Science meets policy in the most important challenge of our time: global warming. Yet even the most basic facts of this issue (e.g., that the world is warming and that human activity is the dominant cause) are obscure to some decision makers who need to understand them. How can climate scientists be more effective at communicating what they know, how they know it, and how sure they are of it?

The need for scientists to communicate more effectively about climate change is urgent. For people to take climate change seriously and support appropriate responses, they need to feel sure it is happening and is caused primarily by humans. But while the rise in global temperature is a fact (see, e.g., Intergovernmental Panel on Climate Change (IPCC) [2007], which calls the warming “unequivocal”), 56% of Americans believe there is a lot of disagreement among scientists about whether global warming is even occurring. And while every authoritative scientific body attributes most of the warming of the past 50 years to human activity [see, e.g., IPCC, 2007; American Association for the Advancement of Science, 2006], only 41% of Americans believe that humanity is the dominant cause (42% believe it is due about equally to natural and human causes), according to an April 2007 poll by ABC News, The Washington Post, and Stanford University.