THE role of methane in global warming is distorted because methane is a short-lived gas that does not leave a warming legacy, according to an Oxford University physicist and IPCC contributing scientist.
Dr Myles Allen said a key factor in this misunderstanding was that the formula used globally to assess the warming impact of different greenhouse gases was getting it wrong.
“The problem is we have widespread misunderstanding and confusion about how methane influences global climate,” he said during a recent presentation to livestock producers, government representatives and media hosted by Cattle Australia in Canberra.
Dr Allen said the most widely-used system for assessing the warming impact of different greenhouse gas emissions, known as GWP100 (Global Warming Potential 100), pretended that methane was a kind of carbon dioxide (CO2).
“It isn’t,” he said.
“If we were to refocus climate policy on warming outcomes rather than emissions inputs, we might actually find it much easier to engage farmers on climate policy.”
Dr Allen said it mattered that the most widely-used metric was not providing an accurate picture, “because we need to know the impact of our actions on global temperature”.
The scientist behind GWP, Dr Allen maintains he is not for the livestock sector or against it, stressing that he was simply for the science and what the numbers say and where they lead.
“Einstein told us, make everything as simple as possible, but not simpler,” he said.
GWP (Global Warming Potential Star), he said, is a more accurate measure than GWP100 of the warming effect of short-term gases like methane.
Dr Allen said the problem with GWP100 was highlighted in a recent IPCC assessment report that “no body is arguing with”.
The key point was the quote: “Expressing methane emissions as CO2 equivalent using 100-year Global Warming Potential (GWP100) overstates the effect of constant methane emissions on global temperature by a factor of three to four, while understating the effect of any new methane emission source by a factor of four to five, over the 20 years following the introduction of the new source”.
“So these are big errors,” Dr Allen said. “This is a factor of 300-400 percent.”
This was not academic quibbling over 20 per cent here or there.
“These are big differences in the way the gases behave.”
Reading past the comma in the quote had led some to suggest GWP effectively allows the cattle industry to relax, take its foot off the pedal and not worry about methane. Dr Allen warned against that conclusion, urging the livestock sector to “read past the comma”.
That was the part that says GWP100 “understates” the warming effect of any new source of methane emissions over a 20-year-period (such as a cattle herd increasing in size over that time) by a factor of four to five, or 400-500 percent.
“I think there has been a bit of a tendency for the farming community to stop reading at the comma,” Dr Allen said.
“Obviously, the first half of the sentence seems quite positive, good news for you, but you have got to look at the second half as well.”
Boost for cattle on methane emissions
Stable herds with decreasing emissions negated a warming effect. But a key overall message for the livestock sector was this: in a stable herd with emissions gently decreasing over time at a rate of 0.3 percent per year over 20 years -which could be achievable through genetic selection, animal health improvements and emissions-inhibiting feed supplements – the warming effect of emissions would be negated.
And if a herd’s emissions could be reduced at a greater rate than 0.3pc per year, it had the same impact on global temperature as actively removing carbon dioxide from the atmosphere, pulling global temperatures down.
“So this is where we have an opportunity,” Dr Allen said.
Short-lived methane emissions behaved “totally differently” in the atmosphere than long-lived CO2 emissions, which remain in the climate system for thousands to tens of thousands of years, accumulating ever faster and leading to accelerated warming.
Conversely, Dr Allen said, methane has a short lifetime in the climate system, about 10 years.
“When methane emissions are rising with the addition of new sources, they will cause global warming. But if you are reducing methane emissions over time, the warming they cause is reduced,” he said.
“Methane oxidises in the atmosphere, and as the amount of methane in the atmosphere falls, so does the warming it causes.”
When emissions are reduced over time, the industry can reverse its warming impact, he said, something that did not apply to CO2 emissions from fossil fuels.
“If we can reduce global methane emissions from the livestock sector, we’re doing the same favour to the world as planting trees to taking CO2 out of the atmosphere – we’re pulling down global temperatures,” he said.
Dr Allen said warming effects of different gases should be accounted for independently, particularly methane and CO2, which GWP enables.
The world has agreed to hold the rise in average global temperature to well below 2 degrees, but “not a single country actually reports the warming impact of their emissions”.
Despite the demonstrated limitations of GWP100, the United Nations Framework for Convention on Climate Change annual conference recently agreed to adopt that metric globally.
This had also caused a misconception that only GWP100-based metrics could be used.
However, Dr Allen said UN rules still explicitly allowed each country to use metrics other than GWP100.
The aim was to stop global warming from individual countries, but nobody was reporting the impact of their emissions on global temperature.
“It is staggering if you stop and think about it,” he said.”
Farming organisations in NZ and the UK call for adoption of GWP*”.
An umbrella group of developed countries outside the EU, which includes Australia, New Zealand and the UK, had recently formed.
Dr Allen said for the sake of transparency, those groups should state the warming impact of their emissions to the UNFCCC, in addition to their national contributions.
“The warming impact is easy to calculate – the formula involves two multiplications and a subtraction, the old formula involved one multiplication – don’t let anybody tell you it is too complicated,” he said.
He also pointed out that farming unions in the UK and NZ have also been calling for their nations to support the adoption of reporting as GWP*.
Dr Allen said he was not aware of any Australian farming union joining this conversation.
“I think you should, because it matters; we need to know the impact of our actions on global temperature,” he said.
“It is something that Australia could really make a positive impact on international negotiations by stepping forward to improve transparency by reporting warming impact as well as the conventional carbon footprint.”
Dr Allen said separating methane from carbon dioxide in setting climate targets was “the one thing absolutely everybody agreed on”, as was shown in a paper involving 35 authors who had published on greenhouse gas accounting metrics in the years since the Paris Agreement was signed.
“If you want to know the impact of your targets and policies on global temperature, you have got to keep these things separate, there is no point pretending they’re equivalent.
So, everybody agreed on that, but it doesn’t seem to so far have made any difference,” he said.
“All of the scientists are saying the same thing – separate these things out. The likes of the UK Government or European Commission are saying well, no, ‘We like to mix them up’. I am not quite sure what more we can say as a scientific community. Now it is kind of going to be over to you to digest all this and talk to your government about what it would take to change things.”