NEW YORK: Two recent climatologic studies have nearly established that unlike the popular belief that there is global dimming, what is actually happening is a marked increase in the amount of sunlight falling on the Earth's surface.
The two studies, one by a U.S. team and the other Swiss, were reported in the Science magazine and maintain that solar radiation which reaches the surface of the earth has risen over the past two decades.
The data collected after dedicated experiments employing several monitoring stations suggest that the dimming phenomenon reported earlier has been reversed to a certain extent, possibly due to less atmospheric pollution. Proponents of the theory of dimming extend the argument that tiny atmospheric particles, called aerosols, created as a result of human activities, reflect the sunlight back into space, giving an effect of dimming as well as cooling. The scientists in the two teams feel that this activity is in fact countering the efforts of any human-induced greenhouse effect. They say only when humans control the production of aerosols can the impact of global warming be measured.
Dr Martin Wild, who led one of teams -- from the Swiss Federal Institute of Technology in Zurich -- reports that based on scientific data collected from many monitoring stations since 1990, there is an increase in the amount of radiation reaching the Earth. Dr Wild, however, believes that global dimming indeed happened between 1960 and 1990, as found in data collected by earlier monitoring stations and from experiments measuring the rate of evaporation of water.
The second team, from the University of Maryland, the U.S., led by Dr Rachel Pinker, also reported that there was a dimming effect until the 1990s, but subsequently, there is an increase in the radiation amount.
The crucial question raised by climate scientists is -- why has there been a change since the 1990s. Dr Wild explains that since the 1990s, atmosphere has become cleaner largely because of legislative measures initiated by several governments. This has affected the aerosols, leading to a higher amount of heat falling on the Earth.
Dr Wild also believes that the break-up of the erstwhile Soviet Union in 1990 has a significant role in reversing the trend. It is simply because there is lesser output from the highly polluting industries in the dismembered countries.
Elaborate and rigorous studies and painstaking research are needed to establish what type of aerosols is required to contain the Sun's radiation reaching the Earth. Both Dr Wild and Dr Pinker agree on this count.
Climatologists also cite another factor -- changes in cloud cover -- which can also have a very lasting impact. Again detailed studies are required to reach any definite conclusions.
