The UK ‘4 per mil’ Debate: A review of the British Society of Soil Science 70th anniversary presentations and debate.

“In this blog post, STARS and Nottingham University PhD student Martha Ledger reviews events which took place at the recent BSSS AGM in London.”

On 5th December 2017, the Royal College of Physicians in London played host to the BSSS 2017 annual meeting. Coinciding with World Soil Day 2017, it was fitting that the meeting was centred around a debate concerning the feasibility of the ‘4 per mil’ initiative for UK soils.

The ‘4 per 1000’ (4 per mil) initiative was launched at the COP21 in Paris in 2015. The aim is to slow the increase in atmospheric concentrations of CO2 by annually increasing global soil organic carbon stocks by 0.4% per year. This initiative has received mixed reaction, particularly regarding feasibility and how best to manage UK soils to meet this benchmark.

This was the first time that the Society had held a meeting of members in a debate format. Chaired by Dr Abad Chabbi, four experts were invited to present their perspective on the ‘4 per mil’ initiative as a prompt for debate between delegates and panelists.

Professor Claire Chenu from AgroParisTech opened with an introduction to the ‘4 per mil’ initiative, its scientific foundations and challenges. She stated that the seemingly arbitrary figure (derived by the annual global CO2 emissions from fossil fuels divided by the amount of organic carbon stored in soils globally) should be regarded as aspirational rather than a goal. Instead, we must maintain or increase soil carbon stocks to ensure the initiative is feasible. She recognised the importance of managing agriculture to maximise soil carbon stocks in particular. Therefore, we have direct influence on the stabilisation of soils to reduce risk of erosion, and local implementation means that we are able to account for the diversity of soils that exist across the UK.

Next, Professor Bridget Emmett from the Centre for Ecology and Hydrology outlined her perspective on policy, challenging the top seven common concerns of policy makers and why they must challenge their position. Whilst there are conflicting views on how best to manage UK soils, the Soil Health Enquiry is in fact in agreement about particular issues e.g. measurement of soil organic carbon as the key property for soil health. However, pessimism pervades policy makers, who wish to focus on areas where soil health is most at risk, or believe that the focus on soils for storage and sequestration will be fruitless because soil organic carbon content takes too long to increase. Professor Emmett argues otherwise, arguing that we should not focus on where there are problems because we may miss where problems are developing. Furthermore, she explains that the argument that soil organic carbon is too slow to change and therefore futile is more complex, as carbon can be lost far more rapidly than can be gained. The Countryside Survey have found statistically significant losses in soil organic carbon in the last 10 years, showing that there is urgent need to address the rapidly reducing capacity for carbon storage and sequestration in some of our soils.

Professor David Powlson from Rothamsted Research presented his view on effective land management for achieving the ‘4 per mil’ target. He stated that there are limited options for improving soil properties, however, small increases can have a significant effect. For example, whilst the majority of global soils are not under human management (only 12% are under arable cropland management), certain agricultural techniques (such as mixed farming) can secure and increase soil organic carbon content very effectively. However, there is a conflict of balance between economic gain and maximising the carbon content of soils. If the latter is prioritised, maximum yield cannot be achieved. This is problematic with a growing demand for food across Europe and worldwide. He finished with a concluding statement on the risk of losing credibility if too much is promised from soils towards a climate change mitigation plan. Therefore the ‘4 per mil’ target must be viewed purely as aspirational, not a necessity. Furthermore, we must not forget about the mitigation of other greenhouse gas emissions.

Dr Joanna Clark from University of Reading shed light on the capacity of organic soils to contribute to the ‘4 per mil’ plan. Overall, the accumulation rates needed to meet the target of 0.4% per year are not unfeasible for UK peatlands as they are deep, an effective store and critically, they can grow. She states that the initiative would be more applicable to peat if the aim was to grow peat by 4mm, rather than increase storage capacity by 4 per mil.

The subsequent debate raised issues of how to balance maximising food production versus carbon positive management practices, the issue of pollution swapping (whereby imports from elsewhere might not reflect efforts to increase stocks in a nation’s own territory) and how to incentivise improving soil carbon content for farmers. Overall, the debate was positive and productive, circling around how best to achieve the ‘4 per mil’ initiative for UK soils, rather than dwelling on reasons it may not be achievable.

A vote amongst delegates pre- and post-debate showed that scepticism had developed against the feasibility of achieving the ‘4 per mil’ target in the UK. Nonetheless, the debate has sparked ongoing conversation and interest amongst the UK’s soil community.

A thank you to BSSS for hosting an engaging day of debate and discussion, and for inviting the STARS CDT students to participate.


Author: Martha Ledger

STARS CDT student, University of Nottingham

Twitter: @martha2602