Warming of 2°C would unleash 230 billions tons of soil carbon

An international team of scientists has determined that global warming of two degrees Celsius would trigger the release of an estimated 230 billion tons of soil carbon.

The amount of carbon that is stored in soil is two to three times greater than the amount in the atmosphere. As temperatures rise, soil decomposition will be accelerated and the amount of time organic carbon is stored in the soil will be greatly reduced.

The new research substantially reduces the level of uncertainty regarding how future climate change models will represent the sensitivity of soil carbon turnover.

To put the magnitude of the findings into perspective, 230 billion tons of carbon is more than four times the total emissions from China and more than double the emissions from the United States over the last century.

“Our study rules out the most extreme projections – but nonetheless suggests substantial soil carbon losses due to climate change at only 2°C warming, and this doesn’t even include losses of deeper permafrost carbon,” said study co-author Dr. Sarah Chadburn of the University of Exeter.

The link between climate change and soil carbon turnover is an example of a reinforcing or positive feedback loop. Global warming will speed up the loss of carbon, and the subsequent increase in atmospheric CO2 levels will further accelerate global warming.

The loss of carbon from Earth’s soils represents one of the greatest areas of uncertainty when it comes to modeling the carbon cycle in climate change projections.

In an effort to address this uncertainty, the researchers used a new combination of observational data and Earth System Models.

“We investigated how soil carbon is related to temperature in different locations on Earth to work out its sensitivity to global warming,” said study lead author Rebecca Varney.

While current models indicate an uncertainty of about 120 billion tons of carbon at 2°C global mean warming, the new study reduces this uncertainty to about 50 billion tons of carbon.

We have reduced the uncertainty in this climate change response, which is vital to calculating an accurate global carbon budget and successfully meeting Paris Agreement targets,” said study co-author Professor Peter Cox.

The research is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer