On October 28, the UN published an alarming report on the continued rise in greenhouse gas (GHG) concentrations in the atmosphere. While COP29 will soon be held in Baku, the World Meteorological Organization (WMO) warns that this perpetual increase in emissions makes it even more difficult to limit global warming to +2°C, the objective set by the Paris Agreement. In 2023, levels of CO2, methane (CH4) and nitrous oxide (N2O) have reached records, foreshadowing a certain rise in temperatures for years to come. “Another year, another record,” lamented Celeste Saulo, Secretary General of WMO, urging decision-makers to act.
This annual report on greenhouse gases, published by the UN just before the climate conference, highlights in particular the acceleration of the accumulation of CO2 in the atmosphere, which has increased by more than 10% in twenty years . The WMO explains that these figures are not simple abstract data: each increase, even small, in gas concentrations has real and tangible consequences for the planet and its inhabitants.
Commitments still insufficient to contain global warming
At COP21, countries committed to limiting warming to 2°C compared to pre-industrial levels, or even 1.5°C if possible. However, another UN Climate report, published the same day, indicates that current commitments will only allow a 2.6% reduction in GHG emissions by 2030 compared to 2019, when it would be necessary aim for a reduction of 43% to hope to limit the increase to 1.5°C. The persistence of emissions leads to a continued accumulation of GHGs in the atmosphere, which, according to the WMO, guarantees an increase in temperatures over the coming decades.
The 2023 readings show concentrations of CO2 reaching 420 parts per million (ppm), methane at 1,934 parts per billion (ppb), and nitrous oxide at 336 ppb. These values exceed the levels of 1750 by 151%, 265%, and 125% respectively. According to Celeste Saulo, these figures clearly show that the increase in concentrations has very real effects, with each additional fraction of a degree directly affecting ecosystems and living conditions.
Towards a possible vicious climatic circle
CO2, responsible for 64% of warming, increased by 2.3 ppm in 2023, marking the twelfth consecutive year in which this increase exceeded 2 ppm, due to high emissions from fossil fuels during the 2010s and 2020s. This level of CO2 concentration is reminiscent of conditions 3 to 5 million years ago, when the global temperature was 2 to 3°C higher and the level of seas much higher.
Although around half of CO2 emissions are absorbed by oceans and terrestrial ecosystems, the WMO warns of a potential “vicious cycle” where these ecosystems, destabilized by climate change, could themselves become sources of emissions. Forest fires, for example, release significant amounts of carbon, while warmer oceans risk reducing their capacity to absorb CO2. According to Ko Barret, WMO Deputy Secretary-General, this could lead to an acceleration of warming, creating a cycle that worsens the effects of climate change.
