• The concentration of greenhouse gases in the atmosphere reached a record high in 2022, the World Meteorological Organisation (WMO) said.

• Global averaged concentrations of carbon dioxide (CO2), the most important greenhouse gas, in 2022 were a full 50 per cent above the pre-industrial era for the first time. They continued to grow in 2023.

• Methane concentrations also grew, and levels of nitrous oxide (N2O), the third main gas, saw the highest year-on-year increase on record from 2021 to 2022, according to WMO’s Greenhouse Gas Bulletin.

What are greenhouse gases?

• The Earth has a natural greenhouse effect due to trace amounts of water vapour (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the atmosphere. These gases let the solar radiation reach the Earth’s surface, but they absorb infrared radiation emitted by the Earth and thereby lead to the heating of the surface of the planet. 

• In simpler terms, gases that trap heat in the atmosphere are called greenhouse gases.

• The main greenhouse gases whose concentrations are rising are carbon dioxide, methane, nitrous oxide, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and ozone in the lower atmosphere.

• The current level of greenhouse gas concentrations puts us on the pathway of an increase in temperatures well above the Paris Agreement targets by the end of this century. This will be accompanied by more extreme weather, including intense heat and rainfall, ice melt, sea-level rise and ocean heat and acidification. 

Carbon dioxide

• Carbon dioxide is the single most important greenhouse gas in the atmosphere, accounting for approximately 64 per cent of the warming effect on the climate, mainly because of fossil fuel combustion and cement production.

• Just under half of CO2 emissions remain in the atmosphere. Just over one quarter are absorbed by the ocean and just under 30 per cent by land ecosystems like forests — although there is considerable year-to-year variability in this. As long as emissions continue, CO2 will continue accumulating in the atmosphere leading to global temperature rise. 

• Given the long life of CO2, the temperature level already observed will persist for several decades even if emissions are rapidly reduced to net zero.

• The 2.2 parts per million (ppm) increase in the annual average from 2021 to 2022 was slightly smaller than 2020 to 2021 and for the past decade (2.46 ppm yr). 

• The most likely reason is increased absorption of atmospheric CO2 by terrestrial ecosystems and the ocean after several years with a La Niña event. The development of an El Niño event in 2023 may therefore have consequences for greenhouse gas concentrations.

• 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.

Methane

• Methane is a powerful greenhouse gas which remains in the atmosphere for about a decade. Methane accounts for about 16 per cent of the warming effect of long-lived greenhouse gases.

• Approximately 40 per cent of methane is emitted into the atmosphere by natural sources (for example, wetlands and termites), and about 60 per cent comes from anthropogenic sources (for example, ruminants, rice agriculture, fossil fuel exploitation, landfills and biomass burning).

• The increase from 2021 to 2022 was slightly lower than the record rate observed from 2020 to 2021 but considerably higher than the average annual growth rate over the last decade.

Nitrous Oxide

• Nitrous Oxide (N2O) is both a powerful greenhouse gas and ozone depleting chemical. It accounts for about 7 per cent of the radiative forcing by long-lived greenhouse gases.

• N2O is emitted into the atmosphere from both natural sources (approximately 60 per cent) and anthropogenic sources (approximately 40 per cent), including oceans, soils, biomass burning, fertilizer use, and various industrial processes.

• For N2O, the increase from 2021 to 2022 was higher than that observed any time before in our modern time record.

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