Of Brown Air and White Clouds
I've never been there, but the Maldives sound like paradise. A chain of islands made of coral that grows on the tops of ancient, submerged volcanoes, the Maldives speckle the equator about 400 miles southwest of India. The islands are sandy, sunny, and covered with palm trees, but there's a problem in the air. Actually, the problem is the air, which is often hazy and polluted.
The brown air that sometimes hangs over the Maldives surprised scientists working on the Indian Ocean Experiment, a recent study to see how humans might affect climate by altering clouds. One of the cloud watchers in the Maldives was Glenn Shaw, a professor of physics at the Geophysical Institute, who traveled to the equator along with graduate students Will Cantrell and Barbara Trost. They were among 150 scientists who converged in an area that included the Arabian Sea, much of the Bay of Bengal, and the Indian Ocean surrounding the equator.
The scientists picked the remote area because it's a spot where two great air masses meet-air drawn to the heat of the equator from India and Asia, and air pulled from the direction of the South Pole. The scientists found that hundreds of miles didn't provide much of a buffer from the 2 billion people of Asia and India. The air from the north carried a dense, brownish cloud, full of soot and other gunk from the Asian subcontinent. The cloud sometimes reduced visibility to about six miles. The air from the south was clean and clear, as would be expected from a parcel originating where there are no people or two-stroke engines.
The researchers noticed another striking difference between northern and southern air--the clouds to the north were mostly white, the southern clouds were gray. Shaw said the mostly white clouds were probably enhanced by people.
How can people manipulate clouds? We can run inefficient engines, burn brush, and create dust problems by converting forests into roads or bare fields. Each process releases tiny particulates into the air. These specks can act as "seeds" that water vapor in the atmosphere grasps to form clouds or make existing clouds brighter.
Irish atmospheric physicist Sean Twomey claimed that an increased number of tiny particles means more clouds. Consisting of fine particles that scatter sunlight, these man-seeded clouds tend to be very white. In a process known as the Twomey Effect, these clouds bounce solar radiation back into space before it reaches Earth. Scientists think these clouds are creating patches of artificial cooling around the globe.
Isn't this good news? Can fluffy mirrors in the sky counter the effects of global warming? "You don't want to say it's bad or good," Shaw said. These clouds can cause Earth's precipitation cycle to change. Droughts that happen in normally wet areas and flooding in dry areas may already be the work of artificially enhanced clouds.
Of course, clouds normally form when water vapor condenses on natural particles, often sulfur emitted by microorganisms in the sea. But Shaw says the striking difference between the man-affected and pristine air masses over the Maldives shows that humans are producing more reflective clouds. How those reflective clouds fit into the climate change puzzle is a complicated question, one that interests the people in the Maldives, for whom global warming has some immediate consequences. The high point on the islands is about six feet, and a rise in sea level that might accompany the melting of the world's ice fields could mean the loss of a good hunk of their country.
