The abundance of heat-trapping greenhouse gases in the atmosphere once again reached a new record in 2021, with the annual rate of increase above the 2011-2020 average. That trend has continued in 2021, according to the World Meteorological Organization (WMO) Greenhouse Gas Bulletin.
Concentration of carbon dioxide (CO2), the most important greenhouse gas, reached 413.2 parts per million in 2020 and is 149% of the pre-industrial level. Methane (CH4) is 262% and nitrous oxide (N2O) is 123% of the levels in 1750 when human activities started disrupting Earth’s natural equilibrium.
Roughly half of the CO2 emitted by human activities today remains in the atmosphere. The other half is taken up by oceans and land ecosystems. The Bulletin flagged 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…Such changes are already happening, for example, transition of the part of Amazonia from a carbon sink to a carbon source.
The Bulletin shows that from 1990 to 2020, radiative forcing – the warming effect on our climate – by long-lived greenhouse gases increased by 47%, with CO2 accounting for about 80% of this increase…The amount of CO2 in the atmosphere breached the milestone of 400 parts per million in 2015. And just five years later, it exceeded 413 ppm.
“Carbon dioxide remains in the atmosphere for centuries and in the ocean for even longer. The last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago, when the temperature was 2-3°C warmer and sea level was 10-20 meters higher than now. But there weren’t 7.8 billion people then,” said Prof. Taalas.
Excerpt from Greenhouse Gas Bulletin: Another Year Another Record, WMO, Oct. 25, 2021