Climate and soil carbon

Rich dark soil pouring from hands
Warming of 2°C would release billions of tonnes of soil carbon.

The estimated 230 billion tonnes of carbon released at 2°C warming (above pre-industrial levels) is more than four times the total emissions from China, and more than double the emissions from the USA, over the last 100 years.

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 estimated 230 billion tonnes of carbon released at 2°C warming (above pre-industrial levels) is more than four times the total emissions from China, and more than double the emissions from the USA, over the last 100 years.

Dr Sarah Chadburn, of the University of Exeter, said: "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." This effect is a so-called "positive feedback" – when climate change causes knock-on effects that contribute to further climate change.

Uncertainty 

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.

Rebecca Varney, of the University of Exeter, said: "We investigated how soil carbon is related to temperature in different locations on Earth to work out its sensitivity to global warming."

State-of-the-art models suggest an uncertainty of about 120 billion tonnes of carbon at 2°C global mean warming. The study reduces this uncertainty to about 50 billion tonnes of carbon.

Professor Peter Cox, of Exeter's Global Systems Institute, said: "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."

This Article 

This article is based on a press release from the University of Exeter. This work work was carried-out in collaboration with scientists from the Met Office and institutes in the USA and Sweden. The study, published in Nature Communications, is entitled: "A spatial emergent constraint on the sensitivity of soil carbon turnover to global warming."

MERCH

T-shirt