International Symposium on
Drylands Ecology and Human Security
Influence of Aerosol Contamination of Stratosphere
V. M. Lelevkin, B.B. Chen & A.K. Tynybekov
At present, in the mountain regions of Tien-Shan and Pamir reduction and vanishing of glaciers is occurring. According to glaciological data, 1081 glaciers disappeared at Pamir and Alai between 1957 and 1990, and 71 glaciers have completely thawed at Zailijsky Ala Tau. The glaciers recede with an average velocity of 8 meters per year. Not only is the linear size of glaciers reduced, but also their volume. This influences significantly river waters, vegetation and Central Asian climate.
There are several reasons for glacier destruction, one of which is the global rise of temperature. According to the World Meteorological Organization experts, during the last decades the increase in temperature of the ground air layer was 0.5°, and in the next 30-50 years it could cause a significant rise in global temperature.
The other reason is connected with the drying of the Aral Sea and the associated intensified wind erosion of the dried bottom. In a dust cloud, the suspended aerosol particles with admixtures of agricultural fertilizers and other components of industrial and home wastes predominate. The dust, lifted into the air, reaches high heights and is transported over significant distances. Dust accumulation on the surfaces of the glaciers leads to their pollution and causes intensive ice thawing. Scientists of St.-Petersburg University tested this hypothesis experimentally, on the basis of the analysis of aerosol samples taken from different glaciers of Pamir and Tien-Shan, near the Aral Sea. The obtained data, however, did not allow them to prove unambiguously the strong influence of Aral Sea drying on dust accumulation on glacier surfaces, though a constant increase of the concentration of NaCl and Ba compounds, characteristic for the seas, has been observed in ice sediments.
The glacier pollutions with dust from weathering belong to natural drivers of thawing. The dust comes from Afghanistan, China and desert regions surrounding Tien-Shan. Much of it is brought by dust storms originating in the deserts of Central Asia.
The existing opinion, that the main reason of climate change is the increased accumulation of greenhouse gases in the atmosphere, is not convincing enough. Recent investigations have shown that the stratosphere aerosol (SA) is one of the basic factors influencing the radiative balance and climate (Chen and Lelevkin, 2000). SA influences systems with high levels of exiting long-wavelength radiation, for example systems with cloudless skies and warm spreading surfaces. Cooling at the expense of aerosol (the albedo effect in the short-wave region of a spectrum) predominates over heating (the greenhouse infra-red effect) for all regions, excluding the polar regions in winter (Chen and Lelevkin, 2000). hi the background phases, the heating effect is observed in the stratosphere during the cold half-year, and the albedo effect is observed in the troposphere. During the warm half-year, predominate cooling of the stratosphere and heating of the troposphere is observed. Estimations of temperature change at the expense of background SA shows a drop of ground temperature in northern regions by 0.16-0.18 °C per year, on the average. In high mountain regions the drop is 0.11-0.13 °C, which compares well to model calculations predicting that the background SA reduces the average global temperature of the ground layer by 0.1 °C.
Up to 20 grams/m2 of dust accumulate on glaciers per year. Natural phenomena such as eruptions of volcanoes, earthquakes, mud flows, dust storms, floods, droughts, as well as anthropogenic catastrophes - nuclear tests, fires at petroleum slits, wood cutting and drying of the Aral Sea - exert a huge influence on the pollution of the atmosphere.