As the tropical Indian Ocean heats up due to climate change, the authors say, the northern Indian Ocean, which is adjacent to highly-populated regions, is not warming as quickly as the rest of the ocean, resulting in increased drought conditions that could have repercussions for more than 2 billion people in South Asia. These conditions impact a range of industries and resources, from agriculture to freshwater availability.

The culprit behind the changes, the authors argue in a study published in the 15 May 2006, issue of the Journal of Climate, published by the American Meteorological Society (AMS), is an ongoing and intricate clash between air pollution, greenhouse gases and naturally-produced climate changes.

In previous studies they and an international group of colleagues had found that pollution particles called aerosols are masking warming effects from greenhouse gases.

It appears that this whole tropical area is being pulled in different directions. The greenhouse gases are pushing in one direction, warming the ocean and trying to make more rain, and the aerosols are pushing in another direction, toward a cooler ocean and less rain. The net effect is to drive the monsoon rain system away from South Asia into the equatorial and southern oceans.

Some years the aerosols might win, and some years the greenhouse effect may win. We’re concerned that in coming decades the variability between the two will become large and it will be difficult to cope with rapid changes from year to year.

—V. Ramanathan

Pollution haze over Los Angeles. Credit: SIO/UCSD

In addition to Asia, similar pollution, or brown haze, clouds, can be seen in various regions around the world, including over major urban locations such as Los Angeles and Denver in the United States.

Although five to 10 years ago scientists thought about pollution as solely an urban problem, scientists have shown that in a matter of five days, airborne pollutants can travel from China to the United States, and in a matter of three to four days, they can travel from the United States to Europe.

Resources:

• Center for Clouds, Chemistry & Climate