Irrigation impacts on global carbon uptake

Globally, irrigation increases agricultural productivity by an amount roughly equivalent to the entire agricultural output of the U.S., according to a new University of Wisconsin-Madison study. That adds up to a sizeable impact on carbon uptake from the atmosphere. It also means that water shortages — already forecasted to be a big problem as the world warms — could contribute to yet more warming through a positive feedback loop. The new research quantified irrigation's contribution to global agricultural productivity for the years 1998-2002, estimating the amount of carbon uptake enabled by relieving water stress on croplands. The results published August 25 in the journal Global Biogeochemical Cycles , a publication of the American Geophysical Union. "If you add up all the annual productivity that comes solely due to irrigation, it adds up to about 0.4 petagrams of carbon, nearly equivalent to the total agricultural productivity of the United States," says study author Mutlu Ozdogan , a UW-Madison professor of forest and wildlife ecology and member of the Nelson Institute for Environmental Studies.