Not many Ph.D. students expect their research to generate outrage among Washington pundits decades later, but, as it turns out, that's exactly what happened to Stephen Schneider. Back in 1971, Schneider was studying plasma physics at Columbia and moonlighting as a research assistant at NASA's Goddard Institute for Space Studies. There, he co-authored an article for Science arguing that the warming effect caused by rising amounts of carbon-dioxide in the atmosphere would be swamped by the cooling effect caused by aerosol pollution like dust and smoke.
As it turned out, Schneider and his colleagues had made a calculation error--they neglected to account for the fact that aerosols were regional while CO2 was global--and their prediction of global cooling was later shown to be mistaken. Normally, that mistake would be unremarkable--a textbook example of how science advances and corrects its errors. Yet the paper is still, to this day, fodder for conservatives like George Will, who often bring up Schneider's earlier predictions as a reason why we shouldn't believe today's scientific consensus that the Earth is warming.
Nowadays, Schneider is one of the world's most prominent climatologists--in addition to his work as Professor of Biological Sciences and Interdisciplinary Environmental Studies at Stanford, he has been heavily involved in the Intergovernmental Panel on Climate Change (IPCC), a scientific body tasked with assessing the climate risks facing the planet. (Its most recent report, in 2007, concluded that most of the twentieth-century increase in global average temperatures was "very likely" due to human activities, and that world temperatures could rise between 1.1 and 6.4°C during the twenty-first century.) Notably, Schneider is also something of a scientific pugilist, known for his willingness to debate climate deniers and agitate publicly for sharp reductions in global greenhouse-gas emissions.
Schneider, whose new book, Science As A Contact Sport, just came out, sat down with The New Republic recently to talk about the current state of climate science, the difficulties in assessing risk, and how he balances his activist and scientific personas.
Given your early mistake about global cooling, why should we believe that scientists are better now at figuring out climate change?
There’s always the possibility of error. There’s always the possibility you left something out. But what we now have is an accumulated preponderance of evidence and that’s why the confidence is so much higher now than it was then.
And also continued uncertainty.
There is always uncertainty as well, but as scientists we’re always trying to move the needle toward more confidence. More confidence does not mean 100 percent confidence. The only thing the IPCC ever said it was 100 percent confident in was that it has been warming over the last 150 years. Some try to frame climate change by saying that as long as there remain open elements, it isn’t "proved." That’s a fraudulent frame. Nobody in this world--in medicine, investment banking, military security, environment--is ever 100 percent sure of anything in a complex system.
When I’m asked, "What is the probability that the Greenland ice sheet will melt if temperatures rise X degrees?," I speak in percentages. My very good friend and colleague Jim Hansen says, "One degree." I don’t think Jim knows that. I don’t think I know that. The problem is too complicated for us to know that, so I frame it as a risk management problem: One degree? 25 percent chance. Two degrees? 60 percent chance. Three degrees? 90 percent chance. Is that the truth? Of course not. That’s as honest as I can be based on my subjective reading of the evidence. However, just so you don’t think I’m an optimist relative to Jim, I also think there’s a 5 percent chance that it’s already too late.
What are some of the ways the IPCC’s risk assessment changed between 1990, when the First Assessment Report was published, and now?
As lead author on the climate science for 1995’s Second Assessment Report, I said that we needed to start quantifying what we meant by various kinds of uncertainty. What do we mean by "likely." What do we mean by "high confidence"? Well, my colleagues almost bit my head off! "You can’t do that! It’s not real science. Real science is empirical. Real science is modeling." I said, "We’re not doing science, guys. We’re doing science assessment." Most scientists are toilet-trained to do science. That’s okay, but that’s not IPCC’s job. IPCC was not asked by governments to do new science. It was asked to assess the existing literature base for quality and credibility, because there were so many false claims. The coal industry was saying, "Nobody knows anything." Greenpeace was saying, "The evidence is already too much." Scientists were saying, "We don’t know everything, so let’s not say anything." And the governments were saying, "We have to have some idea what the risk is."
You cannot address the problem of what to do, which is risk management, without addressing the problem of risk, which is probability times consequence. The fact that the event is in the future and the probability is subjective does not stop it from being expert. It’s still the judgment of people who understand as much or more than anyone in the world about how that system works. For the Third Assessment Report [in 2001], we were able to get an independent group to write a guidance paper on uncertainty. This was important to me because I knew that if we did not tell governments how likely climate change is, they would not listen to us about doing something about it.
