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. Global soils contain two to three times more carbon than the atmosphere, and higher temperatures speed up decomposition – reducing the amount of time carbon spends in the soil (known as “soil carbon turnover”).
The amount of carbon that is stored in the 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 study, published in the journal Nature Communications, revealed the sensitivity of soil carbon turnover to global warming and subsequently halves uncertainty about this in future climate change projections. “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.
According to the researchers, this effect is a so-called “positive feedback” – when climate change causes knock-on effects that contribute to further climate change. The response of soil carbon to climate change is the greatest area of uncertainty in understanding 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 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.
