Despite economic lockdowns, CO₂ and CH₄ concentrations surged in 2020

9 April 2021

Levels of the two most important anthropogenic greenhouse gases, carbon dioxide and methane, continued to rise in 2020, despite the economic slowdown caused by the coronavirus pandemic response, according to preliminary data by the US National Oceanic and Atmospheric Administration (NOAA).

The global surface average for carbon dioxide, calculated from measurements collected at NOAA’s remote sampling locations, was 412.5 ppm in 2020, rising by 2.6 ppm during the year. The global rate of increase 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 414.4 ppm during 2020.

NOAA scientists believe, however, that the economic slowdown prevented a record increase in CO₂ concentrations. The economic recession was estimated to have reduced carbon emissions by about 7% during 2020. Without the economic slowdown, the 2020 increase would have been the highest on record, according to Pieter Tans, senior scientist at NOAA’s Global Monitoring Laboratory. Since 2000, the global CO₂ average has grown by 43.5 ppm, 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 450 ppm. During that time sea level was about 24 m (78 ft) higher than today, the average temperature was 3.9°C (7°F) higher than in pre-industrial times, and studies indicate large forests occupied areas of the Arctic that are now tundra.

The ambient concentrations of methane also surged during 2020, according to NOAA. While CH₄ is far less abundant, it is 28 times more potent than CO₂ at trapping heat over a 100-year time frame. NOAA’s preliminary analysis showed the annual increase in atmospheric CH₄ for 2020 was 14.7 ppb, which is the largest annual increase recorded since systematic measurements began in 1983. The global average burden of methane for December 2020, the last month for which data has been analyzed, was 1892.3 ppb. That would represent an increase of about 119 ppb, or 6%, since 2000.

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. Determining which specific sources are responsible for variations in methane annual increase is difficult, NOAA said. Preliminary analysis of carbon isotopic composition of CH₄ 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 like oil and gas production and use.

The NOAA Global Monitoring Laboratory makes highly accurate measurements of the three major greenhouse gases, CO₂, CH₄, and N₂O, from four baseline observatories in Hawaii, Alaska, American Samoa, and the South Pole, and from samples collected by volunteers at more than 50 other 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.

Source: NOAA