Into the unknown realm
is an emerging branch of climate science to find out ways in which planetary processes can be modified to our advantage. Clouds are one of the most accessible avenues where such changes can be made. The fact that aerosols (microscopic solid or liquid particles floating in air) have the ability to influence cloud properties can be used to make them reflect a greater amount of solar radiation or to bring rain.
Cloud seeding is the manipulation of clouds through the use of aerosols to increase precipitation. The process involves infusing clouds with additional aerosols (the most common is silver iodide) from an aircraft. An increase in aerosols means an increase in the number of particles around which water vapour can condense. Under suitable environmental conditions, this can increase rainfall.
Clouds have another critical role. They regulate the amount of sunlight reaching the earth and the amount of heat earth radiates into space. This dual role can be manipulated through aerosols to mitigate anthropogenic warming. The idea is to whiten clouds by infusing it with aerosols and to increase their reflectivity so that more sunlight is reflected. This requires shooting up jets of seawater sprays into the atmosphere so that the salt aerosol particles can induce whiter and more reflective cloud cover.
Another ambitious proposal involves seeding aerosol particles in the upper troposphere, where icy clouds trap the infrared radiation reflected by earth. The idea is to make this layer thinner so that it allows more infra-red radiation to escape into space.
In India, cloud seeding experiments have yielded mixed results over the past six years. But the technology is being extensively studied in countries like China, which has spent over a billion dollars on rain creation to meet increasing demands for freshwater since 2008.
Geoengineering, however, faces severe criticism as it offers short-term mitigation. It could unleash a cascade of short- and longterm impacts that are beyond imagination because the variables in atmospheric and oceanic sciences are still relatively unknown.