by Nayab Naseer

Created on: March 12, 2009

Cirrus clouds are thin, wispy clouds that usually form above 18,000 feet at all latitudes. These clouds are the most common types of clouds, and constitute around 25 percent of the total cloud cover of this planet. They are especially dense in the tropics, where they constitute around 75 percent of the total cloud cover.

Cirrus clouds are composed of ice crystals and they play two important roles in determining the temperature of the earth. They first trap and reflect back some of the sun's energy, without allowing them to fall on to the earth's surface. This is the albedo effect. Secondly, they trap some of the heat in the form of infra radiation that touches the earth's surface and returns on its way to outer space. This process, known as the greenhouse effect and plays a significant role in warming the earth's atmosphere by around 15 degrees centigrade. Without these cirrus clouds the atmosphere of planet earth would have been 0 degrees centigrade, and thus inhospitable.

However, of late the phenomenon of global warming or simply put, the increased presence of greenhouse gasses in the atmosphere is warming the earth's surface and temperatures are on this rise from the normal. The average temperature of the earth has risen from 15 degree centigrade to 16.1 degree centigrade within the last decade. This has devastating effects on the earth in the form of melting ice caps, rising sea levels, destruction of crops and the likes. The concern now is to reduce the temperature, so that the earth would go back to its normal stage, or at least to limit the damage.

In such a scenario, some atmospheric physicists like David Mitchell propose that by dissipating the cirrus cloud cover, more of suns heat would go out to space, and this would reduce global warming and thus make up for the heating up of the earth by other sources.

The heat of the sun causes the air near the surface to rise, accompanied by water vapor from the oceans. As this moisture-laden hot air meets cooler air at higher altitudes, the moisture present in the air condenses to form tiny water droplets and ice crystals. These water droplets or ice crystals remain suspended in the air and form clouds. When the quantity of such water or ice becomes very heavy, they undergo precipitation and fall down as rain, hail, or snow. Cirrus clouds form in the same way.

The strategy proposed to dissipate cirrus clouds is to seed the existing cirrus clouds with special particles that would grow into large ice crystals. When

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