In yet another ominous warning for the future of our planet, atmospheric levels of the three main greenhouse gases - carbon dioxide, methane and nitrous oxide all reached new record highs in 2021, according to a new report from the World Meteorological Organization (WMO).
WMO’s Greenhouse Gas Bulletin reported the biggest year-on-year jump in methane concentrations in both 2020 and 2021 since systematic measurements began nearly 40 years ago. The reason for this exceptional increase is not clear, but seems to be a result of both biological and human-induced processes.
Carbon dioxide (CO2)
Atmospheric carbon dioxide reached 149% of the pre-industrial level in 2021, primarily because of emissions from the combustion of fossil fuels and cement production. Global emissions have rebounded since the COVID-related lockdowns in 2020. Of the total emissions from human activities during the 2011–2020 period, about 48% accumulated in the atmosphere, 26% in the ocean and 29% on land.
There is concern that the ability of land ecosystems and oceans to act as “sinks” may become less effective in future, thus reducing their ability to absorb carbon dioxide and act as a buffer against larger temperature increase. In some parts of the world the transition of the land sink into CO2 source is already happening.
Atmospheric methane is the second largest contributor to climate change and consists of a diverse mix of overlapping sources and sinks, so it is difficult to quantify emissions by source type.
Since 2007, globally-averaged atmospheric methane concentration has been increasing at an accelerating rate. The annual increases in 2020 and 2021 (15 and 18 ppb respectively) are the largest since the systematic record began in 1983.
Causes are still being investigated by the global greenhouse gas science community. Analysis indicates that the largest contribution to the renewed increase in methane since 2007 comes from biogenic sources, such as wetlands or rice paddies. It is not yet possible to say if the extreme increases in 2020 and 2021 represent a climate feedback – if it gets warmer, the organic material decomposes faster. If it decomposes in the water (without oxygen) this leads to methane emissions. Thus, if tropical wetlands become wetter and warmer, more emissions are possible.
The dramatic increase might also be because of natural interannual variability. The years 2020 and 2021 saw La Niña events which are associated with increased precipitation in the tropics.
Nitrous oxide (N2O)
Nitrous oxide is the third most important greenhouse gas. It is emitted into the atmosphere from both natural sources (approximately 57%) and anthropogenic sources (approximately 43%), including oceans, soils, biomass burning, fertilizer use, and various industrial processes. The increase from 2020 to 2021 was slightly higher than that observed from 2019 to 2020 and higher than the average annual growth rate over the past 10 years