Methane: Strategies and Potential for Mitigating Agricultural Greenhouse Gas Emissions

Methane emissions are rising rapidly and accelerating climate change. A new review reveals effective measures that can quickly reduce them.

Methane is a greenhouse gas that traps heat in the atmosphere far more effectively than carbon dioxide – with the small but significant difference that this happens over a far shorter time frame (decades instead of centuries). Cutting methane emissions can thus make a direct and substantial contribution to slowing global warming.

Atmospheric methane concentrations have been rising rapidly since 2007. This is due to emissions caused by human activities, for example agriculture, extracting and burning fossil fuels, and waste management. Most agricultural methane emissions are derived from livestock farming and rice cultivation.

New measurement methods can identify hotspots

This review summarises the rapid advances in direct practical methods to quantify and reduce agricultural methane emissions worldwide. The study identifies three hotspots where methane emissions can be quickly and easily reduced:

Hotspot No. 1 is biogas plants, which produce methane-rich biogas from organic waste. A UK study shows that biogas plants lose 5.2% of their methane production on average, with emission rates ranging from 1.4 to 12.7%. Since these plants are easily controlled and optimised, they are an obvious target for substantial emissions savings.

Hotspot No. 2 is manure management. Manure silos are important methane emitters because they provide an ideal environment for methane bacteria. Tighter coverings, better gas capture, solid-liquid separation or acidification can reduce emissions.

Hotspot No. 3 is the burning of crop waste, stubble and grass. Although very rare in Europe now, burning is widespread in India, Southeast Asia and Sub-Saharan Africa and produces high methane emissions and air pollution linked to 43,000 deaths a year. The waste could be used as animal feed, in biogas plants or for composting instead.

Improvements in rice cultivation…

Rice paddies in the tropics are another major methane emitter. It is estimated that rice cultivation produces 29 million tonnes of methane annually worldwide. Better water management, off-season straw removal and the conversion of straw to biochar could reduce emissions by 22 to 28%.

… and livestock farming

Better ruminant health can reduce methane because productivity increases, i.e. fewer animals are needed to produce the same amount of food. Breeding cattle that emit less methane and using feed additives could also reduce methane emissions.

It is difficult to estimate the global impacts of mitigation measures. According to this review, improvements to biogas plants and livestock management could save 30 to 40 million tonnes of methane annually. Better crop waste management, less burning and improved rice management could save a further 30 million tonnes – a total reduction of up to 60 million tonnes per year by 2050.

Methane destruction is another option: the gas can be converted to CO₂ by oxidation, thereby reducing its global warming potential. This may be feasible in cattle sheds, where high methane concentrations occur. Methane in landfill could be captured and used to generate electricity – especially in the tropics, where it could supplement solar energy.

Contribution to a healthier diet

Finally, changes to the human diet can also make a major contribution to reducing methane emissions. An appropriate diet that meets human nutritional needs can reduce per capita food consumption. This would lead to a reduction both in agricultural production and the amount of waste going to landfill.