I am amazed by the recent attention being paid to the issue of a scientific consensus on climate change. Naomi Oreskes wrote an article a few weeks back in Science, claiming that a literature review shows that a central statement of consensus reported in the IPCC is indeed a consensus. Since that article was published, debate and discussion (see here and here) has taken place on, among other things, whether it is in fact a unanimous perspective rather than the overwhelming view of most scientists.

Yesterday Oreskes published an op-ed in the Washington Post repeating her arguments. She writes,

“There is a scientific consensus on the fact that Earth’s climate is heating up and human activities are part of the reason. We need to stop repeating nonsense about the uncertainty of global warming and start talking seriously about the right approach to address it. The scientific consensus is clearly expressed in the reports of the Intergovernmental Panel on Climate Change (IPCC). Created in 1988 by the World Meteorological Organization and the United Nations Environmental Program, the IPCC is charged with evaluating the state of climate science as a basis for informed policy action. In its most recent assessment, the IPCC states unequivocally that the consensus of scientific opinion is that Earth’s climate is being affected by human activities: “Human activities . . . are modifying the concentration of atmospheric constituents . . . that absorb or scatter radiant energy. . . . [M]ost of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.””

I agree 100% with her assertion that we need to “… start talking seriously about the right approach to address it.” But I have a hard time identifying those at the focus of Oreskes’ complaint. Who is it that objects to the IPCC consensus statement? And if these people can be found (one place to look first is climate-related blogs) why do they matter from a policy perspective? I can identify a few influential people who do not seem to be among the dissenters with respect to the IPCC statement Oreskes focuses on.

Bjorn Lomborg: “There is no doubt that global warming is happening or that it is important. Carbon dioxide from burning fossil fuels will increase Earth’s temperature. That is likely to have an overall negative effect.”

Ronald Bailey: “The main greenhouse gas is carbon dioxide which is accumulating in the atmosphere as a result of the burning of fossil fuels. Carbon dioxide levels have increased from 280 parts per million in 1750 to 372 ppm today. Carbon dioxide and other greenhouse gases trap heat as it is being radiated out into space and re-radiate back toward the surface.”

Fred Singer: “In fact, the IPCC statement is in many ways a truism. There certainly must be a human influence on some features of the climate, locally if not globally.”

Patrick Michaels: “It has been known since 1872 that water vapor and carbon dioxide are the principal “greenhouse” gases in the atmosphere, and that increasing their concentration should elevate the temperature in the lower atmosphere. What has been a subject of contention ever since, is the amount and character of the warming.”

George W. Bush: “First, we know the surface temperature of the earth is warming. It has risen by .6 degrees Celsius over the past 100 years. There was a warming trend from the 1890s to the 1940s. Cooling from the 1940s to the 1970s. And then sharply rising temperatures from the 1970s to today. There is a natural greenhouse effect that contributes to warming. Greenhouse gases trap heat, and thus warm the earth because they prevent a significant proportion of infrared radiation from escaping into space. Concentration of greenhouse gases, especially CO2, have increased substantially since the beginning of the industrial revolution. And the National Academy of Sciences indicates that the increase is due in large part to human activity.”

Oreskes is absolutely right that we need to open discussion on climate policy options, because the ones now on the table are not up to the task (e.g., see this report by the Pew Center on Climate Change). But we are fooling ourselves if we think that trying to quiet any dissenting voices on the science of climate change is a prerequisite to action. As Oreskes has written in a recent paper on scientific proof in policy debates, “In recent years, it has become common for opponents of environmental action to argue that the scientific basis for purported harms is uncertain, unreliable, and fundamentally unproven. In response, many scientists believe that their job is to provide the “proof” that society needs. Both the complaint and the response are misguided.”

It may be that because the policy challenges of climate change are so frustrating and difficult, a natural reaction is to disengage from matters of policy and retreat to the familiar comfort of arguing about science. But it is thoughtful discussion of policy that we now need.