230 billion tonnes of soil carbon could be released via global warming

Scientists at the University of Exeter warn that a two degree increase in global temperature would release 230 billion tonnes of soil carbon

The University of Exeter led an international study to investigate the sensitivity of soil carbon turnover, in reaction to global warming.

In April, the world stood still. Global economies froze as industries came to a halt, to attempt to bring the 2020 dominating COVID-19 virus under control. As people retreated from public life, the impact was visible on the environment. Dolphins swam in the canals of Venice, and the pollution-clogged skies of cities like Kanpur became clearer than residents could ever remember seeing.

By July, the world began to shake itself awake. Some economies kicked into full-gear, especially in China and several European countries. Throughout that time period, scientists studied the impact of such mass human behaviour change on the environment. The decline in emissions was greater than during the financial crisis of 2008, the oil crisis of the 1979, or even World War II.

Global soils contain two to three times more carbon than the Earth’s atmosphere, which means that when higher temperatures speed up decomposition – the carbon spends less time in the soil. This is also known as soil carbon turnover.

‘Substantial soil carbon losses’

“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 co-author Dr Sarah Chadburn, of the University of Exeter.

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

The “positive feedback” effect

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.

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.

Co-author 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.”

Read the study here.