What are the main factors for change in our climate ?

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Climate means the average pattern in which weather varies in time. The average is determined over long periods from a month up to decades. The climate of a region depends on the presence or absence of water, the reflection of solar radiation or albedo, the ability to transfer water to the atmosphere (evaporation), the capacity to store heat, and the topography and texture of the region.

Although they constitute only a fraction of the total land area of the earth, metropolitan areas, nevertheless, emit the bulk of all air pollutants. These air .pollutants influence temperature, visibility and precipitation as well as other climatic elements.

We are familiar with the fact/that cities are often warmer than adjacent rural environments. One of the factors leading to the creation of such a ‘microclimate’ is urban heat. This includes the biological heat released by the city population, heat released by some heating devices and industries, automobiles, etc. Other factors are 'accelerated run-off of precipitation instead of absorption and evaporation, altered albedo and heat storage capacity. These result from replacing forests and fields with concrete buildings and consequently greater surface roughness. Human beings thus exert a dramatic influence on local climates.

Another factor involved in climate changes in a city, is the blanket of pollutants that hangs over it. This blanket absorbs a portion of the upward directed thermal radiation emitted by the earth's surface. Part of this radiation is re-emitted by the pollutant, and the other part warms the ambient air, a process that tends to increase the low level atmospheric stability over the city enhancing the probability of higher pollutant concentrations. This, air borne pollutants not only cause a more intense ‘heat bland’ but also alter the vertical temperature structure in a way that hinders their own dispersion.

The excess carbon dioxide, chlorofluorocarbons and methane gas released by man's industrial activities remain trapped in the earth's atmosphere. They prevent the solar heat re-radiated from the earth's surface from escaping into space causing what is known as the ‘Greenhouse Effect’. Over a prolonged period of time, this can result in a substantial rise in earth's mean temperature.

Conversely, an increase in particulate matter in the atmosphere, such as smoke and ash, increases the albedo of the atmosphere. This would mean that more of the incoming solar radiation is being reflected back into space before it reaches the earth's surface. This could result in a drop in the temperature of earth, eventually leading to another glacial period or ice-age for our planet. Prediction of a nuclear winter consequent upon nuclear war is one such scenario predicted by the famous scientist Carl Sagan.


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