Academic journal article The Science Teacher

Carbon Uptake

Academic journal article The Science Teacher

Carbon Uptake

Article excerpt

Globally, irrigation increases agricultural productivity by an amount roughly equivalent to the entire agricultural output of the United States, according to a new University of Wisconsin-Madison (UW-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 from 1998 to 2002, estimating the amount of carbon uptake enabled by relieving water stress on croplands. The results were published in the journal Global Biogeochemical Cycles.

"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.

The study also shows quantitatively that irrigation increases productivity in a nonlinear fashion--in other words, adding even a small amount of water to a dry area can have a bigger impact than a larger amount of water in a wetter region.

"More irrigation doesn't necessarily mean more productivity," Ozdogan says. "There are diminishing returns."

This was already known on the field scale, Ozdogan says, but is true globally, as well. …

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