According to WMO’s Greenhouse Gas Bulletin, released in 2021, atmospheric levels of the three main greenhouse gases - carbon dioxide, methane and nitrous oxide all reached new record highs.
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. Roughly half of the CO2 emitted by human activity remains in the atmosphere, while the other half is taken up by land and ocean, which act as sinks - systems able to absorb GHGs. The balance between sources and sinks changes yearly due to natural variability.
With an increase in future GHG emissions, land ecosystems and oceans become less effective at absorbing CO2 and acting as a buffer against temperature increases, which could lead to more warming in the Earth's atmosphere.
Methane (CH4) accounts for about 16% of the warming effect of long-lived GHGs and stays in the atmosphere for about a decade. 40% of methane in the atmosphere comes from natural sources, such as wetlands, while human activities, for example, rice agriculture and biomass burning, account for the remaining 60%.
Nitrous Oxide (N2O) is a potent greenhouse gas and ozone-depleting chemical. It accounts for about 7% of the warming caused by long-lived GHGs. Human-induced sources, such as fertilizer use and biomass burning, account for approximately 40% of its GHG presence.