Farming has changed climate almost as much as deforestation

Agriculturehas contributed nearly as much to climate change asdeforestation by intensifying global warming, according to U.S.research that has quantified the amount of carbon taken from thesoil by farming.

Some 121 billion tonnes (133billion tons)of carbon have been removed from thetop two metres of the earth's soil over the last two centuriesby agriculture at a rate that is increasing, said the study inPNAS, a journal published by the National Academy of Sciences.

It's alarming how much carbon has been lost from the soil.- Jonathan Sanderman, soil scientist

Global warming is largely due to the accumulation of carbondioxide in the atmosphere from such activities as burning fossilfuels and cutting down trees that otherwise would absorbgreenhouse gases such as carbon dioxide.

But this research showed the significance of agriculture asa contributing factor as well, said Jonathan Sanderman, a soilscientist at the Woods Hole Research Center in Falmouth,Massachusetts and one of the authors of the research.

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While soil absorbs carbon in organic matter from plants andtrees as they decompose, agriculture has helped deplete thatcarbon accumulation in the ground, he said.

Widespread harvesting removes carbon from the soil as dotilling methods that can accelerate erosion and decomposition.

"It's alarming how much carbon has been lost from the soil,"he told the Thomson Reuters Foundation. "Small changes to theamount of carbon in the soil can have really big consequencesfor how much carbon is accumulating in the atmosphere."

Sanderman said the research marked the first time the amountof carbon pulled out of the soil has been spatially quantified.

The 121billion tonnesof carbon lost from soil compares toabout 127 billion tonnes(140 billion) tons lost due to deforestation, he said,mostly since the mid-1800s and the Industrial Revolution.

Crop rotation, no-till farming could help

But the findings show potential for the earth's soil tomitigate global warming by absorbing more carbon through suchpractices as better land stewardship, more extensive groundcover to minimize erosion, better diversity of crop rotation andno-till farming, he said.

The world's nations agreed in Paris in 2015 to reduceemissions of greenhouse gases generated by burning fossil fuels
that are blamed by scientists for warming the planet.

President Donald Trump pulled the United States out of thelandmark Paris accord in May, saying it would undermine the U.S.economy and weaken national sovereignty.

Supporters of the accord, including some leading U.S.business figures, said Trump's move was a blow to international
efforts to tackle global warming that would isolate the UnitedStates.