The Honorable John McCain
United States Senate
241 Senate Russell Office Building
Washington, D.C. 20510
Dear Senator McCain:
In response to your letter of July 28, 2003, I would like to offer the following responses to your questions regarding the science of climate change. Your original questions are included in italics:
Question 1 -- First, is there a scientific consensus in your atmospheric research community that the earth has been experiencing a warming trend in the last century and that this global climate change would not be expected from the study of climate changes that have occurred in past millennia? What modeling or other evidence supports your conclusion?
There is strong agreement among the vast majority of climate scientists that Earth has been experiencing a warming trend in the last century and that this global climate change would not be expected from the natural variability such as that experienced in past millennia. By climate scientists, I mean scientists who are actually doing climate science, either modeling or observations, and publishing their work in peer-reviewed professional scientific journals. The enclosed article, On Past Temperatures and Anomalous Late 20th Century Warmth, appeared very recently in the scientific publication, Eos, of the American Geophysical Union. The authors are thirteen highly respected scientists from diverse institutions who answer your question unequivocally in the following statement: " the conclusion that late-20th century hemispheric-scale warmth is anomalous in the long-term (at least millennial) context, and that anthropogenic factors likely play an important role in explaining the anomalous recent warmth, is a robust consensus view." The article also provides references to independently developed global climate models from different institutions (e.g. the National Center for Atmospheric Research, the Geophysical Fluid Dynamics Laboratory, the Hadley Centre in the U.K.) that all demonstrate, "that it is not possible to explain the anomalous late-20th century warmth without the contribution of anthropogenic factors."
It is noteworthy that the very recent document, The U.S. Climate Change Science Program-A Vision for the Program and Highlights of the Scientific Strategic Plan, which was transmitted to Congress by the highest levels of the Administration, prominently features a quote from the June 2001 NRC report, Climate Change Science: An Analysis of Some Key Questions: "Greenhouse gases are accumulating in Earth's atmosphere as a result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise."
The best evidence for a scientific consensus is the Intergovernmental Panel on Climate Change (IPCC) process, which is open to all, and all comments are dealt with and addressed with a written record. Skeptics are involved both as authors and reviewers. I know that you are familiar with the IPCC Third Assessment Report. I want to endorse the conclusions of the report as representing the best, most accurate science that the resources of countries around the world are able to produce. Approximately 700 scientists worldwide contribute to the IPCC reports, and another 700 review them. The fact that this number of scientists, working directly in the field of climate and climate change, produce a consensus, policy-neutral document like the IPCC Third Assessment Report of Working Group 1 is an extraordinary achievement in itself and is likely without parallel in any other field of research.
The main observations of the IPCC Report lead, correctly in my view, to the conclusion that the global average surface temperature has increased over the 20th century by about 0.6 degree Centigrade (1.1 degree Fahrenheit), that the increase in temperature in the late 20th century over the Northern Hemisphere is the largest of any century in the past 1,000 years, and that human activity has caused a major percentage of that late century warming. The warming of the planet has caused snow cover to decrease, glaciers to retreat, global average sea level to rise, and ocean heat content to increase. We are entering a climate regime never before experienced by human civilization.
Question 2 -- Second, is the scientific community in agreement that this climate change is due to the accumulation of enormous quantities of greenhouse gases in the atmosphere due to human activities, primarily the burning of fossil fuels?
Yes, as answered above. This is now very widely believed to be so, even among many skeptics, some of who now argue that the warming will be benign. As noted above, it is not possible to explain the anomalous late-20th century warmth without the contribution of anthropogenic factors.
Question 3 -- Third, does the scientific evidence point to the need to take measures to reduce greenhouse gas emissions now and the potential consequences of inaction?
This question is a lot tougher because it brings into play non-scientific issues and issues that I am not an expert in such as economic and other social factors. However, my personal opinion is that we should not wait to act until everything is known about all of these complex issues. The risk of climate change is very real and the peoples of the world, including those in the United States, should adopt a "no-regrets" strategy and take a number of actions to reduce the threat. This would include stabilizing the global population, reducing fossil fuel emissions, emphasizing conservation much more than we do now, developing alternative and renewable energy sources, and many other actions. In my opinion, these actions would be beneficial even without climate change. I believe we can do all of these things without reducing our standard of living. In fact, I believe that we can do these things and actually increase the quality of life in this and other countries.
In my judgment we should, as a nation, show leadership in this area and act not only to reduce the risk, but also to prepare for the unprecedented changes that are already likely to occur because of humanity's previous actions. This is the responsible course of action. Major disruptions to the U.S. agriculture, economy, and quality of life due to imminent climate change are definitely possible, if not likely. And the threat is not just short term; there are very long time scales involved. For example, concentrations of greenhouse gases take 50 or more years to change perceptibly because they depend on accumulated emissions. The oceans respond to atmospheric heating sluggishly and add a delay of 20 years or more, and ice sheets respond on a much longer timescale. Sea level will take centuries to reach a new equilibrium.
Hence, if we wait for proof beyond a shadow of a doubt that the climate has changed for the worse, it will be much too late to do anything about it.
One of the main risks for the United States is that of a massive, persistent drought. As we know from paleoclimate records, such droughts have occurred in the past. Imagine the Dust Bowl in the 1930s, but lasting for many decades, perhaps centuries, and covering most of the nation, from the West Coast to the Mississippi. This is a real risk, especially because of the likelihood of summer continental drought, which is exacerbated by diminished snow pack in spring. Such a change could occur abruptly and would be devastating for the U.S. As you know from the situation in your own state, such drought has been persistent in the Southwest during the past two years, with consequences for water supplies, heat waves and wild fires.
In summary, prudence (the precautionary principle) argues that we should make an honest and good faith effort to slow the rate of change as well as prepare for changes that are likely to occur even if we start acting now. We are entering into the unknown; we have good guesses as to what may occur, but our knowledge is not enough to make really good predictions. I cannot say with certainty that any of the catastrophic changes suggested by many climate models and the paleoclimate record will occur, but likewise nobody can say with any certainty whatsoever that they will not occur. Again, prudence and risk reduction are called for given the scientific evidence that we now have.
I hope the research information and the personal opinions I have offered are of some relevance and assistance as you and Senator Lieberman offer your amendment to the Senate energy bill.
Richard A. Anthes