Largest Year–Over-Year Gain in Keeling Curve Set in March

Robert MonroeAnnouncement, Measurement Notes

Image: Adi Khen/Scripps Oceanography

Image: Adi Khen/Scripps Oceanography

New record for largest 12-month gain in carbon dioxide concentration ever observed

The monthly average concentration of carbon dioxide in the atmosphere measured at NOAA’s Mauna Loa Observatory in March 2024 was 4.7 parts per million (ppm) higher than that recorded in March 2023, setting a new record and revealing the increasing pace of CO2 addition to the atmosphere by human activities.

The previous year-over-year gain of any monthly average was a jump of 4.1 ppm from June 2015 to June 2016. As in that year, strong El Niño conditions influenced global weather patterns causing a temporary boost in CO2 levels.

“We sadly continue to break records in the CO2 rise rate,” said Ralph Keeling, director of the CO2 Program at UC San Diego’s Scripps Institution of Oceanography. “The ultimate reason is continued global growth in the consumption of fossil fuels.”

CO2 concentration tends to rise especially fast towards the end of El Niño events.  Previously the most rapid growth rate of the greenhouse gas occurred in early 2016 at the tail end of El Niño season. El Niño growth surges have been happening on top of the long-term increase in CO2 growth tied to rising fossil fuel emissions, which have increased five percent from 2016 to today.

This acceleration is significant because while CO2 itself does not provide heat, as a greenhouse gas it increases the atmosphere’s ability to trap heat that would otherwise be released into space. This excess CO2  can remain in the atmosphere for decades to centuries. Excess CO2  also has impacts beyond the atmosphere – as the ocean absorbs this excess CO2, scientists are measuring the increasing acidification of the ocean.

The gap between March 2023 and March 2024 was widened with help from  an unusual dip in the March 2023 record compared to neighboring months. But the record from earlier in 2024 shows that the current growth rate is outstripping that seen during the 2016 El Niño. The increase from February 2023 to February of this year was 4.0 ppm, compared to 3.7 for the 2016 El Niño. The increase from January 2023 to January of this year was 3.4 ppm, compared to 2.6 for the 2016 El Niño.

The growth rate from April 2023 to April 2024 dropped to 3.6 ppm, but taking into account the first four months of 2024, the growth rate is well above that for 2016. If this El Niño follows the pattern of the last El Niño, the world might experience a very high growth rate for several more months, Keeling said.

“This recent surge shows how far we still need to go to stabilize the climate system,” Keeling said. “Stabilization will require that CO2 levels start to fall. Instead, CO2 is rising faster than ever.”

Keeling Curve data for early 2023 was collected at the peak of Maunakea on the island of Hawaii, where measurement equipment had been installed following the November 2022 eruption of Mauna Loa. The Maunakea record has continued in parallel with the Mauna Loa record and the two records show excellent agreement, Keeling said.

Learn more about how carbon dioxide contributes to climate change here: