about 440 ppm by 2030 (Figure 1.1), committing the planet to additional warming. These projections are based on estimates that CO2 emissions in China increased at an annual rate of about 3 to 4 percent during the past 10 years (IPCC, 2007a; IEA, 2007), but a subsequent province-based inventory concluded that emissions actually increased at a higher rate of about 10 to 11 percent (Auffhammer and Carson, 2008). For comparison, total fossil fuel emissions from the United States increased by about 11 percent over the entire 10-year period.1 Emissions from a number of other developed countries were also higher than agreed-to targets. These disparities between projected and actual emissions underscore the large uncertainties inherent in projecting CO2 and other greenhouse gas emissions, particularly beyond a decade.
The Intergovernmental Panel on Climate Change (IPCC) projections may have been too conservative in other cases as well. For example, observed increases in surface temperatures and sea level from 1990 to 2007 were in the upper range of IPCC model predic-