. In a recent speech he said , ‘Environmental issues - including climate change – have traditionally been placed in a category separate from the economy and from economic policy. But this is no longer tenable. Across a range of environmental issues –from soil erosion to the depletion of marine stocks, from water scarcity to air pollution – it is clear now not just that economic activity is their cause, but that these problems in themselves threaten future economic activity and growth.’
The need for leadershipWe, in the developed countries have already benefited over many generations from abundant and cheap fossil fuel energy – although without realising the potential damage to the climate and especially the disproportionate adverse impacts falling on the poorer nations. The Framework Convention on Climate Change (FCCC) recognized the particular responsibilities this placed on developed countries to be the first to take action and to provide assistance (e.g. through appropriate finance and technology transfer) to developing countries for them to cope with the impacts and to develop cost effective sources of energy free of carbon emissions. The moral imperative created by these responsibilities is reflected in the statement on climate change made by the leaders of the G8 countries meeting at Gleneagles in the following paragraph , ‘It is in our global interests to work together, and in partnership with major emerging economies, to find ways to achieve substantial reductions in greenhouse gas emissions and our other key objectives, including the promotion of low-emitting energy systems. The world’s developed economies have a responsibility to act.’
People often say to me that I am wasting my time talking about Global Warming. ‘The world’ they say ‘will never agree to take the necessary action’. I reply that I am optimistic for three reasons. First, I have experienced the commitment of the world scientific community (including scientists from many different nations, backgrounds and cultures) in painstakingly and honestly working together to understand the problems and assessing what needs to be done. Secondly, I believe the necessary technology is available for achieving satisfactory solutions. My third reason is that, as a Christian, I believe God is committed to his creation and that we have a God-given task of being good stewards of creation – a task that we do not have to accomplish on our own because God is there to help us with it. As a recent statement on climate change by scientific and religious leaders in the U.S. says : ‘What is most required at this moment … is moral vision and leadership. Resources of human character and spirit – love of life, far sightedness, solidarity – are needed to awaken a sufficient sense of urgency and resolve.’
In my work with the IPCC I have been privileged to work with many climate scientists from the USA who are world leaders in their field. The USA is also a world leader in the technologies aimed at reducing greenhouse gas emissions. But science and technology are only part of what is required. Mr Chairman, the moves recently made by the Senate to develop a strategy for addressing the issue of human induced climate change are of great importance. Is it too much to hope that they are the start of a bid for leadership by the US in the wider world as all countries - both developed and developing – set out to meet this challenge together?
Sir John Houghton was co-chairman of the Scientific Assessment for the IPCC from 1988-2002. He was previously chairman of the Royal Commission on Environmental Pollution (1992-1998), Chief Executive of the UK Meteorological Office (1983-1991) and Professor of Atmospheric Physics, University of Oxford (1976-1983). He is currently chairman of the John Ray Initiative, a Trustee of the Shell Foundation and Honorary Scientist at the Hadley Centre.
Captions to Figures
Fig 1. Concentration of carbon dioxide in the atmosphere from 1000 AD and projected to 2100 under typical IPCC scenarios .
Fig 2. Variations of the average near surface air temperature: 1000-1861, N Hemisphere from proxy data; 1861-2000, global instrumental; 2000-2100, under a range of IPCC projections with further shading to indicate scientific uncertainty .
Fig 3. Land affected in Bangladesh by various amounts of sea level rise.
Fig 4. Global emissions of carbon dioxide from fossil fuel burning (in billions of tonnes of carbon) up to 1990 and as projected to 2100 under World Energy Council scenarios , A’s and B’s with various ‘business as usual assumptions’ and C for ‘ecologically driven scenario’ that would lead to stabilisation of carbon dioxide concentration at about 450 ppm.
Fig 5. Carbon dioxide emissions in 2000 per capita for different countries and groups of countries .
Fig 6. Carbon dioxide emissions from fossil fuel burning and profile leading to stabilisation at 500 ppm (a, b and c) and 450 ppm (d). Emissions data from International Energy Agency scenarios ; reference (a), alternative (b) for developed countries (red) and developing (blue). For (c) and (d) see text.
Witness Panel 2
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Dr. W. David Montgomery
Witness Panel 2
Dr. W. David Montgomery
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Mr. Jason Grumet
Bipartisan Policy CenterWitness Panel 2
Mr. Jason Grumet
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Dr. Richard Morgenstern
Witness Panel 2
Dr. Richard Morgenstern
