Carbon dioxide (CO2) levels measured at NOAA’s Mauna Loa Atmospheric Baseline Observatory peaked at 424 parts per million (ppm) in May 2023, continuing a steady climb into territory not seen for millions of years, according to NOAA and the Scripps Institution of Oceanography at UC San Diego.
Measurements of CO2 obtained by NOAA’s Global Monitoring Laboratory averaged 424 parts per million in May, the month when CO2 peaks in the Northern Hemisphere. That represents an increase of 3.0ppm over May 2022. Scientists at Scripps Oceanography, which maintains an independent record, calculated a May monthly average of 423.78ppm. That increase is also a jump of 3.0ppm over the May 2022 average reported by the Scripps CO2 Program.
“Sadly, we’re setting a new record,” said Scripps Oceanography geoscientist Ralph Keeling, who oversees the iconic Keeling Curve record established by his father 65 years ago. “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. It shows as much as we’ve done to mitigate and reduce emissions, we still have a long way to go.”
CO2 levels are now more than 50% higher than they were before the onset of the industrial era. Rick Spinrad, NOAA Administrator, said, “Every year we see CO2 levels in our atmosphere increase as a direct result of human activity. 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, NOAA’s measurements were obtained from a temporary sampling site atop the nearby Mauna Kea volcano, which was established after lava flows cut off access to the Mauna Loa observatory in November 2022. Scripps’s May measurements were taken at Mauna Loa, after NOAA staff successfully repowered a Scripps instrument with a solar and battery system in March.
The Mauna Loa data, together with measurements from sampling stations around the world, are incorporated by NOAA’s Global Monitoring Laboratory into the Global Greenhouse Gas Reference Network, a foundational research data set for international climate scientists and a benchmark for policymakers attempting to address the causes and impacts of climate change.