Reducing emissions in agriculture: methane

There is growing pressure on all industries to reduce their carbon emissions. The UK has a net zero deadline of 2050, with an interim carbon reduction target of 78 per cent by 2035. As such, a core part of any businesses sustainability plan will be to understand and reduce their carbon emissions.

But for agriculture, carbon dioxide is only a tiny part of the picture. A much larger proportion of agricultural emissions take the form of methane or nitrous oxide. This blog is the second in a two-part series looking at agricultural greenhouse gas emissions and how to reduce them. In this edition we are looking at methane.

The most common way we interact with methane is as a fuel to heat our homes: methane is the main component of natural gas. It is a molecule made up of carbon and hydrogen, and after carbon dioxide, it’s probably the most talked about of the greenhouse gases.

Like nitrous oxide (discussed in part one here), methane is a potent greenhouse gas. When compared to carbon dioxide, over 100 years its warming effect is at least 28 times greater. But this comparison doesn’t give the full picture.

This type of comparison relies on a measurement called GWP100, which benchmarks the Global Warming Potential (GWP) of a ton of a greenhouse gas against a ton of carbon dioxide over a 100 year period. This works well if the greenhouse gas in question persists in the atmosphere for the 100 years. But the key difference between methane and carbon dioxide is that methane is much shorter lived. It doesn’t remain in the atmosphere for over 100 years: it lasts for around 12 years.

An alternative application of GWPs is a measurement called GWP*. Without getting bogged down in the detail, GWP* accounts for the shorter life-span of climate pollutants such as methane. This is important because it provides a more accurate model of the warming that will be caused and can help countries assess how different mitigation strategies will affect the global target to limit warming to 1.5 degrees Celsius.

With GWP* we can see that reducing methane emissions wouldn’t only prevent additional warming, it could produce a cooling affect. These two characteristics (‘short’ atmospheric lifespan combined with a high warming potential) have brought methane to the forefront of discussions on how we can fight the climate crisis.

While processes which emit methane are naturally found in the environment, for example, in wetland habitats, anthropogenic causes are a key source of methane emissions. Looking at anthropogenic sources of methane emissions, the major causes are the energy sector (for example via leaks in the gas network), and agriculture.

Taking the latest Defra agri-climate data, agriculture was responsible for 47 per cent of annual methane emissions in the UK. The majority of agricultural methane emissions (just under 85 per cent) come from enteric fermentation. The vast majority of this is from cattle, with a smaller proportion from sheep and a very small minority from other animals. The remaining 15.5 per cent of methane emitted by the agricultural sector comes from manure management.

Enteric fermentation is a process by which cows and sheep breakdown their food. Micro-organisms in the rumen degrade carbon from feeds in the absence of oxygen, producing methane as a by-product. This is emitted when the animals burp. Methane is also produced as a by-product when manure decomposes anaerobically (without oxygen).

Livestock diet, health and management can positively impact the methane emissions caused by enteric fermentation. The use of feed additives which inhibit methane production could make a big dent in the amount of methane emitted by the agricultural sector. Various seaweed based additives have performed well in research trials, and some companies are starting to bring such solutions to market. Other innovative technologies to tackle enteric fermentation are also in development. One example is a mask for cattle which oxidise methane at source.

Changing manure management systems also has a role to play in reducing methane emissions from agriculture. Less methane is produced when manure is spread on the land or handled as a solid, as it decomposes aerobically (with oxygen) in these scenarios. Of course, the spreading of excess nutrients on land can cause other pollution issues, so it’s important to have suitable storage facilities that enable manure to be spread in the right place at the right time.

Defra have calculated that the potential greenhouse gas reduction that could be achieved from slurry and manure focussed mitigation methods is 1.5 million tonnes of carbon dioxide equivalent (MT CO2e). Of this 1.5 MT CO2e potential, just 0.1 MT CO2e had been realised as of February 2021.

Such mitigation measures include increasing on farm slurry storage capacity to improve the timing of applications to land, separating the storage of liquid and solid manure, covering solid manure when stored, and storing it on an impermeable base to collect the effluent. The Slurry Investment Scheme is expected to launch later in 2022, which will provide grant funding for improved slurry stores, addressing some of these issues.

The Global Methane Pledge has put methane reduction front and centre in the bid to tackle global warming. The Pledge was one of the main headline grabbers from COP26 in November last year. Over 100 signatories – including the UK, EU and US – have committed to collectively reducing methane emissions by 30 per cent by 2030, on a 2020 baseline.

While many of the no-cost wins to reduce methane emissions are available to the energy industry, we can expect to see the commercialisation of new technologies which will help the agricultural sector to play their part.

As the UK government develop their approach to the Methane Pledge, we will need to see sufficient funding for both the research and development of new technologies, and also to enable farmers to deliver these improvements on the ground.