WEB NOTE:  Following is a guest opinion column authored by Christopher J. Anderson, assistant director of the Climate Science Program at Iowa State University, and Peter Thorne, professor and head of occupational and environmental health at University of Iowa. Also contributing to the piece were Neil P. Bernstein, Mount Mercy University; Gregory R. Carmichael, David Osterberg and Jerald L. Schnoor, UI; Laura L. Jackson, University of Northern Iowa; Yogesh Shah, Des Moines University; and Eugene S. Takle, ISU.

The U.S. Senate clarified the state of climate understanding among our politicians through a vote on two "sense of the Senate" amendments. On a vote of 98-1, the Senate passed a resolution stating "climate change is real and not a hoax." However, only the slimmest of majorities (50-49) supported the language "human activity significantly contributes to climate change" (the amendment needed 60 votes to pass).

The same week the Risky Business project released their report on economic risk to the Midwest from climate change, which left unabated would lead to disruptive negative consequences. It concluded Iowa's economy is at greatest risk among Midwest states. Cargill expressed hopes that this report would serve as a "wake-up call to begin having a conversation." The urgent need for climate action expressed in this comment contrasts starkly with the Senate's view.

Because attribution is answerable by scientific investigation, we felt it would be helpful to identify the current state of the science. Climate has in the past evolved in response to solar variation, volcanic eruptions and glacial advances. When the sun brightens or dims, Earth's temperature quickly rises or falls. In contrast, the increasing amounts of anthropogenic carbon dioxide and other greenhouse gases emitted remain in the atmosphere and contribute to warming for hundreds of years.

Climate science has adapted from forensic science fingerprinting techniques to determine patterns of environmental change consistent with climate warming from greenhouse gases and other natural variations. The laws of physics determine that we would expect greenhouse gas emissions to cause the greatest warming in the Arctic, in the winter, and in the lower atmosphere, whereas warming from the sun would produce the opposite results. Observed loss of Arctic sea ice and ice from Greenland confirm that the Arctic is warming at a very high rate. This and other changes we have seen are overwhelmingly consistent with what science tells us about the impact of greenhouse gases, but are not at all consistent with any of the other potential non-human causes that have been proposed.

What does this mean in terms of certainty? Based on a vast literature, the Intergovernmental Panel on Climate Change recently concluded conservatively that they are more than 90 percent confident that human impacts are evident in the temperature record. To put this into a more familiar context, consider a coin. If you were to flip a coin four times, the chances of it coming up heads all four times are only 6 percent (a 94 percent confidence that heads would not occur four times running). That's a large degree of confidence.

Good policy must be based upon good information. Once you know what the facts are, you can make better decisions about what to do, so it seems that everyone is better off if they understand the truth of the situation. We know humans, by adding greenhouse gases to the atmosphere, have altered the climate. The situation calls for a sense of urgency, because climate scientists are even more confident that effects from increased greenhouse gases will intensify and persist for decades. Regardless of what you believe our policy response should be to that information, we urge voters to contact their representatives and encourage them to always use the best available science to inform their decisions.