The scientists who presented the latest global assessment of climate research on Monday were clear: don’t expect their Intergovernmental Panel on Climate Change (IPCC) to tell us what to do, policy is for policymakers. This week’s publication, by one of three working groups due to report by September 2022, does not even look at the merits of various changes we could make to our economies and ways of life in addressing global warming – that will be for next year.

Yet their compilation of 14,000 scientific publications, establishing the latest knowledge in how our climate is changing and why, gives some clues. Although it is presented as “policy-neutral,” it comes as negotiators are set to meet for the COP26 global conference in Glasgow in November to update commitments from all governments on the action they will take under the 2015 Paris agreement to limit global warming to between 1.5°C and 2°C.

The IPCC’s scientific update also lands on the desk of Ireland’s Climate Change Advisory Council as the Climate Bill passed into legislation last month directs it to draw up the country’s first carbon budget, apportioning how much each sector of the economy can emit of what gases to stay within the limits of existing Irish commitments to EU (and global) targets.

The report’s unequivocal evidence of accelerating, human-caused global warming and its direct link to more severe and more frequent destructive weather events understandably grabs the headlines. Yet buried in the 4,000-page documents also lies the latest assessment of methane, a greenhouse gas that has contributed 0.5°C of the net 1.1°C warming observed in the industrial age to date. 

The report confirms that carbon dioxide is the main culprit, and its concentration in the atmosphere is now “higher than at any time in at least 2 million years”. Yet methane is not far behind, not only in its warming effect but also in the amounts released. After a 156 per cent increase in the presence of the gas in the atmosphere since 1750, methane concentration is now “higher than at any time in at least 800,000 years”.

Some of it is naturally emitted but the rampant increase is, again, due to human activities – mostly leaks from oil and gas extraction, agriculture, and waste decay in landfills. “For present-day emissions, agriculture is the second-largest contributor to warming on short time scales but with a small persisting effect on surface temperature,” the report finds. Cattle, sheep and rice paddies are the main source of agricultural (or biogenic) methane.

In Ireland, the Environmental Protection Agency reports that one quarter of greenhouse gas emissions is under the form of methane, nearly all of it from cattle. This makes agriculture the heaviest emitter in this country, an unusual position shared only with New Zealand among developed nations.

Short time scale, heavy impact

One key phrase in the quote from the IPCC report above is “short time scales”, i.e. around 20 years. During that time, methane has a very strong warming effect, but it also degrades and disappears from the atmosphere, unlike carbon dioxide, which stays on for centuries. 

This has led to recent research into different approaches to so-called short-lived greenhouse gases and hope in the agri-food industry that its biogenic methane emissions, too, could be treated differently, as reflected in the current programme for government and in the new Climate Act.

One side of this discussion has focused on the metric used to measure the global warming potential of each gas, traditionally set over a 100-year time horizon. This is used in calculations such as those from the EPA above. The IPCC has updated these figures with the latest science, showing that 1kg of methane leaked from fossil fuel extraction causes as much warming as 29.8kg of carbon dioxide, while 1kg of agricultural methane is slightly less damaging to the climate with a factor of 27.2.

Still a heavy burden for livestock farming, which has prompted interest for different measurements such as the so-called GWP* developed at the University of Oxford. Scientists there examined the climate impact of a constant stream of methane emissions rather than the effect of a given 1kg emission over the next century. Its authors found that a slow decrease in methane emissions of 10 per cent over 30 years caused no additional warming – as opposed to carbon dioxide, where emissions must stop completely and immediately to cause no additional warming.

The IPCC report clarified that metrics are just that – ways of measuring physics. It finds that achieving net-zero emission as measured through the traditional assessment of various gases over 100 years “typically leads to declining temperatures after net-zero greenhouse gas emissions are achieved if the basket includes short-lived gases, such as methane”. Meanwhile, using an alternative metric such as GWP* “corresponds approximately to reaching net-zero CO₂ emissions, and would thus not lead to declining temperatures after net-zero greenhouse gas emissions are achieved but to an approximate temperature stabilization”.

The IPCC adds: “Ultimately, it is a matter for policymakers to decide which emission metric is most applicable to their needs. This report does not recommend the use of any specific emission metric as the most appropriate metric depends on the policy goal and context.” In other words, we know what various gases do – the yardstick you use to measure your emissions doesn’t change the size of their climate impact.

