The Oxford Martin School has just published the latest in its series of “Restatements”, which review the scientific evidence underlying areas of current policy concern and controversy. The latest project looks at the capacity for grassland used for grazing livestock to store carbon.

Restatements are written in policy neutral terms and designed to be read by an informed but not technically specialist audience. Restatements reflect the breadth of opinion on the topic in the scientific community and involve wide consultation with interested stakeholders. They have previously included summaries of the evidence on which policy for bovine TB and neonic insecticides can be built.

This current Restatement, published in Proceedings of the Royal Society B, looks at an important and contested topic that is difficult for policymakers to navigate. There have been claims, on the one hand, that enough carbon can be stored in pastures to balance all other emissions from livestock production, and, on the other, that the carbon storage potential is minimal and easily reversed.

The Restatement summarises the available evidence (particularly as it relates to the UK), indicating where there is a broad consensus but also where there is still scientific uncertainty – it does not attempt to forge a consensus where none exists.

Governments and policymakers have a tough task trying to make informed decisions around the role grassland management, grazing livestock and carbon soil storage can play in mitigating climate change

It shows that much current disagreement can be explained as follows:

• Severely degraded pasture can accumulate carbon rapidly if managed appropriately but this will plateau over time. Extrapolating from accumulation rates measured at different times can be very misleading.
• Soils differ greatly in their physical and chemical properties and this must be taken into account when estimating storage potentials.
• Grazing regimes affect carbon accumulation and there is some evidence that new ideas such as mob-grazing can have positive effects. This is an area where policymakers would benefit from more evidence.
• Carbon stored in grassland soils can easily be lost, for example after ploughing or if over-grazed. If grasslands are to act as carbon stores then measures are needed for their long-term preservation.
• In developing grassland soil carbon policy it is important to consider the emissions from livestock as well as possible indirect effects (for example, reducing stocking density may lead to displaced food production and emissions somewhere else). It is also important to consider the counterfactual: might fewer emissions occur if the land was used in a different way?

Professor Sir Charles Godfray, Director of the Oxford Martin School who convened the study, said:

‘Governments and policymakers have a tough task trying to make informed decisions around the role grassland management, grazing livestock and carbon soil storage can play in mitigating climate change due to the complexity and difficult-to-navigate nature of the current evidence base.

‘It is our hope that this Restatement presents the current evidence in an easy-to-read and policy-neutral manner that will make it easier for policymakers and other relevant stakeholders to understand the strengths and limitations of the science involved and so make more informed decisions.’