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Are we measuring ruminant methane emissions correctly?

17 January 2020

Researchers at Oxford University have developed GWP*, a new climate metric that accurately measures the impact of methane emissions on global warming – recontextualising the debate surrounding ruminant methane emissions and climate change.

ffinlo Costain, host of FAI Farm’s Farm Gate podcast interviewed Myles Allen and John Lynch from Oxford University to explore their new method of measuring the impacts of methane on climate change. GWP* is a new metric for global warming potential that measures the change in emission rates for methane instead of measuring emissions by volume. According to their research, GWP* gives a more accurate picture of the influence greenhouse gases have on the world’s climate than existing measures, which assign gases a nominal CO2 equivalent number.

Current climate measures, like GWP100, categorise ruminant-emitted methane and agricultural activities among the greatest contributors to climate change. GWP100 reaches this conclusion by comparing the total amount of emissions and extrapolating the potential impacts on the global climate. According to Roland Bonney, co-founder of FAI Farms and Benchmark Holdings plc, many farmers and farm organisations feel unfairly demonised by these conclusions and public reaction to them. Allen and Lynch echo this view and assert that the GWP100 metric doesn’t capture the full relationship between emissions and climate change.

Bonney asserts that raising ruminants sustainably can be part of the solution to climate change. Raising cattle and sheep in a mixed rotation system, ensuring they are grass-fed and that they have access to natural pastureland can reduce greenhouse gas emissions significantly. In his view, how we farm has a greater impact on global climate than what we choose to eat.

The differences between methane and carbon dioxide

Though both methane and CO2 contribute to climate change, they impact global temperatures differently. Humans emit more carbon dioxide than any other greenhouse gas and it remains the largest contributor to climate change. Though some CO2 can be absorbed by the ocean or be fixed in plant biomass, the bulk of human emissions go into the atmosphere. According to Allen, the CO2 left in the atmosphere causes a persistent warming effect over thousands of years, making its impact more cumulative than other gasses. Unless humans ramp up efforts to remove carbon, it will remain in the environment.

In contrast, methane is emitted in smaller quantities. The gas has a stronger warming effect than CO2, but it breaks down quickly. This means that after a few decades, the methane will be out of the atmosphere and any warming affects will cease.

When describing the different impacts of the gases, Lynch compared the impacts of methane emissions to drinking excessively and getting a hangover – the immediate effects will set you back, but as long as you don’t drink to excess again, the pain and nausea will dissipate. Carbon dioxide, on the other hand, is more akin to lead poisoning – exposure will cause immediate negative effects, and sustained exposure will cause significant damage in the future.

Metaphors aside, comparing one tonne of emitted CO2 to one tonne of emitted methane (CH4) doesn’t give researchers an accurate picture of the gases’ warming potential. Allen’s research indicates that for methane to have the same warming effect as CO2, humans would need to increase methane emissions by multiple tonnes per year and maintain that emissions level indefinitely. In his view, it’s more appropriate to compare the emission rates of methane with a single tonne of emitted carbon dioxide – the central aim of the new GWP* measure. The new metric will also give more accurate climate forecasting than the current GWP100 standard.

GWP* appears to capture these subtleties more effectively than GWP100. Researchers at the SRUC found that measuring the warming impact of farms with a traditional carbon calculator overestimated the impact of farm emissions on climate. When they used GWP* to analyse the same farm data however, methane emissions fell by 75 percent, halving the total climate impact of agricultural emissions.

Ruminant methane and GWP*

In Allen’s analysis, methane’s contribution to climate change is historic – we are feeling the effects of methane pulses from 50 years ago when the global ruminant herd increased. Ruminants contribute to global methane emissions as the herd expands. A new source of methane will have a huge effect, but a sustained source won’t be as impactful. If the herd remains stable or declines (which is happening currently), the methane they produce won’t add to the warming that’s already occurred. Allen argues that the methane produced by the world’s ruminants is keeping global temperatures at stasis – it isn’t contributing to warming or cooling either way.

GWP* allows researchers to differentiate between new sources of methane and existing ones, meaning that fluctuations in the global ruminant herd can be accurately accounted for. According to Lynch, analysing discrete methane sources makes GWP* more accurate and prevents overestimates of the gas’s climate effects.

In Allen’s view, removing all ruminants in order to tackle methane emissions wouldn’t provide a huge climate benefit. Culling ruminants would only give the climate a temporary pulse of cooling – a temporary reduction of 0.1 degrees at the absolute maximum. That’s the equivalent of a few years’ worth of warming from CO2 emissions. Instead of focusing solely on ruminant emissions, activists should also account for methane leakages in Britain’s natural gas infrastructure. Both Lynch and Allen agreed that eliminating CO2 emissions would do more to counteract climate change than simply reducing methane produced by ruminants.

Refocusing on carbon

Allen told Costain that though reducing methane would help the climate, tackling carbon emissions from the fossil fuel industry is more pressing. The emissions from this sector are “additional” to the world’s existing carbon cycle and cause present and future warming events. Unless the UK and other countries enact zero net carbon emissions policies, global climate change will continue. Lynch echoed these sentiments, saying that carbon emissions needed to be removed or offset to stabilise global temperatures.

Listen to the Farm Gate podcast with ffinlo Costain here.



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