The record increase adds to concerns that the natural world may become less able to absorb planet-warming gases in the long-term.

The Arctic tundra is being transformed into an overall source of CO2, thanks to warming and frequent fires, according to the US science group NOAA.

The ability of the Amazon rainforest to absorb CO2 is also being hit by drought, wildfires and deliberate deforestation.

“It’s an open question, but it’s something we need to keep a close eye on and look at very carefully,” Prof Betts tells the BBC.

The Met Office predicts the increase in CO2 concentration in 2025 will be less extreme than 2024, but still significantly off-track to meet the 1.5C target.

La Niña conditions – where surface waters in the eastern tropical Pacific Ocean are cooler than normal – have replaced El Niño, which tends to allow the natural world to take up more CO2.

“While there may be a temporary respite with slightly cooler temperatures, warming will resume because CO2 is still building up in the atmosphere,” Prof Betts says.