Global Issues:TROPOSPHERIC AEROSOLS AND RADIATIVE FORCING
Global-mean radiative forcing is a valuable concept for giving at least a first-order estimate of the potential climatic importance of various forcing mechanisms. It is basically a change imposed on the planetary energy balance, that has the potential to alter global temperature. Greenhouse gases, for example, intercept some of the outgoing radiation and thereby act to force the Earths surface to come to a higher equilibrium temperature.
In contrast to greenhouse gases, which act only on outgoing infrared radiation, aerosol particles can influence both sides of the energy balance. Particles of diameters less than 1ìm are highly effective at scattering incoming solar radiation, sending a substantial portion back to space, and consequently cooling the Earth. On the other hand, organic aerosol and soot, generated by biomass burning in the tropics, absorb radiation, thus warming the planet. In addition to the scattering-absorption effect (which is called direct radiative effect), there is the indirect effect. The indirect effect deals with the fact that tropospheric aerosols have a substantial impact on the size distribution of cloud droplets.
The net (direct and indirect) global mean radiative forcing due to the increase in anthropogenic aerosol levels since pre-industrial times is negative and the magnitude is significant. This does not mean, though, that the greenhouse problem doesnt exist, and no control measures on greenhouse gases should be imposed. It only means that the issue of the change of the energy balance of the Earth is far more complex than initially thought, and that substantial research has to be done, in order to quantify the effects of any suggested control measures.
Dr. Christodoulos Pilinis
Environmental Science department
University of the Aegean
Karadoni 17 - Mytilene
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