Global warming in the twenty-first century: an alternative scenario

Abstract

A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO(2) greenhouse gases (GHGs), such as chlorofluorocarbons, CH(4), and N(2)O, not by the products of fossil fuel burning, CO(2) and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO(2) GHGs has declined in the past decade. If sources of CH(4) and O(3) precursors were reduced in the future, the change in climate forcing by non-CO(2) GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO(2) emissions, this reduction of non-CO(2) GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition-specific long-term global monitoring of aerosol properties.

Figure 1

Estimated climate forcings between 1850 and 2000.

Figure 2

Atmospheric CO₂ and CH₄ observations and range of IS92 scenarios (the solid red line is IS92a).

Figure 3

Growth rates of climate forcings by individual GHGs—CO₂ (A), CH₄ and N₂O (B), and CFC-11 and CFC-12 (C)—based on trace gas data available from the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory.

Figure 4

CO₂ emissions from fuel use (40). The estimate for wood is by N. Makarova (The Rockefeller University; personal communication).

Figure 5

A scenario for additional climate forcings between 2000 and 2050. Reduction of black carbon moves the aerosol forcing to lower values.