A Numerical Experiment on the Effects of Regional Atmospheric Pollution on Global Climate.

Use of a global atmospheric general circulation model to investigate the change in climate caused by the introduction of high concentrations of hygroscopic aerosols into a limited region--roughly, North America. It was postulated that the aerosols would serve as condensation nuclei at lower relative humidity than natural aerosols. The experiment was run simulating 60 days. Values of meteorological properties during this period were compared with those obtained by a control simulation in which the polluted region was absent. Within the polluted region, cloudiness and atmospheric temperatures at the lower level increased while upper-level temperatures decreased. Rainfall was not substantially changed, decreased large-scale rain being compensated by increased convective rain. The pollution causes an enhanced greenhouse effect, and some evidence for convergence associated with the warmed polluted area is shown. The most surprising result is decreased rainfall in tropical South America coupled with the movement of the band of maximum rainfall northward. This causes a dramatic change in rainfall amount and distribution in South America. No compelling physical explanation for this effect was found; it is possibly an artifact of the model. 92 pp. Ref.