08/25/2017

This Is Why When You Talk About Climate Change, You Can’t Ignore Agriculture

Author: Chelsea Harvey | Published: August 23, 2017 

Agriculture has historically released almost as much carbon into the atmosphere as deforestation, a new study suggests — and that’s saying something.

In a paper published this week in Proceedings of the National Academy of Sciences, researchers found that land use changes associated with planting crops and grazing livestock have caused a loss of 133 billion tons of carbon from soil worldwide over the last 12,000 years, amounting to about 13 years of global emissions at their current levels. And at least half of those losses have probably occurred in the last few centuries.

“Historically, I think we’ve underestimated the amount of emissions from soils due to land use change,” said lead study author Jonathan Sanderman, an associate scientist with the Woods Hole Research Center, a climate change research organization based in Massachusetts.

The researchers suggest that the findings could be used to help target the places around the world that have lost the most soil carbon, and where restoration efforts — which aim to help store carbon back in the ground through sustainable land management — might make the greatest difference. It’s a strategy many scientists have suggested could be used to help fight climate change.

“We have known that extensive agricultural practices are responsible for depleting soil carbon stocks, but the full extent of these carbon losses has been elusive,” said soil expert Thomas Crowther, who will be starting a position as a professor of global ecosystem ecology at the Swiss Federal Institute of Technology in Zurich in October, in an email to The Washington Post. “In this study, the authors do a really good job of quantifying how humans have altered the Earth’s surface soil carbon stocks through extensive agriculture, with direct implications for atmospheric CO2 concentrations and the climate.”

Previously, studies on global soil carbon losses have varied wildly in their conclusions, suggesting historical losses of anywhere from 25 billion to 500 billion tons of carbon, Sanderman noted. In general, based on the average findings from multiple studies, scientists have often assumed a total loss of around 78 billion tons, he added.

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