Surveys show most Americans believe global warming is real. But many advocate delaying actionuntil there is more evidence that warming is harmful. The stock and flow structure of the climate,however, means “wait and see” policies guarantee further warming. Atmospheric CO_2concentration is now higher than any time in the last 420,000 years, and growing faster than anytime in the past 20,000 years. The high concentration of greenhouse gases (GHGs) generatessignificant radiative forcing that contributes to warming. To reduce radiative forcing and thehuman contribution to warming, GHG concentrations must fall. To reduce GHG concentrations,emissions must fall below the rate at which GHGs are removed from the atmosphere.Anthropogenic CO_2 emissions now exceed removal by about a factor of two. Emissions musttherefore fall by half even to stabilize CO_2 at present record levels. Such reductions greatly exceedthe Kyoto targets, while the Bush administration’s Clear Skies Initiative calls for continuedemissions growth. Does the public understand these physical facts? We report experimentsassessing people’s intuitive understanding of climate change. We presented highly educatedgraduate students with descriptions of greenhouse warming drawn from the IPCC’s nontechnicalreports. Subjects were then asked to identify the likely response to various scenarios for CO_2emissions or concentrations. The tasks require no mathematics, only an understanding of stocksand flows and basic facts about climate change. Overall performance was poor. Subjects oftenselect trajectories that violate conservation of matter. Many believe temperature respondsimmediately to changes in CO_2 emissions or concentrations. Still more believe that stabilizingemissions near current rates would stabilize the climate, when in fact emissions would continue toexceed removal, increasing GHG concentrations and radiative forcing. Such beliefs support waitand see policies, but violate basic laws of physics. We discuss implications for education andpublic policy.
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