Levels of the two most important greenhouse gases in the atmosphere – carbon dioxide (CO2) and methane – continued to surge last year, despite Covid-19 lockdowns, according to the National Oceanic and Atmospheric Administration (NOAA).
CO2 levels are now higher than at any time in the past 3.6-million years when concentrations ranged from about 380 to 450 parts per million (ppm), it said.
‘Human activity is driving climate change’
The global surface average for CO2, calculated from measurements collected at NOAA’s remote sampling locations, was 412.5ppm last year, rising by 2.6ppm during the year.
Professor Bob Scholes, a professor of systems ecology at the global change institute at the University of the Witwatersrand, told the Mail & Guardian that the rising global methane levels are predominantly, although not entirely, from biogenic sources such as wetlands and ruminants (cattle and sheep).
The economic recession was estimated to have reduced carbon emissions by about 7% during 2020. Without this, the 2020 increase would have been the highest on record, NOAA global monitoring laboratory senior scientist Pieter Tans said in a statement .
Since 2000, the global CO2 average has grown by 43.5ppm, an increase of 12%, according to NOAA’s data.
“Human activity is driving climate change,” laboratory assistant deputy director Colm Sweeney said in the statement. “If we want to mitigate the worst impacts, it’s going to take a deliberate focus on reducing fossil fuels emissions to near zero – and even then we’ll need to look for ways to further remove greenhouse gasses from the atmosphere.”
The methane mystery
NOAA said analysis of samples from last year showed a significant jump in the atmospheric burden of methane, which is far less abundant but 28 times more potent than CO2 at trapping heat over a 100-year time frame.
The preliminary analysis showed the annual increase in atmospheric methane for 2020 was 14.7 parts per billion (ppb), which is the largest annual increase recorded since systematic measurements began in 1983.
Methane in the atmosphere is generated by many different sources, such as fossil fuel development and use, decay of organic matter in wetlands and as a byproduct of livestock farming.
Scholes said it was somewhat puzzling that wetlands and ruminants were driving methane emissions up. “This is a bit of a mystery, because worldwide, wetlands are mostly being destroyed rather than created (or are being replaced by agricultural wetlands like paddy rice fields),” he said.
“One thought is that the steady increase may reveal the effects of permafrost melting in the Arctic as a result of climate change, creating methane emitting bogs.”
Scholes said new methane-detecting satellites may shine some light on the location of the sources. “Last year they noted that there are some previously unacknowledged large sources in Africa, particularly the Nile river swamp (the sudd) in Sudan. But finding those does not account for the global rise, since they have always been there.”
Complexities of livestock contributions
He said ruminants (cattle and sheep) are an important source and the global herd is increasing, but that story is also complicated.
“The simple equation that every hamburger you eat adds methane emissions to the atmosphere is very dependent on the particulars of how the meat was produced.
“Meat or milk produced under intensive operations (feedlots) is increasing in absolute and relative terms, but the methane emissions per kilogram of product is generally less than for free-range production and is declining in many instances – but it all depends on how the wastes are handled, which in South Africa, means rather badly.”
However, Scholes said, the cattle and sheep biomass in South Africa is almost exactly the same as the wild ruminant biomass that was originally here in pre-industrial times “so that can’t account for the rise either”.
Scholes said the rush out of coal is being compensated by a rush into natural gas, including in South Africa.
“Natural gas is methane, and much more powerful as a greenhouse gas than carbon dioxide. So if you leak just a tiny amount (2%) of the gas in the exploration, extraction, transport, storage and use chain … gas is not a less climate damaging option than coal. It turns out that a 2% leak is about the industry norm, and contributes to the observed global methane rise.”
NOAA said it is likely that a primary driver of the increased methane burden comes from wetlands or livestock rather than oil and gas production and use, but reducing fossil methane emissions is an important step toward mitigating climate change.