For centuries, poets and songwriters have raved about them, but do we really know what clouds are? Or more importantly, how they can affect weather and monsoon patterns, and trigger climate change?
As considerable parts of India continue to reel under torrential downpours and resultant floods and devastation, Down To Earth (DTE), the development-environment fortnightly published from New Delhi, has emerged with an analysis of this little known but much talked about phenomena. Well known weather scientist M Rajeevan, who is also the secretary, ministry of earth sciences, writes in the opening piece: "Clouds hold the key to predicting monsoon and climate change, but there is very little we can say with certainty about them. Our understanding of clouds is very rudimentary." Clouds and the climate system: The dual nature Clouds are a key component of the climate system because they help regulate the planet's temperature. Clouds are responsible for both heating up and cooling down the planet, depending on their type and where they are located, says DTE. For instance, when located at lower altitudes, clouds typically contribute to the cooling effect by shielding the planet and reflecting around half of the sunlight that strikes them. It is estimated that if cloud cover were absent and all the water in the clouds existed as water on the earth's surface, the planet would have absorbed 20 per cent more heat than what it does currently. This would have made the earth warmer by about 12oC. But when situated higher up in the atmosphere, they trap the infra-red radiation bouncing off the earth's atmosphere, thus warming the planet to the tune of about 7oC. Point out the magazine's writers: "Understanding this dual nature of cloud is important because it shows how changes in clouds will affect the energy balance and radiation budget of the planet." Pollution, clouds and extreme weather events like lightning Despite incidents of intense storms, cloudbursts and flooding becoming the norm across the world, scientists are finding it difficult to predict them. A consensus has been building up that this failure to predict such extreme weather events could be due to a missing link clouds. Scientists, says the magazine, are now zeroing in on aerosols as the crucial factor in formation and evolution of clouds. Aerosols are tiny microscopic particles that are constantly being released into the atmosphere. These can be natural like dust or human-made, like vehicular exhaust or emissions from power plants. Water vapour condenses on these particles to form cloud droplets. The type of the aerosol and its abundance in atmosphere dictates the behaviour of the cloud. Greater the number of aerosols, larger is the number of cloud droplets. But more cloud droplets do not necessarily mean more rain. As cloud water gets distributed among too many aerosols, they result in larger numbers of small droplets, which do not produce rain. Polluted air, therefore, can suppress rainfall. Polluted clouds are capable of causing greater havoc, say scientists interviewed by DTE. Take the case of lightning. Since the year 2000, over 30,000 have died in India due to lightning strikes making it the leading weather-related cause of death in the country. "A comparison of the regions chronically affected by lightning with an aerosol emission map of India shows a strong correlation," writes the magazine. The maximum number of lightning deaths comes from the Gangetic plains, central India and the Deccan plateau regions that are home to the most polluting industries and burning of waste.