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Pakistan Journal of Biological Sciences

Year: 2005 | Volume: 8 | Issue: 11 | Page No.: 1630-1638
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Research Article

Agriculture and Global Warming: Evapotranspiration as an Important Factor Compared to CO2

F. Azam and S. Farooq

ABSTRACT

Over the past few decades, global warming vis-a-vis elevated CO2 and other greenhouse gases (GHGs) has remained an issue of concern for researchers, environmentalists and policy makers. Fossil fuels have been blamed for most of the rise in atmospheric CO2 over the recent past in spite of the fact that water vapour (WV) is the predominant greenhouse gas (atmospheric concentration of 1-2% i.e., 27-54 times that of CO2 and >95% contribution to greenhouse effect) and mostly of natural origin. Incidentally, most if not all, statistics on GHGs overlooks WV creating the impression of human intervention (anthropogenic) as the dominant contributor to global warming. Similarly, role of evapotranspiration (ET) from the vegetated land in elevating the atmospheric concentration of WV is almost completely overlooked. According to highly conservative estimates ET from agricultural lands is responsible for adding >22x1012 t year-1 to the total atmospheric water of 30-60x012 t. These are astonishing high contributions to atmospheric WV that need to be considered when assessing anthropogenic (agricultural activity is certainly an anthropogenic activity) aspects of global warming. This review takes an account of these factors ultimately suggesting that i) ET is capable of raising the atmospheric WV concentration significantly and ii) evolution and introduction of crop types more efficient in water use may help resolve the problem.
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