The determination of whether or not increased particle concentrations will cause a warming or cooling effect depends on several considerations. Two important factors are the earth's surface albedo and surface water content, which determine how much of the radiation lost to the surface due to absorption and backscatter would have been used for heating if particles were not present. The vertical location of particles is also important. Particles in the stratosphere will result in surface cooling due to attenuation of solar radiation and the fact that heating due to absorption will occur in the stratosphere and have minimal effect on the surface. Possibly the most important factor is the efficiency of atmospheric particles as backscatterers as opposed to their efficiency as absorbers. Unfortunately, this cannot be reliably measured or inferred. The direction of the effect of increased particle loadings on the global climate is uncertain. An increase in the albedo of the earth-atmosphere system would probably lead to surface cooling. However, depending on particle distribution and characteristics, and underlying ground reflectivity, a net global warming may be favored. In fact, Bryson^^ suggests that the atmospheric warming effect of CO2 has been more than offset by the cooling effect of increased particle loading of the atmosphere over the past few decades. The calculations of Rasool and Schneider^? would tend to support this view. However, more recent evidence suggests that the ratio of absorption to back-scatter in atmospheric aerosols is likely to be high and thus they may create a warming rather than a cooling effect.^^ Another viewpoint is that the effect of increased particle loading will be very small^$ on either the increase or the decrease of temperature. The emphasis of researchers today on the CO2 issue rather than the particle issue would tend to support the latter opinion. 2.3 CARBON DIOXIDE The steadily increasing level of carbon dioxide in the atmosphere is a potential cause of near-term global climate change that is currently being given the most attention by investigators. Most of these investigators expect the so-called "greenhouse effect" of CO2 will result in much warmer global temperatures. Depending on the magnitude of the atmospheric response to increased CO2, this warming could have serious implications for future climate and society.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==