London, Nov 2 (IANS): An international team of scientists has found 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 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.

The estimated 230 billion tonnes of carbon released at two degrees Celsius warming (above pre-industrial levels) is more than four times the total emissions from China, and more than double the emissions from the US over the last 100 years.

"Our study suggests substantial soil carbon losses due to climate change at only two degrees Celsius warming, and this doesn't even include losses of deeper permafrost carbon," said study co-author Sarah Chadburn from 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.

To address this, the researchers used a new combination of observational data and Earth System Models - which simulate the climate and carbon cycle and subsequently make climate change predictions.

"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.

The models suggest an uncertainty of about 120 billion tonnes of carbon at two degrees Celsius global mean warming.