Mitigation of greenhouse gas emissions from agriculture: socio-economic costs and impacts

A DEFRA commissioned literature review sought to identify farm-level changes that could reduce CO₂ emissions from agriculture that would be technically feasible, cost effective and acceptable to consumers by 2010.

Socio-economic costs and impacts:

Six farm types were modelled: arable combinable cropping, arable root cropping, pigs and poultry, low yielding dairy and beef, high yielding dairy and beef, upland sheep and beef.
The identified mitigation measures were:
a.) reducing losses from grassland soils by:

• reducing nitrogen inputs as mineral fertiliser and manure
• changes in forage crop and grassland mix
• management of manure application to grassland

b.) reducing losses from animals by:

• changing diet composition, including dietary supplements
• reducing animal numbers
• increasing animal productivity or changing production systems

c.) reducing losses from manures by:

• increased frequency of manure spreading
• changing manure storage sytems
• production of biogas from manure

d.) reducing losses from arable soils by:

• reducing nitrogen inputs
• use of winter cover crops
• changes in crop mix
• irrigation of crops

e.) growing energy crops to offset emissions from the previous components and indirect emissions from the manufacture of inputs.

The dairy / beef farms produced higher baseline emissions than the other farm types. Methane accounted for the majority of emissions on the livestock farms and N₂O on the arable farms. For all farms the quantity of direct CO₂emissions and indirect CH₄ emissions was very small.

The study modelled changes that could achieve a 10% and 40% reduction in GHG emissions from the agricultural sectors.

From the results, there are two win-win situations where changes in farm practice can reduce GHG emissions while increasing net farm margin. One approach is to increase animal productivity – here, a reduction in animal numbers makes a far greater contribution to the reduction in GHG emissions than the changes in feed. On the high yielding dairy farm, these GHG reductions were achieved with no loss of milk yield although levels could not be sustained on the low yielding farm. The other option is reduce nitrogen fertiliser to economically optimal rates.

Results suggest a large degree of uncertainty in absolute level of emissions from the farm types but a high degree of certainty in the optimal adaptations to reduce emissions by a proportion of the total emissions.

If these changes were scaled up to cover the UK agricultural sector as a whole, a 10% reduction in agricultural emissions would cut UK GHGs by 0.6% and if a 40% reduction were achieved it would reduce total UK GHGs by 4.1%. There would be some negative impact on the UK economy as a whole, but the impacts would be very minor: the 10% (0.6%) reduction would lower GDP by 0.002% of total 2010 GDP while the 40% (4.1%) reduction would reduce GDP by 0.077%. The outputs of sectors that supply agriculture are affected by the changes in the reduction scenarios. The fertiliser sector is most affected but the food, pesticides and chemicals sectors also experience a small contraction.