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96 FUNDAMENTALS OF PHYSICAL GEOGRAPHY Global Warming it will take for earth’s atmospheric system to recover from any change brought about by the Due to the presence of greenhouse gases, the latter. atmosphere is behaving like agreenhouse. The atmosphere also transmits the incoming solar The largest concentration of GHGs in the atmosphere is carbon dioxide. The emission radiation but absorbs the vast majority of long of CO 2 comes mainly from fossil fuel wave radiation emitted upwards by the earth’s combustion (oil, gas and coal). Forests and surface. The gases that absorb long wave radiation are called greenhouse gases. The oceans are the sinks for the carbon dioxide. Forests use CO 2 in their growth. So, processes that warm the atmosphere are often deforestation due to changes in land use, also collectively referred to as thegreenhouse effect. increases the concentration of Co . The time 2 The term greenhouse is derived from the takenforatmosphericCO toa2justtochanges analogy to a greenhouse used in cold in sources to sinks is 20-50 years. It is rising areas for preserving heat. A greenhouse at about 0.5 per cent annually. Doubling of concentration of CO over pre-industrial level is made up of glass. The glass which is 2 transparent to incoming short wave solar is used as an index for estimating the changes radiation is opaque to outgoing long wave in climate in climatic models. radiation. The glass, therefore, allows in Chlorofluorocarbons (CFCs) are products more radiation and prevents the long of human activity. Ozone occurs in the wave radiation going outside the glass house, causing the temperature inside stratosphere where ultra-violet rays convert oxygen into ozone. Thus, ultra violet rays do the glasshouse structure warmer than not reach the earth’s surface. The CFCs which outside. When you enter a car or a bus, drift into the stratosphere destroy the ozone. during summers, where windows are closed, you feel more heat than outside. LargedepletionofozoneoccursoverAntarctica. Likewise during winter the vehicles with The depletion of ozone concentration in the closed doors and windows remain warmer stratosphere is called the ozone hole. This than the temperature outside. This is allows the ultra violet rays to pass through the another example of the greenhouse effect. troposphere. International efforts have been initiated for reducing the emission of GHGs into the Greenhouse Gases(GHGs) atmosphere. The most important one is the TheprimaryGHGsofconcerntodayarecarbon Kyoto protocol proclaimed in 1997. This dioxide (CO 2, Chlorofluorocarbons (CFCs), protocol went into effect in 2005, ratified by methane (CH )4 nitrous oxide (N 2) and ozone 141 nations. Kyoto protocol bounds the 35 (O3).Someothergasessuchasnitricoxide(NO) industrialised countries to reduce their and carbon monoxide (CO) easily react with emissions by the year 2012 to 5 per cent less GHGs and affect their concentration in the than the levels prevalent in the year 1990. atmosphere. The increasing trend in the concentration The effectiveness of any given GHG of GHGs in the atmosphere may, in the long molecule will depend on the magnitude of the run, warm up the earth. Once the global increase in its concentration, its life time in thwarming sets in, it will be difficult to reverse it. atmosphere and the wavelength of radiation The effect of global warming may not be that it absorbs. The chlorofluorocarbons uniform everywhere. Nevertheless, the adverse (CFCs) are highly effective. Ozone which effectduetoglobalwarmingwilladverselyaffect absorbs ultra violet radiation in the the life supporting system. Rise in the sea level stratosphere is very effective in absorbing due to melting of glaciers and ice-caps and terrestrial radiation when it is present in the thermal expansion of the sea may inundate lower troposphere. Another important point to large parts of the coastal area and islands, be noted is that the more time the GHG leading to social problems. This is another moleculeremainsintheatmosphere,thelonger cause for serious concern for the world Reprint 2026-27