A new study by the National Aeronautics and Space Administration (NASA) has revealed that the sunscreen of aerosols over the earth has been thinning since early 1990s.
Aerosols are tiny particles suspended in the air. Some occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray.
Aerosols tend to cause cooling of the Earth's surface immediately below them.
Because most aerosols reflect sunlight back into space, they have a "direct" cooling effect by reducing the amount of solar radiation that reaches the surface. Thus it is an important counter-balance to global warming by greenhouse gases.
The thinning of the "sunscreen" could have given an extra push to the rise in global surface temperatures, it is felt.
In a related study published last week, scientists found that the opposing forces of global warming and the cooling resulting from aerosols could occur at the same time.
"When more sunlight can get through the atmosphere and warm Earth's surface, you're going to have an effect on climate and temperature," said lead author Michael Mishchenko of Nasa's Goddard Institute for Space Studies.
The data used by the study show large, short-lived spikes in global aerosols caused by volcanic eruptions in 1982 and 1991, but a gradual decline since about 1990. By 2005, global aerosols had dropped as much as 20% from the stable level between 1986 and 1991.