Carbon dioxide now at highest level in 3.6 million years

May 4, 2021
Despite pandemic shutdowns, atmospheric carbon dioxide and methane levels surged last year. Photo: marcinjozwiak from Pixabay

Caption: CO2 concentration at the Mauna Loa Observatory reached a daily record of 421.21 parts per million on April 3, 2021. That is 50% higher than the pre-industrial level.

Levels of the two most important anthropogenic greenhouse gases, carbon dioxide and methane, continued their unrelenting rise last year, despite the economic slowdown caused by the COVID-19 pandemic response, the United States National Oceanic and Atmospheric Administration (NOAA) announced on April 7.

The global surface average for carbon dioxide (CO2), calculated from measurements collected at NOAA’s remote sampling locations, was 412.5 parts per million (ppm) in 2020, rising by 2.6ppm during the year.

The global rate of rise was the fifth-highest in NOAA’s 63-year record, following 1987, 1998, 2015 and 2016. The annual mean at NOAA’s Mauna Loa Observatory in Hawaii was 414.4ppm during 2020.

Economic slowdown prevented a record increase in CO2

The economic recession was estimated to have lowered carbon emissions by about 7% during 2020. Without the economic slowdown, last year’s rise would have been the highest on record, according to Pieter Tans, senior scientist at NOAA’s Global Monitoring Laboratory (GML). Since 2000, the global CO2 average has grown by 43.5ppm, an increase of 12%.

The atmospheric burden of CO2 is now comparable to where it was during the Mid-Pliocene Warm Period around 3.6 million years ago, when concentrations of carbon dioxide ranged from about 380 to 450ppm. During that time, sea level was about 24 metres higher than today, the average temperature was 13.9℃ higher than in pre-industrial times, and studies indicate large forests occupied areas of the Arctic that are now tundra.

“Human activity is driving climate change,” said Colm Sweeney, assistant deputy director of the GML. “If we want to mitigate the worst impacts, it’s going to take a deliberate focus on reducing fossil fuel emissions to near zero — and even then we’ll need to look for ways to further remove greenhouse gases from the atmosphere.”

The GML makes highly accurate measurements of the three major greenhouse gases — carbon dioxide, methane and nitrous oxide — from four baseline observatories in Hawaii, Alaska, American Samoa and the South Pole, and from samples collected by volunteers at more than 50 other cooperative sampling sites around the world.

These measurements are incorporated into the Global Greenhouse Gas Reference Network and are a vital reference widely used by international climate researchers.

Caption: Atmospheric Methane

Methane levels also surged

Analysis of samples from last year also 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.

NOAA’s preliminary analysis showed the annual rise in atmospheric methane for 2020 was 14.7 parts per billion (ppb), which is the largest annual rise recorded since systematic measurements began in 1983. The global average burden of methane for December 2020 -- the last month for which data has been analysed — was 1892.3ppb. That would represent a rise of about 119ppb, or 6%, since 2000.

In early April, GML typically releases a preliminary estimate of the global annual atmospheric increase for key greenhouse gases from January 1st in one year to January 1st in the next year. This preliminary estimate is based on measurements from weekly air samples collected at about 40 sites around the world.

While GML’s preliminary estimates are typically a little higher than the final calculation, which incorporates additional measurements, the 2020 rise is likely to remain one of the largest in the entire record.

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 by-product of livestock farming. Determining which specific sources are responsible for the variations in annual methane rise is difficult.

Preliminary analysis of carbon isotopic composition of methane in the NOAA air samples done by the Institute of Arctic and Alpine Research at the University of Colorado, indicates that it is likely that a primary driver of the increased methane burden comes from biological sources of methane such as wetlands or livestock, rather than thermogenic sources such as oil and gas production and use.

“Although increased fossil emissions may not be fully responsible for the recent growth in methane levels, reducing fossil methane emissions are an important step toward mitigating climate change,” said GML research chemist Ed Dlugokencky.

[Abridged from Climate and Capitalism.]

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