Greenhouse effects and global warming

Effects of Green House Gases

(a) CO₂ fertilization effect: Increase in atmospheric concentration of CO₂ increases productivity of C₃ plants and decreases rate of transpiration due to partial stomatal closure.

(b) Possible Effects of Global Warming

(i) Increasing of global temperature (increased 0.6°C, most of it during last 3 decades) and more extreme climatic conditions [EI Nino effect].

(ii) Warming of troposphere and cooling of stratosphere and thermosphere.

(iii) Global warming will push tropics into temperate areas and temperate areas towards pole (shifting of climatic zones) and higher altitudes in mountains resulting into changed species distribution.

(iv) Melting of ice caps.

(v) Rising of sea level, changes in rainfall pattern.

Control measures -Reduced deforestation, cutting down use of fossil fuel, planting trees, slowing down population growth.

GLOBAL ENVIRONMENT CHANGE

CO₂, CH₄, N₂O and CFCs are radiatively active gases and also called green house gases.

The increased amounts of these gases in atmosphere is affecting the global climate and this phenomenon is known as global climatic change.

I. Green House Gases and Global Warming

(i) Term green house effect was coined by Arrhenius.

(ii) Green house gases trap the long wave radiations. A part of this energy is re-radiated back to the surface of earth. The downward flux of long wave radiation by green house gases is called green house flux.

(iii) The phenomenon of keeping the earth warm due to presence of certain radiatively active gases in the atmosphere is called green house effect, without which the average temperature of earth would have been between -18°C to -20°C rather than present average of 15°C.

Relative contribution of different green house gases to global warming

(iv) The excessive increase in concentrations of these gases in the atmosphere would retain more and more of the IR -radiation (long wave radiations), resulting in enhanced green house effect.

(v) CFC is most effective green house gas (effectiveness is 14,000 times more than CO₂),