Atmospheric CO2 levels now 50 per cent higher than pre-industrial era

According to measurements from the National Oceanic and Atmospheric Administration (NOAA), CO2 levels peaked at 424 parts per million in May this year, an increase of 3.0ppm over the same period the year before.

The measurements were recorded at Mauna Loa Atmospheric Baseline Observatory, located on the Mauna Loa volcanic island in Hawaii. The station, which has been operating since 1958, was built there because it is 3,397 metres above sea level and located far from any continent. These factors ensure that air samples collected there represent a good average for the central Pacific. The contamination from local volcanic sources is sometimes detected at the observatory, then removed from background data.

The carbon dioxide data on Mauna Loa constitutes the longest record of direct measurements of CO2 in the atmosphere.

“Every year we see carbon dioxide levels in our atmosphere increase as a direct result of human activity,” said Rick Spinrad, the administrator of NOAA which is directly funded by the US government.

“Every year, we see the impacts of climate change in the heat waves, droughts, flooding, wildfires and storms happening all around us. While we will have to adapt to the climate impacts we cannot avoid, we must expend every effort to slash carbon pollution and safeguard this planet and the life that calls it home.”

This year’s measurements were obtained from a temporary sampling site atop the nearby volcano, which was established after lava flows cut off access to the Mauna Loa observatory in November 2022.

Widely considered the premier global sampling location for monitoring atmospheric CO2, the lava flows saw the observatory's day-to-day operations abruptly suspended. The eruption buried over a mile of access road and destroyed transmission lines delivering power to the campus.

After a 10-day interruption, NOAA restarted greenhouse gas observations in December last year using a temporary instrument installation on the deck of the University of Hawaii observatory.

Continuous daily samples were obtained from both Mauna Loa and Mauna Kea by Scripps during May - the month when CO2 levels in the Northern Hemisphere reach their maximum levels for the year.

CO2 levels in the Northern Hemisphere typically fall during the growing season and rise as plants die back in the autumn. These fluctuations are known as the Keeling Curve, named after Charles Keeling who led the creation of the Mauna Loa Observatory.

NOAA began measurements in 1974 and the two research institutions have made complementary, independent observations ever since.

Keeling’s son, geochemist Ralph Keeling, runs the Scripps program, including the sampling at Mauna Loa.

“What we’d like to see is the curve plateauing and even falling because carbon dioxide as high as 420 or 425 parts per million is not good,” Keeling said. “It shows that as much as we’ve done to mitigate and reduce emissions, we still have a long way to go.”