Sunday, January 17, 2010

9. The Effects of Carbon Dioxide

Despite the recent finding of the US Environmental Protection Agency, it is absurd to call carbon dioxide a pollutant. It is plant food, an absolute essential for life on this planet. Without it, there would be no plants. Without vegetation, there would be no food for animals higher in the food chain, and no oxygen for them to breathe. Without replenishment by photosynthetic reduction of CO2, mineral oxidation would have depleted atmospheric oxygen long ago.

In the 400 million years since life from the sea colonized the land, the normal CO2 concentration has been 5 to 10 times greater than the value today. By the standards of geologic history, we are experiencing a CO2 drought that was matched only when the atmospheric concentration was depleted by the explosion of plant life in the Carboniferous period (which eventually created deposits of coal, oil and natural gas).

An enhanced level of CO2 is commonly maintained in greenhouses used for agriculture, since it accelerates growth, improves productivity and reduces water requirements (because the pores called stomata on the undersides of leaves shrink when ambient CO2 increases, and this reduces loss of water by transpiration). Because the atmospheric concentration of CO2 is increasing, both native and agricultural plants can now thrive in drier environments, so that, for example, desertification in the southern Sahara has now reversed: vegetation is reclaiming large areas. Biomass is increasing, worldwide, and this sink for CO­2 constitutes negative feedback that helps to stabilize the amount in the atmosphere. The consequences of anthropogenic CO2 thus include a greener planet, increased food production, and a reduced requirement for fresh water for irrigation. Apart from their possible warming effect, these emissions are unequivocally and undeniably beneficial.

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