Food production has grown by leaps and bounds over the last five decades to meet with the demands of a growing population but this appears to significantly contribute to seasonal swings in the levels of carbon dioxide (CO2) in the atmosphere.

Advances in the field of agriculture has resulted in more crops being produced than ever before but a new study suggests that intensive farming is also to be blamed for the changing levels of atmospheric carbon dioxide.

In a new study published in the journal Nature on Nov. 19, Christopher Kucharik, from the Nelson Institute Center for Sustainability and the Global Environment at the University of Wisconsin-Madison, and colleagues has shown that the steep increase in the production of crops that are grown for food is up to 25 percent responsible for the seasonal increase in carbon dioxide.

The findings of the study do not imply that crops add more carbon dioxide, a heat trapping gas attributed as a major contributor of global warming, to the atmosphere.

The fluctuation of carbon dioxide concentration happens because the CO2 that the plants absorb to convert the sun's energy into food during spring and summer are released back into the atmosphere come autumn and winter.

Crops are like a giant sponge that can absorb and release carbon dioxide into the air and because the production of crops in the Northern Hemisphere has grown by 240 percent since the 1960's this CO2-absorbing-sponge has gotten bigger. Thus, it can hold and release more gas.

"Here we use production statistics and a carbon accounting model to show that increases in agricultural productivity, which have been largely overlooked in previous investigations, explain as much as a quarter of the observed changes in atmospheric CO2 seasonality," the researchers wrote.

Kucharik and colleagues also found that while cropland only makes up about six percent of the vegetated areas in the Northern Hemisphere, it is responsible for the 50 percent rise in the seasonality cycle of the greenhouse gas.

"That's a very large, significant contribution, and 2/3 of that contribution is attributed to corn," Kucharik said. "Corn once again is king, this time demonstrating its strong influence on the seasonal cycle of atmospheric CO2."

Another study, also published in the journal Nature on Nov. 19, supports the findings. Atmospheric scientist Ning Zeng, from the University of Maryland, and colleagues also found that agricultural revolution contributes to amplified seasonal swings in carbon dioxide cycles.

"The intensification of agriculture (the Green Revolution, in which much greater crop yield per unit area was achieved by hybridization, irrigation and fertilization) during the past five decades is a driver of changes in the seasonal characteristics of the global carbon cycle," Zeng and colleagues wrote. "Our analysis of CO2 data and atmospheric inversions shows a robust 15 per cent long-term increase in CO2 seasonal amplitude from 1961 to 2010, punctuated by large decadal and interannual variations."

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