soil and climate change
Soil health and climate change are intrinsically linked. On the one hand, soils are the second largest carbon sink after our oceans, storing 3x more carbon than is found in the atmosphere. On the other hand, rising temperatures and changing precipitation patterns can lead to soil erosion and fertility loss and a decline in soil’s ability to carry out basic ecosystem services.
With climate change a political and scientific priority, scrutiny is growing of soil’s potential role in capturing and storing carbon. This year both the UK Climate Change Committee and the Institute for European Environmental Policy included carbon sequestration among the critical levers required for agriculture to reach net-zero and sharply decrease its emissions by 2050.
But how to define and accurately account for soil’s contribution? The UK Is a signatory to the 2015 4 per 1000 initiative, which is built on the premise that an annual growth rate of 0.4% in soil carbon stocks would significantly reduce CO2 concentration in the atmosphere related to human activities.
The arithmetic behind this claim is disputed, however. Scientists led by Rothamsted Research in the UK, whilst welcoming 4/1000 in principle, argue that the goal is only attainable in certain geographies and circumstances and warn against it being relied upon by policy makers as they look to achieve their carbon reduction goals.
There are a number of factors to consider. For a start, when it comes to carbon storage not all soils are equal. The most carbon-rich soils are peatlands, mostly found in northern Europe, the UK and Ireland, while grassland soils also store a lot of carbon per hectare. Then there is the impact of different farming systems, nitrogen availability, crop selection and cropping practices; and, finally, the rate at which carbon is captured, for how long and how it is accounted for once released.
The challenge of estimating potential gain in carbon is made more acute with the increasing inclusion of soil in carbon emissions trading schemes and carbon taxes. In the US and Canada greenhouse gas reduction credits are being issued to farmers who adopt conservation practices, and there is potential for these schemes to be expanded to offset emissions elsewhere. In the UK upstream soil management practises can go a long way to reducing water contamination, so cutting the energy and therefore the carbon costs for the water companies charged with cleaning it.