Image credit: GenBug (Creative Commons)
With all the evidence of human-induced global warming, you'd think it would be good news that some of our activities, like releasing aerosols for example, are also helping to cool the atmosphere. Unfortunately, often the opposite is true. This is starkly illustrated by a new study showing the regional cooling effects of mass irrigation. So why is this a bad thing? The study, published in the Journal of Geophysical Research and authored by M.J Puma and B.I. Cook, both of Columbia University and NASA's Goddard Institute, tracks the impact of irrigation on global climate in the 20th century. Much like cooling off in the sun after a swim, or sweating to release heat, irrigation creates a cooling effect by absorbing some of the sun's radiation and using it to evaporate water, rather than to heat the soil.
The effect is, the authors say, very regionalized and also very temporary—in fact irrigation has little to no impact on climate change on a global level. But in heavily irrigated areas, the actual effect on climate may be even stronger than warming from CO2 and other greenhouse gases.
The trouble is that many of the most heavily irrigated regions in the world, from India's arid Indus River Basin to California's Central Valley, are in severe danger of depleting the very aquifers that farmers rely on. If this happens, these major food growing regions could be hit by the double whammy of massively reduced water resources and a sudden increase in average temperatures.
The study's authors argue that future climate models need to pay close attention to the effects of irrigation in order to get an accurate picture of regional climatic changes. Farmers might do well to start exploring more efficient water use too if they'd like a more gradual transition from these artificially cooled micro-climates to something more resilient.
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