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La Niña slows atmospheric CO₂ rise: but not for long

Carbon dioxide will continue to accumulate in the atmosphere in 2023 due to ongoing emissions.

However, the Met Office is forecasting slower-than-usual buildup this year due to a temporary increase in natural carbon sinks — processes that absorb more carbon dioxide.

This effect will not be permanent and will need to be replaced by a rapid reduction in emissions if global warming is to be limited to 1.5°C.

To achieve this goal, the accumulation of CO₂ must become slower and eventually stop in about a decade. An accidental temporary cooling of the planet – as a result of the La Niña in the tropical Pacific – is now slowing CO₂ accumulation, prompting rainforests and other vegetation to absorb more carbon dioxide than usual for the third year in a row.

So while atmospheric CO₂ levels continue to rise due to emissions from fossil fuels and deforestation, the increase is smaller than it would be without additional carbon sequestration by the remaining forests.

To follow the 1.5°C scenario, growth must continue to decline year on year. This would only be possible through rapid and deep cuts in global emissions.

Annual change in atmospheric CO₂ concentration: The black line shows the observed change in atmospheric CO₂ concentration over the years, and the green line shows a calculation of what the annual change would be if it were only affected by emissions and the effects of El Niño and La Niña on there were no natural carbon sinks. The red star shows the projected growth from 2022 to 2023, taking into account the influence of the recent La Niña; the green star shows what the emissions-only forecast would be without the influence of La Niña. The gray bar shows a CO₂ growth scenario in which emissions decline fast enough to limit global warming to 1.5°C compared to pre-industrial times. Graphics: Meteorological Bureau. Observed CO₂ Data Source: Scripps Institution of Oceanography.

Professor Richard Betts, MBE, who leads the CO₂ forecast team, said: “While our forecast again points to slower accumulation this year, this is not because humanity emits less carbon. Instead, we get a free helping hand from nature – but only for now. Once La Niña weather stops, more of our emissions will remain in the atmosphere. We cannot rely on nature to do our work for us.”

The Met Office predicts that the average annual concentration of CO₂ at Mauna Loa in Hawaii will be 1.97 ± 0.52 parts per million (ppm) higher in 2023 than in 2022. Without the masking effect of La Niña, the increase would be 2.3 ppm. parts per million.

Professor Betts added: “At first glance, this year’s CO₂ increase may appear to be in line with the 1.5°C global warming limit scenario, but this is actually a false impression. It only happens temporarily, and for the wrong reasons. Once the current La Niña subsides, its ability to absorb carbon dioxide will be lost, allowing atmospheric CO₂ to rise faster.

“The 1.5°C scenario requires some annual reduction in the rate of increase in atmospheric CO₂, starting immediately and reaching zero in the 2030s.

“Achieving this goal requires rapid and large-scale reductions in global emissions. They are not reflected in current global commitments and policies, as reported in the IPCC WG3 report.”

Atmospheric concentration of carbon dioxide 2023

The forecast predicts that the average concentration of carbon dioxide this year will exceed 420 ± 0.5 ppm (parts per million) at the observation station in Mauna Loa in 2023. This will be the first time such levels have been reached in the ‘Keeling Curve Record’ which dates back to 1958. When the record began, CO₂ levels were around 316 parts per million and were increasing by less than one part per million per year.

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