Natural greenhouse effect

Carbon dioxide is a major greenhouse gas within the atmosphere. Water vapour is a greater contributor to the natural greenhouse effect (55-70% of the total radiative absorption compared to COj s 25%). However, the large inherent variability in atmospheric water vapour compared to the anthropogenically... 

Water vapor is the most abundant of the greenhouse gases and is the dominant contributor to the natural greenhouse effect. About 99 percent of all the moisture in the atmosphere is found in the troposphere, which extends about 1(1 to 16 kilometers above sea level. Only about one-tliird of the precipi-... 

Although it is one of the smallest reservoirs in terms of water storage, the atmosphere is probably the second most important reservoir in the hydrosphere (after the oceans). The atmosphere has direct connections with all other reservoirs and the largest overall volume of fluxes. Water is present in the atmosphere in solid, liquid, and vapor forms, all of which are important components of the Earth s natural greenhouse effect. Cycling of water within the atmosphere, both physically (e.g. cloud formation) and chemically, is also integral to other biogeochemical cycles and climate. Consult Chapter 17 for more details. 

In summary, in a hypothetical world unperturbed by anthropogenic emissions, the presence of HzO, C02, and, to a lesser extent, 03, CH4, and NzO in the atmosphere leads to a natural greenhouse effect that results in an average surface temperature of about 288 K, rather than 254 K, which is expected in the absence of these gases. 

Without the natural greenhouse effect the temperature would fall to about 18°C below zero. Life as we know it, would be inconceivable, since the average temperature on earth is now about 15°C. 

Likewise, it should be recognized that water vapour, which is present in the atmosphere in far greater amounts than carbon dioxide, is also a potent greenhouse gas - it accounts for at least 60-70% of the natural greenhouse effect. One has only to experience the difference in temperature on a frosty, starlit night in winter from that on a cloudy, overcast night to appreciate the... 

Greenhouse Effect. Selected gases in the lower parts of the atmosphere trap heat and then radiate some of that heat back to Earth. If there was no natural greenhouse effect, the Earth s overall averse temperature would be close to 0 degrees Fahrenheit, rather than the existing 57 degrees Fahrenheit... 

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