text: There are large uncertainties in underlying assumptions about population growth, economic development, life style choices, technological change, and energy alternatives. . . . Scenarios for future greenhouse gas amounts, especially for CO2 and CH4, are a major source of uncertainty for projections of future climate. . . . The period of record is now long enough to make it useful to compare recent trends with the scenarios. . . . The increase of global fossil fuel CO2 emissions in the past decade, averaging 0.6 percent per year, has fallen below the IPCC scenarios. The growth of atmospheric CH4 has fallen well below the IPCC scenarios. (emphasis added)