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Projects: Observing EarthConnecting Policy and Science: The Intergovernmental Panel on Climate Changeby Richard C. J. Somerville
We climate scientists are planetary physicians. As is true for the findings of medical science, we have learned many things about Earth’s health, but we still have a lot to learn. Our understanding of climate, though incomplete, is already highly useful. For example, we have answered the fundamental question of whether all of us—more than 6 billion humans—by adding to the greenhouse effect, have caused Earth’s atmosphere to warm up in recent decades. The answer is yes. That’s an affirmative answer with 90 percent certainty. Nothing in science can be said to be known with 100 percent certainty—the self-correcting human endeavor of science just doesn’t work that way. To reach 90 percent certainty in any scientific work is remarkable, but the Intergovernmental Panel on Climate Change (IPCC) has reached this unusual state. This international organization of scientists and governments, founded in 1988 under United Nations auspices, is charged with providing objective and transparent assessments of climate change science that will be relevant and useful to policymakers. Over its 20-year history, the IPCC has acquired an enviable reputation for scientific accuracy and integrity. It is widely regarded as the authoritative voice of the climate science research community, and its main findings have been endorsed by national academies of science and scientific professional societies globally. The IPCC is unique. No parallel organization exists in any other domain where science and public policy are so closely intertwined. In recognition of its effectiveness, in 2007 the IPCC shared, with Al Gore, the Nobel Peace Prize. It is the only scientific organization ever to be awarded this high honor. Recognizing Climate Change The IPCC is mandated to be policy-neutral and to refrain from prescribing or advocating policy, which is the prerogative of sovereign governments. It will not be easy to reduce the global dependence on fossil fuels, which provide 80 percent of the world’s energy but are primarily responsible for the increasing levels of greenhouse gases in the atmosphere. As the U.N. climate negotiations in Bali in late 2007 clearly showed, the nations of Earth are still far from agreeing on how to implement and enforce effective policies to stabilize our atmosphere’s chemical composition to avoid dangerous climate change. The report I’ll discuss here is officially known as the Working Group One portion of the Fourth Assessment Report of IPCC. Although it is only part of the full Fourth Assessment Report, I’ll simply call it “the IPCC report.” Working Group One is concerned with the physical science basis of climate change; two other IPCC working groups deal with mitigation of and adaptation to climate change. Two major statements characterize this report: These statements are stronger than those in previous IPCC reports. The first of the four assessment reports appeared in 1990 and contained no such summary statement. The second report, issued in 1995, concluded, “The balance of evidence suggests a discernible human influence on global climate.” The third report, issued in 2001, stated, “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.” In this language, we can track the progression of certainty. The IPCC report also discusses projections of climate change, but in general, the IPCC does not specifically forecast what the climate will do. Instead, it explores a range of hypothetical scenarios in which different rates of population growth, greenhouse gas emissions, and other factors are assumed. Climate models can be run under the different assumptions, so these thought experiments can best be regarded as “what-if” exercises rather than predictions. Furthermore, the IPCC does not itself carry out research. Thus, the projections are a sampling of important results from research carried out by leading climate model groups worldwide and published in the peer-reviewed research literature, then assessed by the IPCC author teams.
Tracking Climate Change From Space • The overall trend in warming per year in the last As for the future, sea level will rise by perhaps 18 to 59 centimeters (7 to 23 inches) during the 21st century, according to projections summarized by the IPCC. This outlook is subject to important uncertainties, however, because scientists cannot yet quantitatively assess the potential for further sea level rise. This is because of ice sheet dynamics that might affect Greenland and Antarctica in particular, dynamics that we don’t understand sufficiently because of the physical processes involved. As a result, we can’t rule out even greater sea level rise. In fact, about 125,000 years ago, the sea level was some 4 to 6 meters higher than today, but relatively high temperatures at that time were sustained for centuries. Over the next two decades, the IPCC projects further climate warming of about 0.2 degrees Celsius (about 0.4 degrees Fahrenheit) per decade. This anticipated warming is relatively independent of which scenario is assumed and continues observed recent trends, which themselves are consistent with earlier IPCC projections. Here are some other anticipated changes. Absolutely Certain Truth? The IPCC report is simply an honest and competent assessment of published peer-reviewed science. It is disconnected from advocacy, spin, and ulterior motives of all kinds. It was prepared in the conviction that sound science can inform wise policy-making. Like medical science, climate science never will be complete, but it is highly useful. The strong reputation of the IPCC derives mainly from the processes involved in drafting its reports, processes that were exceptionally open and transparent. Anyone who wished to review the report in draft form had ample opportunity to do so. According to established IPCC procedure, the 2007 report, which took three years to write, underwent several formal and fully documented expert and government review processes, in which tens of thousands of comments were addressed. All the author responses to each comment are publicly available.
The Summary for Policymakers for Working Group One received unanimous line-by-line approval by more than 100 governments at a week-long plenary session in Paris early in 2007. Governments had the right to refine the wording, and they did this in a harmonious and constructive way, but we scientists who drafted the report determined its substance and ensured consistency with the full report. In the end, the scientists never lost control of the document, and the final version was close to the initial draft. The wide participation of the scientific community, the exceptional level of scientific accuracy, and the absence of policy prescriptions are the characteristics that render the report so powerful. This is precisely why it serves a unique role in informing policymakers as well as others in industry, the media, and the broad public. The writing of this Fourth Assessment Report was done not by any self-selected group with its own agenda but by 152 lead authors chosen from more than 700 nominations from governments. They were diverse in gender and scientific discipline. Fully 25 percent of them had earned their highest degree within 10 years of the time at which they were appointed. They represent new talent, in that 75 percent had not worked on previous IPCC reports. They thus had no selfish motive to defend previous IPCC reports. They provide a global range of viewpoints and experience, and 35 percent were from developing countries and countries with economies in transition. Science Meets Policy Science can contribute to this debate but cannot settle it. The IPCC, as I mentioned earlier, is required by its mandate to be policy-neutral. Neither science nor the IPCC can say that a given atmospheric level of greenhouse gases is safe and another, slightly higher, one is dangerous. It is possible, however, for science, speaking through the IPCC, to provide guidance by suggesting and predicting the severity of climate change, depending on the specific level of greenhouse gases. As a result, various groups, including governments and nongovernmental organizations, have issued statements advocating particular limits on allowable climate change and corresponding greenhouse gas levels. Perhaps the most important public function of climate science with regard to an issue such as global warming is to provide useful input into the policy process. Governments, media, corporations, and individuals should listen to and learn from the science, just as intelligent people listen to their physicians when their health is in question. Sound science can thus inform wise policy-making. Climate is more than just temperature; it is a rich tapestry of interlinked phenomena, multifaceted and inherently complex. The most important effects of climate change will be local, not global, and will not be confined to warming. Global warming is only a symptom of planetary ill health, like a fever. Climate scientists are working to diagnose the causes and help prescribe a cure. Richard C. J. Somerville is a theoretical meteorologist and distinguished professor emeritus at the Scripps Institution of Oceanography at the University of California, San Diego. --------------- The Working Group One IPCC report is available for free download at http://www.ipcc.ch. It is more than 1,000 pages in length and has been published in hard copy by Cambridge University Press. As a coordinating lead author for the IPCC, I helped write it, but in this article I am speaking only for myself and not on behalf of the IPCC. —R. C. J. S.
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