The concentration of methane in the atmosphere last year reached its highest level since systematic measurements began almost 40 years ago, according to the World Meteorological Organisation (WMO) in Geneva.
The cause for this extraordinary increase is not clear but it seems to be due to both biological and human-induced processes, the organisation reported.
In addition to methane, two other major greenhouse gases, carbon dioxide (CO2) and nitrous oxide, were also at their highest levels ever, according to the WMO’s annual Greenhouse Gas Bulletin.
Methane (CH4) is the second largest contributor to climate change after carbon dioxide. It is produced when organic matter decomposes in the absence of air and is 25 times more harmful to the climate than CO2. However, it remains in the atmosphere for a much shorter time.
Methane takes more than ten years to leave the atmosphere, whereas a significant proportion of CO2 is still around even after centuries. CO2 contributes about two-thirds to the greenhouse effect, methane over 16% and nitrous oxide about 6.5%.
Greenhouse gases as a whole have led to average global warming of 1.1 degrees since the late 19th century. According to WMO estimates, global average methane concentration increased by 18 ppb to 1,908 ppb (particles of methane per billion particles) in 2021, which was 262% of pre-industrialisation levels.
The year before, it had increased by 15 ppb, which was also significantly higher than the long-term average.
Much of the increase is likely to have come from swamps and rice fields, according to the WMO. It is still unclear whether this is a consequence of climate change, for example, as marshes become wetter and warmer. The warmer the temperature, the faster organic matter decomposes, and decomposition in water without oxygen supplies leads to higher methane emissions.
However, the WMO says. “the dramatic increase could also be due to natural annual variability.”
For carbon dioxide, the increase in concentration from 2020 to 2021 was higher than the average of the previous 10 years, the study said. Concentrations rose by 2.5 ppm to 415.7 ppm (particles of CO2 per million particles) in 2021. This corresponds to 149% of pre-industrialisation levels around 1750.
CO2 is produced, for example, by the burning of coal, oil and gas, the production of cement and other industrial processes, and the destruction of forests.
Depending on the measuring stations and calculation methods, WMO values differ slightly from data coming, for example, from the US climate authority NOAA. The WMO calculates an average value based on measurements from different stations.
