By Alan I. Leshner
Wednesday, December 9, 2009 6:48 PM
Don't be fooled about climate science. In April, 1994 -- long after scientists had clearly demonstrated the addictive quality and devastating health impacts of cigarette smoking -- seven chief executives of major tobacco companies denied the evidence, swearing under oath that nicotine was not addictive.
Now, the American public is again being subjected to those kinds of denials, this time about global climate change. While former Alaska governor Sarah Palin wrote in her Dec. 9 op-ed that she did not deny the "reality of some changes in climate," she distorted the clear scientific evidence that Earth's climate is changing, largely as a result of human behaviors. She also badly confused the concepts of daily weather changes and long-term climate trends when she wrote that "while we recognize the occurrence of these natural, cyclical environmental trends, we can't say with assurance that man's activities cause weather changes." Her statement inaccurately suggests that short-term weather fluctuations must be consistent with long-term climate patterns. And it is the long-term patterns that are a cause for concern.
Climate-change science is clear: The concentration of atmospheric carbon dioxide -- derived mostly from the human activities of fossil-fuel burning and deforestation -- stands at 389 parts per million (ppm). We know from studying ancient Antarctic ice cores that this concentration is higher than it has been for at least the past 650,000 years. Exhaustive measurements tell us that atmospheric carbon dioxide is rising by 2 ppm every year and that the global temperature has increased by about 1.1 degrees Fahrenheit over the past century. Multiple lines of other evidence, including reliable thermometer readings since the 1880s, reveal a clear warming trend. The broader impacts of climate change range from rapidly melting glaciers and rising sea levels to shifts in species ranges.
Thousands of respected scientists at an array of institutions worldwide agree that major health and economic impacts are likely unless we act now to slow greenhouse gas emissions. Already, sea levels are estimated to rise by 1 to 2 meters by the end of this century. Some scientists have said that average temperatures could jump by as much as 4 degrees Fahrenheit if the atmospheric carbon dioxide level reaches 450 ppm. We may face even more dangerous impacts at 550 ppm, and above that level, devastating events. U.S. crop productivity would be affected, while European communities might suffer increased fatalities because of intensely hot summers.
Doubters insist that the earth is not warming. This is in stark contrast to the consensus of 18 of the world's most respected scientific organizations, who strongly stated in an Oct. 21 letter to the U.S. Senate that human-induced climate change is real. Still, the doubters try to leverage any remaining points of scientific uncertainty about the details of warming trends to cast doubt on the overall conclusions shared by traditionally cautious, decidedly non-radical science organizations such as the National Academy of Sciences and the American Association for the Advancement of Science, which represents an estimated 10 million individual scientists through 262 affiliated societies. Doubters also make selective use of the evidence, noting that the warming of the late 1990s did not persist from 2001 to 2008, while ignoring the fact that the first decade of the 21st century looks like it will be the warmest decade on record.
None of these tactics changes the clear consensus of a vast majority of scientists, who agree that the Earth is warming as greenhouse gas levels rise. The public and policymakers should not be confused by a few private e-mails that are being selectively publicized and, in any case, remain irrelevant to the broad body of diverse evidence on climate change. Selected language in the messages has been interpreted by some to suggest unethical actions such as data manipulation or suppression. To be sure, investigations are appropriate whenever questions are raised regarding the transparency and rigor of the scientific process or the integrity of individual scientists. We applaud that the responsible authorities are conducting those investigations. But it is wrong to suggest that apparently stolen emails, deployed on the eve of the Copenhagen climate summit, somehow refute a century of evidence based on thousands of studies.
Palin also errs by claiming that America can't afford to reduce greenhouse gases. The highly regarded Stern Commission revealed that inaction could cost us the equivalent of between 5 and 20 percent of global gross domestic product per year. In contrast, the price of slowing emissions was estimated to be 1 percent of GDP. China, meanwhile, reportedly is investing heavily in clean energy technologies.
Now, policymakers must decide whether to act on the evidence or to avoid facing one of the most crucial issues of our generation.
Alan I. Leshner is the chief executive officer of the American Association for the Advancement of Science and executive publisher of the journal Science.