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Soil cannot halt climate change

Long-term field experiments at Rothamsted Research, dating back as far as 1843, prove that modern carbon emissions cannot be locked in the ground to halt global warming.

Unique soils data from long-term experiments, stretching back to the middle of the nineteenth century, confirm the practical implausibility of burying carbon in the ground to halt climate change, an option once heralded as a breakthrough.

The findings come from an analysis of the rates of change of carbon in soil by scientists at Rothamsted Research where samples have been collected from fields since 1843. They are published today in Global Change Biology.

The idea of using crops to collect more atmospheric carbon and locking it into soil's organic matter to offset fossil fuel emissions was launched at COP21, the 21st annual Conference of Parties to review the United Nations Framework Convention on Climate Change in Paris in 2015.

The aim was to increase carbon sequestration by "four parts per 1000 (4P1000)" per year for 20 years. "The initiative was generally welcomed as laudable," says David Powlson, a soils specialist and Lawes Trust Senior Fellow at Rothamsted.

"Any contribution to climate change mitigation is to be welcomed and, perhaps more significantly, any increases in soil organic carbon will improve the quality and functioning of soil," he adds. "The initiative has been adopted by many governments, including the UK."

But there have been serious criticisms of the initiative. Many scientists argue that this rate of soil carbon sequestration is unrealistic over large areas of the planet, notes Powlson: "Also, increases in soil carbon do not continue indefinitely: they move towards a new equilibrium value and then cease."

Removing land from agriculture led to large rates of soil carbon increase in the Rothamsted experiments but doing this over large areas would be highly damaging to global food security, record the researchers.

Similarly, they add, returning crop residues to soil was effective at increasing carbon sequestration but, in some countries, this is already done so cannot be regarded as a totally new practice.

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NOTES TO EDITORS

Publication:

Poulton et al., 2018: Major limitations to achieving "4 per 1000" increases in soil organic carbon stock in temperate regions: Evidence from long-term experiments at Rothamsted Research, United Kingdom. Global Change Biology ( open access article)