1940s, growing to $6 billion per year during the 1980s While scientists agree that urban air pollution can and 1990s. The scientists report that most of the in- alter concentrations of greenhouse gases such as ozone crease has been due to societal shifts. The growth of in the troposphere, they have left the complicated population, demographic shifts to more storm-prone chemistry of urban air pollution out of global climate locations, and the growth of wealth have collectively models. "Global-scale models that do not take into ac- made the nation more vulnerable to climate extremes. count urban areas' highly nonlinear atmospheric Worsenin g Urban Air Pollution Not Expected to Increase Global Temperature over Next 100 Years Researchers at the Massachusetts Institute of Tech- Editor's Note: The following nology (MIT) have found that although urban air pol- is an excerpt of the abstract for lution is expected to increase significantly in the the paper "Effects of Topogra- coming century, it will not have a big effect on global phy and Other Factors on Move- temperature change. ment of Lows in the Middle East While there may be temperature increases in cer- and Sudan" by M.G. El-Fandy. tain regions, global mean surface temperature will not go up significantly because of urban air pollution, re- searchers at MIT's Joint Program on the Science and Policy of Global Change wrote in a paper published In the area extending from the Middle East in the 27 September issue of the Journal of Geophysi- to the southern Sudan the pressure distribu- cal Research—Atmospheres. tion generally assumes typical seasonal pat- terns. Apart from winter (December to Using a method that allows global coupled chem- February) the main low-pressure system istry climate models to take urban air pollution into which has a direct control on the weather of account in a new way, MIT researchers found that the area under consideration is an oscillatory compared to a reference run excluding urban air pol- barometric minimum, which during the two lution, the average tropospheric ozone concentration transitional seasons (spring—March to decreases while high concentrations of ozone are pro- May—and autumn—September to Novem- jected in the urban areas. As a consequence of the ber) is centered over the central Sudan, and change in the chemical composition of the tropo- sphere, the lifetime of methane increases. This leads is referred to as the Sudan monsoon low. In to higher ambient methane concentrations, even if October, which represents average conditions emissions are unaltered. As ozone decreases and meth- in autumn, for example, this low normally ane increases, the net effect on the radiative budget of extends to about lat. 16°N, but continues to- the earth is small, because the contributions from these wards north with a small inverted V-shaped two greenhouse gases partially cancel each other out. arm projecting to the northern Red Sea. As winter starts the low acquires a southerly dis- "People thought things would go in this direction, placement and by January, which represents but they couldn't quantify it before," said Monika average conditions in winter, it becomes situ- Mayer, research scientist at MIT's Department of ated near the Abyssinian Lake Plateau. On the Earth and Atmospheric Sciences and lead author on other hand in late spring and early summer the paper, "Linking Local Air Pollution to Global to the low moves from the central Sudan Chemistry and Climate." across Arabia to Persia, and by July it be- Global climate models are used by researchers to comes a part of the Asiatic monsoon low predict future conditions and to aid global policy mat- which extends to the N.E. Sudan. ters such as the Kyoto Protocol. One example is the MIT Integrated Global System Model, which includes an economic development model, a two-dimensional land and ocean resolving interactive chemistry-cli- Bull. Amer. Meteor. Soc., 31, 375. mate model that divides the planet into 24 latitudinal bands, a terrestrial ecosystems model, and a natural emissions model. Bulletin of the American Meteorological Society
Bulletin of the American Meteorological Society – American Meteorological Society
Published: Dec 1, 2000
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