The Mauna Loa Observatory in Hawaii has been recording atmospheric carbon dioxide levels since 1958
FRED ESPENAK/SCIENCE PHOTO LIBRARY
The level of carbon dioxide in the atmosphere measured by a weather station at the Mauna Loa Observatory in Hawaii increased by 3.58 parts per million in 2024 – the biggest jump since records began there in 1958.
“We’re still going in the wrong direction,” says climate scientist Richard Betts at the Met Office, the UK’s weather service.
The record increase is partly due to CO2 emissions from fossil fuel burning and other human actions, such as cutting down forests, hitting a record high in 2024. Adding to this were a large number of wildfires, fuelled by record-smashing global temperatures boosted by the El Niño weather pattern on top of the long-term warming.
Betts is forecasting that atmospheric CO2 levels as measured at Mauna Loa will this year rise by 2.26 parts per million (ppm), with a margin of error of 0.56 ppm either way. That’s a lot less than the 2024 record, but it will take us above the last possible pathway for limiting the increase in global surface temperatures to 1.5°C above preindustrial levels.
“You could regard it as another nail in the coffin of 1.5°C,” says Betts. “That’s now vanishingly unlikely.”
The level of CO2 in the atmosphere is the most important measure when it comes to climate change, because rising atmospheric CO2 is the main factor driving both short and long-term warming. The first ongoing measurements of CO2 levels were made at Mauna Loa.
“Because this station has the longest time record and is also located far away from the main anthropogenic and natural emissions and sinks of CO2, it is often used to represent global change in CO2 concentrations,” says Richard Engelen at the EU’s Copernicus Atmosphere Monitoring Service.
With observations from satellites, however, it is now possible to directly measure the average global level of atmospheric CO2. According to CAMS, it rose by 2.9 ppm in 2024. That isn’t a record, but it is one of the biggest increases since satellite observations began.
“The reason for this larger increase needs further investigation, but it will be a combination of rebounding of emissions in large parts of the world after the covid pandemic in combination with interannual variations in the natural carbon sink,” says Engelen. The carbon sink refers to the oceans and ecosystems on land, which have been soaking up around half of the CO2 emissions caused by humans.
It has long been predicted that, as the planet warms, less of this excess CO2 will be soaked up. “Whether this is the start of that is the concerning thing,” says Betts. “We don’t know.”
At Mauna Loa, the increase in CO2 is higher than the average global level due to the large number of wildfires in the northern hemisphere in 2024, says Betts. It takes time for plumes of CO2 from sources such as wildfires to mix evenly into the atmosphere around the world. “The fire emissions in the northern hemisphere were particularly large last year,” he says.
Although it now looks certain that global warming will pass the 1.5°C limit, Betts thinks it was still right to set that as a target. “The Paris Agreement was carefully phrased – to pursue effects to limit warming to 1.5. It was recognised at the outset that it would be challenging,” he says. “The idea was to have this stretch target to motivate action, and actually I think that was successful. It did galvanise action.”
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