“Strong reductions in other greenhouse gas emissions are needed. Amongst these, methane reductions.”

Valérie Masson-Delmotte, IPCC

Based on methane’s short-lived warming effect, which is confirmed in the IPCC report, Irish policy has been to seek a steady level of methane emissions (meaning a steady number of cattle) that would result in no additional warming. The objective has been to protect the continuing rise in dairy production, compensated by a reduction in the beef herd and additional measures elsewhere.

This was first formulated in the Department of Agriculture’s “Ag Climatise” plan last December, which listed a number of technical actions and stated: “This roadmap is based on stabilising methane emissions and a significant reduction in fertiliser related nitrous oxide emissions, leading to an absolute reduction in the agricultural greenhouse gas inventory by 2030. Any increase in biogenic methane emissions from continually increasing livestock numbers will put the achievement of this target in doubt.”

Ag Climatise stopped short of setting hard targets, but the government referred to previous IPCC publications to estimate a 24 to 47 per cent cut in methane emissions would be needed by 2050 to achieve no additional warming.

Last week, the new Food Vision 2030 national strategy filled the gaps. It was drafted by a committee of farmers, agribusiness leaders, civil servants and academics – and one representative of the NGO group Environmental Pillar until it left the process in February in protest at the document’s level of environmental ambition.

Food Vision 2030 formally adopts the 2050 bracket of a 24 to 47 per cent reduction in agricultural methane and adds an intermediary 10 per cent cut by 2030 “so that by 2050, the climate impact of methane is reduced to zero”. The strategy references the IPCC and “the approach being taken elsewhere” in setting these targets, which are directly lifted from New Zealand’s recent legislation. It also acknowledges that more detailed plans will be needed next year to implement the new carbon budgets in the beef and dairy sector and update Ag Climatise, which “was only a first step”.

Less than one week later, the IPCC report indicates the amount of updating required. 

“To limit global warming, strong, rapid and sustained reductions in CO₂ and other greenhouse gases are necessary,” Valérie Masson-Delmotte, co-chair of the working group that authored the report, said on Monday. “While CO₂ is the dominant greenhouse gas related to human influence on climate and reaching net-zero CO₂ is required to limit global warming, strong reductions in other greenhouse gas emissions are needed. Amongst these, methane reductions, together with strong air pollution controls, would benefit both the climate and improve air quality.”

The report explains the complex interactions between various pollutants behind this comment. Human activities release not only greenhouse gases, but also “aerosols” – to you and me, soot. These cause untold health and environmental damage, yet they also protect us from a portion of global warming by reflecting some of the sun’s radiation and interacting with clouds. 

Now the IPCC expects welcome changes such as reduced coal use to result in lower amounts of these aerosols in the atmosphere, which would, in turn, cause additional warming. “This warming is stable after 2040 in scenarios leading to lower global air pollution as long as methane emissions are also mitigated,” the report finds.  “Because of the short lifetime of both methane and aerosols, these climate effects partially counterbalance each other.”

There you have it. Reducing fossil fuel use, as is badly needed, means we also have to reduce methane emissions because it is the only way to avoid unwanted side effects in the short term.

By how much?

Among the “scenarios” mentioned for the rest of this century, only two are in line with the Paris Agreement’s commitment to keep global warming between 1.5°C and 2°C above pre-industrial temperatures and avoid global catastrophe. Both simulations assume a 75 per cent reduction in overall methane emissions between 2015 and 2100, with the greatest cuts taking place in the coming two to three decades.

The most optimistic, code-named SSP1-1.9, forecasts that the amount of methane released in the atmosphere will halve in the early 2040s. The next best scenario, SSP1-2.6, envisages this by the mid-2050s. 

If Irish agriculture was to play an equal part in this global methane trend, the most ambitious target considered in the Food Vision strategy of a 47 per cent cut by 2050 would become the bare minimum needed to remain within the targets of the Paris Agreement. 

This would also assume that any other Irish sources of the gas decrease their emissions in the same way, which puts into question another major Irish primary production project. If natural gas extraction is a major source of methane, as the IPCC reports, then it makes Providence Resources’ planned drilling of the Barryroe gas field off the Cork coast difficult to imagine as emissions of the gas become a short-term priority.

Further reading

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