A recent debate between candidates for Congress in the Wisconsin’s 1st District — U.S. Rep. Paul Ryan, R-Janesville, and Democratic challenger Rob Zerban — included questions about the role of human beings in producing discernible changes in the climate over the last 150 years.
Unfortunately, this question, which is a matter of evidence, analysis and conclusion as all scientific questions are, has become a source of partisan political divide.
The Intergovernmental Panel on Climate Change (IPCC), a scientific body created by the United Nations to inform the UN regarding “scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change,” has issued five reports on this question since 1990.
These reports are a synthesis of many hundreds of peer-reviewed scientific studies on the issue.
With each successive report — they have been issued in 1995, 2001, 2007 and 2014 — the IPCC has increased the certainty of its conclusions.
The language in these reports has changed from “the balance of evidence suggests a discernible human influence on global climate” (1995) to “most of the observed warming is likely (a greater than 66 percent chance) due to human activities” (2001) to warming “over the last 50 years is very likely (a greater than 90 percent chance) due to human activities” to “It is extremely likely (a 95-100 percent chance) that human influence was the dominant cause of global warming between 1951-2010.”
This makes two things quite clear.
First, that scientists are a skeptical bunch and will move toward increased certainty only as evidence accumulates in favor of that conclusion.
Second, that human-induced global warming is a reality with which we must reckon.
During the debate, when asked if humans have a role in global warming, Ryan answered, “I don’t know the answer to that question. I don’t think science does either.”
He may well be correct in his first response, but he is certainly wrong in his second.