Achieving net zero – a review of the evidence behind potential carbon offsetting approaches

The report reviews the evidence behind 17 potential carbon offsetting approaches:

• upland peat restoration;
• lowland peat restoration;
• woodland creation;
• grassland management;
• freshwater wetlands – floodplain restoration;
• freshwater wetlands – constructed wetlands management;
• saltmarsh restoration;
• seagrass restoration;
• kelp restoration;
• agricultural soil management practices – arable land;
• agricultural soil management practices – pasture grassland;
• hedges and trees outside woodland;
• enhanced weathering;
• biochar;
• household insulation;
• household low carbon heating;
• other built environment measures (for example, renewable electricity consumption, reducing water consumption, building with timber and low carbon transpor

The highest UK national abatement potential with levels over >10 MtCO2e included four offsetting approaches that are directly linked to soil:

1. Upland peat restoration – Upland peat restoration involves an initial reduction of carbon emissions resulting from halting the loss of carbon from the degraded peat. Once the peatland is restored, it may then revert to being a carbon sink. The UK is one of the top 10 countries in the world in terms of total peatland area.
2. Woodland creation – Major stocks of carbon are in the trunks and roots of trees and in the soils in forests, where it accumulates through the deposition of leaves and other plant matter (in UK woods and forests, up to 75% of the total carbon stock in forests is in soils). Establishing woodland in an appropriate soil type can, therefore, contribute significantly to carbon sequestration and to achieving net zero (in organic soils afforestation can result in carbon emissions).
3. Agricultural soil management practices – pasture grassland – Grasslands account for around 70% of UK agricultural land, so the potential area over which carbon sequestration and storage could occur is considerable. Existing improved grasslands are estimated to account for 274 MtCO2e or 33% of the UK’s total topsoil carbon stock, second only to peat bogs, which have much higher carbon sequestration and storage per hectare but cover a much smaller area than agricultural land. The total carbon stock of agricultural grasslands is also higher than that of arable land. Management measures proposed to enhance the carbon sequestration and storage potential of agricultural grasslands:
   • improved grazing: changes to the timing and intensity of grazing to optimise carbon accumulation in soils
   • fertilisation: for example, by adding manure, which constitutes a direct input of organic carbon as well as boosting plant growth and thereby the returns of plant litter to soil
   • sowing legumes: adds carbon to the soil in the form of the legume root stock and by stimulating grass growth through increased availability of soil nitrogen
   • sowing grasses: including deep-rooted varieties to enhance soil organic material
4. Enhanced weathering – through the addition of silicate rock materials specifically to arable soils.

Restoration of lowland agricultural peatlands can halt the GHG emissions caused by the oxidation of drained and cultivated peat soils and, in some cases, allow them to revert to being a carbon sink. It is also considered to have a high (5-10 MtCO2e) national abatement potential.

Freshwater wetlands – flood plain restoration – The impact of flood plain restoration on the soil carbon balance relative to the current balance on the flood plain isolated from its river will depend on the existing land use on the flood plain and whether this is a source or sink for carbon already. Once hydrological connection is restored, the rate of sediment deposition due to flooding will be the biggest determinant of soil carbon sequestration. Over time, as the flood plain recovers some of its more natural functions, the level of soil saturation and biological influences of developing vegetation will have important impacts over the soil GHG balance. Considered to have moderate national abatement.

Agricultural soil management practices – arable land- Considered to have moderate national abatement. The use of soil carbon practices on agricultural soils, often included as components of ‘regenerative agriculture’, ‘conservation agriculture’ and ‘agroecology’, refers to management measures to increase carbon sequestration on working agricultural soils by:

• maintaining more continuous vegetation cover on the soil
• minimising soil disturbance
• increasing the amount and diversity of organic matter retained in the soil
• maximising nutrient and water use efficiency by plants.

On arable land, key measures include:

• reduced tillage or no tillage: methods of tillage or ploughing where disturbance to soil is minimised
• integration of crop residues to soil
• cover or catch crops
• intercropping
• crop rotations
• addition of manure or other organic matter

These measures increase soil carbon stocks by (1) increasing the extent to which organic matter from plant growth is returned to the soil, and (2) increasing the extent to which organic matter is retained in the soil. They also reduce carbon lost through soil respiration and erosion and through the reduced use of inputs like fertilisers and pesticides.

Biochar refers to charcoal used for soil amendment rather than for fuel. It is produced by heating biomass (to ~300-800°C) in low oxygen conditions, a process called ‘pyrolysis’. Biochar has 3 main potential benefits, and, therefore, has been described by some as a ‘win-win-win solution’:

• carbon sequestration: biochar is generally high in carbon and resistant to microbial decomposition so can sequester carbon in the soil for long periods of time
• soil fertility: biochar can improve soil nutrient and water retention and change soil pH
• biofuel: in addition to biochar, pyrolysis also produces syngas (a mixture of CO, CO2, CH4, H2) and other minor components, which can be used as a biofuel to displace fossil fuels. However, syngas contains tars and carbon monoxide, which limit its use.

It is also considered to have a high (5-10 MtCO2e) national abatement potential.

Recommendations for policy implementation

1. Prioritise the implementation of high-ranking offsetting approaches such as woodland creation and peatland restoration to maximise carbon sequestration (enhance nature-based solutions).
2. Develop policies that support soils management practices that enhance soil carbon storage in both pasture and arable lands.
3. Use the findings to shape the Environment Agency’s carbon offsetting strategy, focusing on effective, scalable, and permanent carbon sequestration methods.
4. Integrate offsetting strategies with broader climate and land management policies to ensure cohesive and sustainable outcomes.

Read the full report

Achieving net zero – a review of the evidence behind potential carbon offsetting approaches