Abstract for presentation at 14th IUAPPA World Congress

The global build up of greenhouse gases (GHGs) such as Carbon Dioxide, Methane and several other GHGs, is the most vexing global environmental issue facing the planet. What is less recognized, however, is a comparably major global problem dealing with air pollution. Until about ten years ago, air pollution was thought to be just an urban or a local problem. But new data have revealed that, due to fast long range transport, air pollution is transported across continents and ocean basins, resulting in trans_oceanic plumes of atmospheric brown clouds (ABCs) containing tiny particles. ABCs intercept sunlight, cause surface dimming, cool the surface and warm the air. In addition they can disrupt regional rainfall patterns and lead to drying, particularly in Africa and Asia. Furthermore, as documented through epidemiological studies , the air pollution in ABCs result in over few million fatalities worldwide. GHGs on the other hand, warm the surface and the atmosphere and make the planet wetter with correlative effects such as melting of glaciers, altering the strengths of storms, increasing sea level among other effects. Recent studies suggest that ABCs mask the surface warming effects of GHGs while at the same time amplifying effects such as increased intensity of rainfall and glacier retreat.
It now seems that the surface cooling effect of ABCs may have masked as much 50% of the global warming due to GHGs. The implication is that elimination of the brown clouds can add another 0.8 C warming to the 0.8 C warming already observed during the last century. Many scientists believe a global warming of about 2 to 2.5 C will lead to unprecedented, if not dangerous climate change. At the same time, absorption of solar radiation by soot contributes to atmospheric warming. Recent measurements with unmanned aircraft and new satellite data reveal that the soot solar heating may be contributing as much greenhouse gases to the warming trends of the tropical free atmosphere (while cooling the surface over the plains) and thus contribute to the retreat of Himalayan glaciers, the major source for several Asian river systems. The surface cooling and atmospheric warming are two sides of the same coin. These new findings on the ABC impacts have major policy implications for water budget of the planet and for climate mitigation actions. The uncertainties in our understanding of these effects are large, but the deeper we delve into the science we are discovering new ways in which human activities are changing the environment and climate, and the ethical and scientific dilemmas are becoming more formidable.