Expert Judgments On Climate

The climate models scientists use to formulate Intergovernmental Panel on Climate Change projections, although complex, offer considerable insight about global warming and its likely impacts. But climate science experts’ intuition can often identify potential surprises not readily reflected in climate projections. To capture that knowledge, M. Granger Morgan of the department of engineering and public policy at Carnegie Mellon University and colleagues have conducted surveys of climate scientists. The latest survey reveals that 13 of the 14 experts interviewed believe IPCC’s upper estimate of global warming between now and 2200 is more likely to occur than not if carbon dioxide emissions continue to increase (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.0908906107). The experts believe it’s probable the warming will push Earth’s climate past a “tipping point” in which climate shifts affecting at least half the planet could persist for decades. They also noted that additional research during the next 20 years will only modestly reduce the degree of uncertainty in the projections. “These extensive surveys do a thorough job of getting scientists to carefully think through climate issues and provide their expert opinions,” notes Thomas R. Karl, director of the National Climatic Data Center, who participated in the survey. “If we wait for a fully supported scientific evaluation, we might see a tipping point occur before we are confident enough to say much about it.”