Last Friday, the White House posted on its website a six-page criticism of me by the president’s science advisor, John Holdren, expanding on testimony he had given to Congress last week claiming that my views on climate change and extreme weather are outside of "mainstream scientific opinion.” Holdren was specifically responding to Senate testimony I gave last year where I argued that recent extreme weather events, including hurricanes, droughts, floods, and tornadoes, have not increased in recent decades due to human-caused climate change.
In this debate the facts are on my side. The claims I made in my congressional testimony are no different from the ones made by the Intergovernmental Panel on Climate Change ("Long-term trends in economic disaster losses adjusted for wealth and population increases have not been attributed to climate change, but a role for climate change has not been excluded") and broadly supported in the peer-reviewed scientific literature. Even Warren Buffett recently explained that more extreme events haven't affected his insurance investments, but that "I love apocalyptic predictions" because they increase insurance rates, earning him more money. When Holdren links specific weather events to human-caused climate change—such as the California drought or the cold winter—he is exaggerating the state of scientific understandings.
His subsequent attack on me has him serving not as science advisor to the president, but rather wielding his political position to delegitimize an academic whose views he finds inconvenient. We academics wouldn't stand for such behavior under George W. Bush and we shouldn't under Barack Obama either.
Our debate aside, Holdren’s exaggerations on climate science will make it harder, not easier, to establish a bipartisan consensus for action on climate change.
As background, I am an expert on the relationship between natural disasters and climate change. I have published extensively in the scientific, peer-reviewed literature over the past several decades. I believe the basic science of climate change is sound and has been for decades. Humans influence the climate today and will into the future, mainly through the emission of carbon dioxide from the burning of fossil fuels, and this influence poses unknown, but potentially large and irreversible risks in the future. The conclusions lay at the core of the work of the Intergovernmental Panel on Climate Change, which despite a few missteps along the way, has well-summarized these fundamental understandings.
Moreover, I have argued for nearly two decades that stronger policy action is needed by nations to both mitigate and adapt to climate change. I have called for a carbon tax linked to greater government spending on energy technology innovation. And I have supported what President Obama has done to combat climate change, including stronger regulations on efficiency, power plants, and his funding for energy innovation and investment overseas.
Why, then, am I being attacked by the White House science advisor as outside the scientific mainstream?
Because I have also argued against exaggerating the relationship between climate change and extreme weather. While politicians and environmental advocates routinely attribute natural disasters with human-caused climate change, the uncomfortable reality is that such attribution remains speculative. There is not yet a scientific basis for making such a connection. That is not an argument against taking action, but it is an argument for accurately representing the science.
Start with drought. According to the U.S. Climate Change Science Program, drought has, “for the most part, become shorter, less frequent, and cover a smaller portion of the U.S. over the last century. The main exception is the Southwest and parts of the interior of the West, where increased temperature has led to rising drought trends.” Globally, according to the IPCC in its special report on extreme events, “There is medium confidence that since the 1950s some regions of the world have experienced a trend to more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, for example, in central North America and northwestern Australia.”
A new review paper just out by a team of drought experts from around the world, and who hold a range of views on climate change and drought, explained many of the complexities, “How is drought changing as the climate changes? Several recent papers in the scientific literature have focused on this question but the answer remains blurred.”
And it’s not just drought. It is wrong to claim that disasters associated with hurricanes, tornadoes, or floods have increased on climate timescales either in the United States or globally. Hurricanes have not increased in the U.S. in frequency, intensity, or damage since at least 1900. The same holds for tropical cyclones globally since at least 1970 (at which point the data became available to allow for a global perspective).
Floods in the U.S. have not increased in frequency or intensity since at least 1950. Indeed, flood losses as a percentage of U.S. GDP have dropped by about 75 percent since 1940. At the global scale there is a similar lack of evidence for upwards trends in floods. Tornadoes have not increased in frequency, intensity or normalized damage in the U.S. since 1950, and there is some evidence to suggest that they have actually declined.
If this comes as a surprise to anyone it is because of the tendency by campaigners to cherry-pick details, obscure the larger context, and, ironically enough, attack as "deniers" anyone who disagrees.
A considerable body of research projects that various extremes may become more frequent and/or intense in the future as a direct consequence of human-caused climate changes. However, our research, and that of others, suggests that assuming that these projections are accurate, it will be many decades, perhaps longer, before the signal of human-caused climate change can be detected. Extremes are by definition rare events, and for that reason they are just not the best place to be looking for, or expecting to see, the consequences of climate change today.
Climate change is an important issue that will be managed for decades and centuries to come, making accurate representation of climate science by scientists and government officials crucial to maintaining public trust. Exaggerations by advocates of climate action, like those of science advisor Holdren, undermine that trust when they go beyond what the science is telling us. Efforts to quash mainstream, legitimate voices will further undermine that trust.