Human activities, particularly the combustion of fossil fuels, have made the blanket of green house gases (water vapour, carbon dioxide, methane, ozone etc.) around the earth thicker. The resulting increase in global temperature is altering the complex web of systems that allow life to thrive on earth such as rainfall, wind patterns, ocean currents and distribution of plant and animal species.
Life on the earth is possible by energy from the sun, which arrives mainly in the form of visible light. About 30 percent of the sunlight is scattered back into the space by outer atmosphere and the balance 70 percent reaches the earth’s surface, which reflects it in the form of infrared radiation. The escape of slow moving infrared radiation is delayed by the green house gases. A thicker blanket of greenhouse gases traps more infrared radiation and increase the earth’s temperature.
Human activities that are responsible for making the green house layer thicker are emissions of carbon dioxide from the combustion of coal, oil and natural gas; by additional methane and nitrous oxide from farming activities and change in land use; and by man made gases that have a long life in the atmosphere.
The increase in greenhouse gases is happening at an alarming rate. If the green house gases continue to grow at current rats’ it is almost certain that the atmospheric levels of carbon dioxide will increase twice or thrice from pre-industrial levels during the 21st century.
Even a small increase in earth’s temperature will be accompanied by changes in climate such as cloud cover, precipitation, wind patterns, and duration of seasons. In an already highly crowded and stressed earth, millions of people depend on weather patterns, such as monsoon rains, to continue as they have in the past. Even minimum changes will be disruptive and difficult.
Carbon dioxide is responsible for 60 percent of enhanced greenhouse effect. Humans are burning coal, oil and natural gas at a rate that is much faster than the rate at which these fossil fuels were created. This is releasing the carbon stored in the fuels into the atmosphere and upsetting the carbon cycle- a precise balanced system by which carbon is exchanged between the air, the oceans and land vegetation taking place over millions of years. Currently carbon dioxide levels in the atmosphere are rising by over 10 percent every 20 years.
Cyclones, storm, hurricanes are occurring more frequently and floods and draught are more intense than before. This increase in extreme weather events cannot be explained away as random events. This trend towards more powerful storms and hotter, longer dry periods is predicted by computer models. Warmer temperatures mean greater evaporation, and a warmer atmosphere is able to hold more moisture and hence there is more water aloft that can fall as precipitation. Similarly, dry regions are prone to lose still more moisture if the weather is hotter and hence this leads to more severe droughts and desertification.
Those to suffer most from the climate change will be in the developing world. They have fewer resources for coping with storms, with floods, with droughts, with disease outbreaks, and with disruptions to food and water supplies. They are eager for economic development themselves, but may find that this already difficult process ha become more difficult because of climate change. The poorer nations of the world have done almost nothing to cause global warming yet is most exposed to its effects.