Concentrations of methane, a key driver of climate change, have risen faster than ever before over the last five years, the Global Carbon Project’s Global Methane Budget shows.
The budget, published on Tuesday in the journal Earth System Science Data, is produced by international scientific agencies, including the CSIRO.
After carbon dioxide, methane was the most important greenhouse gas contributing to human-induced climate change, CSIRO Chief Research Scientist Pep Canadell said.
While it remains in the atmosphere for a much shorter timeframe, it has a higher global warming potential than carbon dioxide (86 times larger over 20 years), because methane holds more heat in the atmosphere.
Dr Canadell said the budget showed that methane emissions from human activities had increased by 20 per cent in the past two decades.
“Methane concentrations have risen faster than ever over the last five years,” he said.
"As a result of increased anthropogenic methane emissions, concentration in the atmosphere is now 2.6 times higher than its pre-industrial (1750) level."
He warned that methane concentrations are following the trends of the Intergovernmental Panel on Climate Change’s “most pessimistic” illustrative future for greenhouse gas emission trajectories.
"These findings would indicate global mean temperatures above 3C by the end of this century, which exceeds the target of limiting global warming by 1.5C,” he said.
"If the trend of anthropogenic methane emissions continues to increase, this could jeopardise the success of the Global Methane Pledge (international commitment to reduce by 30 per cent methane emissions by 2030)."
CSIRO was working on a range of research and innovation to support sustainability goals to reduce methane emissions, according to CSIRO’s Towards Net Zero Lead, Dr Michael Battaglia.
“Mitigation efforts include developing FutureFeed, with partners Meat & Livestock Australia and James Cook University, an Asparagopsis seaweed-based feed additive to significantly reduce enteric methane emissions in livestock. This is one of an array of feed supplements in a suite of technologies to address ruminant methane,” Dr Battaglia said.
The scientists who produced the budget say that understanding and quantifying the global methane budget is important for assessing realistic pathways to mitigate climate change.
The budget, which is updated every two years, reveals and analyses methane trends for the past two decades.
It covers 17 natural and anthropogenic (human-induced) sources and four sinks.
Agriculture contributes 40 per cent of global anthropogenic emissions. This is followed by the fossil fuel sector (34 per cent). Solid waste and wastewater contribute 19 per cent, while biomass and biofuel burning represent 7 per cent.
The top five country emitters by volume of anthropogenic methane in 2020 were China (16 per cent), India (9 per cent), USA (7 per cent), Brazil (6 per cent), and Russia (5 per cent).
Dr Canadell said there had been a drop in methane emissions in Australia over the last two decades.
“The slight emission decrease in Australia is from agriculture," he said.
Human activities are responsible for at least two-thirds of global methane emissions. Methane emissions from human activities have added about 0.5C to current global warming.
Dr Canadell said that for net-zero emission pathways consistent with the Paris Agreement, which is stabilising temperatures below a 2C increase from pre-industrial levels, human-induced methane emissions needed to decline by 45 per cent, relative to 2019 levels, by 2050.
"Meeting the Global Methane Pledge would reduce methane emissions to a level consistent with 1.5C pathways while delivering significant benefits for human and ecosystem health, food security and our economies,” he said.
