Scientific consensus that humans cause climate change is akin to the scientific consensus that smoking causes cancer, says a report released today by the American Association for the Advancement of Science.
The report, called "What We Know," marks the kickoff of a new AAAS initiative to increase dialogue on the risks of climate change.
"Opinion polls show that more than half of the American public still think that there is a debate over whether climate change is happening or whether it is human-caused," said James McCarthy, a Harvard University oceanographer and co-chairman of the report.
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McCarthy expressed hope that the report, coming from a trusted source -- AAAS publishes the prestigious journal Science -- and written by a group of esteemed American climate scientists, would get across the message that 97 percent of climate scientists are in agreement and that early action is needed on climate change.
"We are speaking in a way that we hope will be heard unambiguously," McCarthy said.
"The people that do question climate science are either for the most part not scientists or scientists who are not informed in this area," he added.
The report offers three key messages on climate change.
One is that it is happening, and humans cause it.
Second, the risks posed by climate change -- particularly by abrupt, unlikely events, like a sudden melting of the ice sheet, leading to rapid sea-level rise -- are high and potentially very damaging.
Third, the sooner society takes action on climate change, the lower the risk and the cost.
"In some of the scenarios where you lose a lot more ice from Greenland that is expected, that would be devastating," said McCarthy.
Headed toward an 8 F rise in warming
Other such low-probability but high-risk scenarios mentioned in the report include ecosystem collapses, destabilization of methane stored in the seafloor and rapid greenhouse gas emissions from thawing Arctic permafrost.
The report also includes information about how continuing high levels of emissions would affect things like heat waves -- a one-in-20-year heat wave would be likely to occur every year.
Also on the high end, if emissions continue on their current path, the globe's temperature would increase by 8 degrees Fahrenheit, according to the report.
And high-end sea-level rise projections are 6 or 7 feet by 2100.
"About 7 to 8 million people in the U.S. live within 6 feet of the local high tide line, and storm surge can extend flooding far beyond the high tide line, as witnessed in Superstorm Sandy," the report states.
Alan Leshner, the CEO of AAAS, said he hopes the report will get across the "core message" on climate change. Many scientists, he said, have been frustrated by the lack of action on climate change.
"A variety of studies have suggested that the origin of the inertia is to some degree ... a result of this belief that there is widespread disagreement among the members of the scientific community. And certainly, among climate scientists, that's not true," said Leshner.
While many other bodies, including the Intergovernmental Panel on Climate Change, have produced consensus reports on climate change scenarios and impacts, Harvard's McCarthy said he hopes the report's clarity and brevity (it is 15 pages long, not including references) will help it break through.
Edward Maibach, an expert in climate change communication and director of the Center for Climate Change Communication at George Mason University, who also advised the AAAS project on communication science, said the report has a chance of changing minds.
"Reports from leading scientific societies can get considerable media attention, and if they do, they can have an impact on what the public and policy makers think, and do," Maibach wrote in an email.
Evidence vs. apathy
In contrast to the IPCC reports, which are hard for the public and policymakers to digest, this report is concise, potentially giving it an advantage, Maibach noted.
"The most effective educational efforts feature simple clear messages, that are repeated often, by a variety of trusted voices," Maibach said.
"The messages in this report are simple and clear. It remains to be seen if they will be repeated often, by AAAS and other trusted science voices in American society."
Additional outreach efforts will follow the report, said McCarthy, including efforts to communicate with the business and political communities.
Rather than arguing over the science of climate change, public discussion should be about actions needed to address it, he said.
"We can debate the policies; we can debate the measures," McCarthy said. "And that's the debate we should be having."