Methane levels and the role of science in mitigation
Rising methane levels in our atmosphere have been making headlines around the globe.
The annual United Nations Climate Change Conference, COP27, is underway in Egypt, where the Global Methane Pledge is under the spotlight.
In October, Australia joined the pledge to cut methane emissions by 30 per cent by 2030.
Ahead of COP27, the World Meteorological Organization (WMO) released its Greenhouse Gas Bulletin looking at levels of carbon dioxide, methane and nitrous oxide in the atmosphere.
The Bulletin reported the biggest year-on-year increase in methane concentrations in 2021, since systematic atmospheric measurements began nearly four decades ago.
But the reason for the accelerated increase is unclear.
So what is methane and where does it come from?
A powerful greenhouse gas
Methane, or CH4, is an odourless gas composed of one carbon atom and four hydrogen atoms.
The lead of CSIRO’s Greenhouse Gas Observations team, Dr Zoë Loh, says methane has a relatively short atmospheric lifetime.
“While carbon dioxide, or CO2, stays in the atmosphere for hundreds of years, methane has an atmospheric lifetime of less than a decade,” says Dr Loh.
“However, each molecule of methane is much more effective at trapping heat in the atmosphere than a molecule of CO2.”
Over a 20-year-period, methane’s global warming potential is 83 times higher than carbon dioxide.
“Because methane is so good at trapping heat, reducing emissions of the gas over the coming decades are critical to reaching net zero emissions and halting global warming,” Dr Loh says.
“But the good news here is that because methane has a short atmospheric lifetime, effective action at reducing emissions will provide a near-term brake on climate forcing, while we wind down CO2 emissions.”
Researcher at the University of New South Wales School of Biological, Earth and Environmental Sciences, Lexie Lu, says many sources release methane into the atmosphere.
“For instance, methane is naturally produced from wetlands and freshwater by microbes in anaerobic conditions,” Ms Lu says.
About 40 per cent of methane is emitted into the atmosphere from these natural sources, which also include rivers, termites and natural geological sources, such as gas-oil seeps.
“Since the industrial revolution, human activities have contributed a significant amount of methane emissions via numerous anthropogenic sources including agriculture, waste and fossil fuels,” Ms Lu says.
These human sources also include biomass burning, wastewater treatment, the decomposition of organic matter in landfills and emissions from agriculture.
In Australia, the contribution of methane emissions from ruminant livestock is nearly 10 per cent of total greenhouse gas emissions.
That’s why scientists at CSIRO are exploring methane-reducing initiatives, like FutureFeed.
CSIRO scientists collaborated with Meat & Livestock Australia and James Cook University to develop a cost-effective seaweed feed ingredient native to Australia that significantly reduces methane emissions and has potential to increase livestock productivity.
Atmospheric Composition and Chemistry research group leader and Kennaook/Cape Grim Lead Scientist at CSIRO, Paul Krummel, says the amount of methane in the atmosphere has been rising year-on-year for the past 200 years, except for a short period between 2000 and 2007.
“Since 2007, atmospheric methane has been increasing again at an accelerating rate,” he says.
The Kennaook/Cape Grim Baseline Air Pollution Station near Tasmania’s isolated north-west tip records the greenhouse gas data from one of the cleanest air sources in the world.
The station is the joint responsibility of the Bureau of Meteorology and CSIRO.
“In 2021, the average amount of methane in clean air off the Southern Ocean was 17 parts per billion (ppb) higher than it had been in 2020,” Mr Krummel said.
“That is the highest year-on-year increase measured since the mid-1980s when systematic atmospheric measurements commenced.”
The measurement is in line with global trends.
The World Meteorological Organisation’s (WMO) Greenhouse Gas Bulletin, released in October 2022, reported that the globally-averaged atmospheric methane concentration increases in 2020 and 2021 were the largest since records began, at 15 and 18 ppb respectively.
This increase is higher than the average annual increase over the past decade.
Overall, the increase in atmospheric methane has reached 262 per cent of the pre-industrial level.
WMO Secretary-General, Professor Petteri Taalas, says the record acceleration in methane levels shows we’re heading in the wrong direction.
“The WMO’s Greenhouse Gas Bulletin has underlined, once again, the enormous challenge – and the vital necessity – of urgent action to cut greenhouse gas emissions and prevent global temperatures rising even further in the future.”
What’s causing the rise in methane levels?
The scientific community is continuing to investigate the causes of the recent spike in atmospheric methane levels.
According to the WMO, analysis indicates that increased emissions are coming from sources such as rice farms and tropical wetlands, especially in Africa.
Dr Loh says it remains possible that the recent increases are due to natural inter-annual variability, with La Niña events in 2020 and 2021 associated with increased rainfall in the tropics.
But she says if we’re seeing the beginning of a significant, permanent increase in methane emissions from a natural source, this would indicate the start of a ‘positive feedback loop’.
“This is where the climate changes that have already occurred due to human emissions are enough to trigger higher natural emissions of greenhouse gases,” she says.
“In this instance, the worry is that warmer, damper conditions that now prevail in the tropics might have tipped those microbial sources into overdrive production of methane.
“This would mean that they have now become permanently bigger sources of methane, thereby driving additional warming.”
The urban methane emissions mitigation project
While cities make up 3 per cent of the world’s land surface, they’re responsible for about 20 per cent of man-made methane emissions.
That’s why CSIRO is building an urban methane emissions mitigation project, based in Melbourne, which has Australia’s highest natural gas usage.
Leakage from natural gas infrastructure has been found to be a significant – and remediable – source of methane in many cities worldwide.
One of the measurement methods is to record the amount of methane in the atmosphere in mobile surveys, where a portable analyser is used with an inlet through a car window as it drives around Melbourne.
The preliminary work on the project shows methane is being emitted from landfill, wastewater treatment and gas leaks.
“One gas leak we found on a suburban street clocked in at an astounding 147 parts per million – around 80 times higher than the background value,” Dr Loh says.
“That leak was reported to the gas company. It was fixed, and we verified that in our next survey, which is a good result.”
“We have also seen some evidence that methane emissions from wood burning for heating might be a more significant source of methane in Melbourne during the cooler months than expected.”
You can follow the latest greenhouse gas data updated monthly from Kennaook/Cape Grim here.