What are some of the reasons why “climate sceptics” dispute the evidence that human activities such as industrial emissions of greenhouse gases and deforestation are bringing potentially dangerous changes to the Earth’s climate?

As the Intergovernmental Panel on Climate Change (IPCC) finalises its landmark report for 2007, we look at 10 of the arguments most often made against the IPCC consensus, and some of the counter-arguments made by scientists who agree with the IPCC.

Adults’ mental models of climate change violate conservation of matter

John D. Sterman, Linda Booth Sweeney

Public attitudes about climate change reveal a contradiction. Surveys show most
Americans believe climate change poses serious risks but also that reductions in greenhouse gas
(GHG) emissions sufficient to stabilize atmospheric GHG concentrations or net radiative forcing
can be deferred until there is greater evidence that climate change is harmful. US policymakers
likewise argue it is prudent to wait and see whether climate change will cause substantial
economic harm before undertaking policies to reduce emissions. Such wait-and-see policies
erroneously presume climate change can be reversed quickly should harm become evident,
underestimating substantial delays in the climate’s response to anthropogenic forcing. We report
experiments with highly educated adults—graduate students at MIT—showing widespread
misunderstanding of the fundamental stock and flow relationships, including mass balance
principles, that lead to long response delays. GHG emissions are now about twice the rate of
GHG removal from the atmosphere. GHG concentrations will therefore continue to rise even if
emissions fall, stabilizing only when emissions equal removal. In contrast, results show most
subjects believe atmospheric GHG concentrations can be stabilized while emissions into the
atmosphere continuously exceed the removal of GHGs from it. These beliefs—analogous to
arguing a bathtub filled faster than it drains will never overflow—support wait-and-see policies
but violate conservation of matter. Low public support for mitigation policies may be based more
on misconceptions of climate dynamics than high discount rates or uncertainty about the risks of
harmful climate change.