Does Fossil Fuel Combustion Lead to Global Warming?

By acceptance of this article, the publisher and/or recipient acknowledges the U.S. Government's right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper. [Abstract] Tropospheric sulfate aerosols produced by atmospheric oxidation of SO 2 emitted from fossil fuel combustion scatter solar radiation and enhance the reflectivity of clouds. Both effects decrease the absorption of solar radiation by the earth-atmosphere system. This cooling influence tends to offset the warming influence resulting from increased absorption of terrestrial infrared radiation by increased atmospheric concentrations of CO 2. The sulfate forcing is estimated to be offsetting 70% of the forcing by CO 2 derived from fossil fuel combustion, although the uncertainty of this estimate is quite large-range 28 to 140%, the latter figure indicating that the present combined forcing is net cooling. Because of the vastly different atmospheric residence times of sulfate aerosol (about a week) and CO 2 (about 100 years), the cooling influence of sulfate aerosol is exerted immediately, whereas most of the warming influence of CO 2 is exerted over more than 100 years. Consequently the total forcing integrated over the entire time the materials reside in the atmosphere is net warming, with the total CO 2 forcing estimated to exceed the sulfate forcing by a factor of 4 (uncertainty range 2 to more than 10). The present situation in which the forcing by sulfate is comparable to that by CO 2 is shown to be a consequence of the steeply increasing rates of emissions over the industrial era. INTRODUCTION It is generally accepted that fossil fuel combustion is responsible for much of the increase in atmospheric carbon dioxide concentrations above preindustrial values and that this increased CO 2 results in an increased longwave (infrared) radiative forcing of the troposphere that leads to a warming of the earth's surface.{Houghton, 1990 #1} Recently attention has been called to a shortwave radiative forcing by tropospheric sulfate aerosols produced by atmospheric oxidation of SO 2 emitted from fossil fuel combustion. These aerosols scatter solar radiation, increasing clear-sky planetary reflectivity. Increased concentrations of aerosol particles also lead to increased reflectivity of clouds. Both effects are thought to contribute a cooling influence on the planetary energy balance that to some extent offsets the warming influence due to increased CO 2. Accurate knowledge of the net forcing due to fossil fuel combustion is necessary both for interpretation of temperature trends over the …