Atmospheric carbon dioxide levels at record high

Carbon dioxide

Carbon dioxide levels are now more than 50 per cent higher than they were before the onset of the industrial era, scientists say.

Carbon dioxide levels measured at NOAA’s Mauna Loa Atmospheric Baseline Observatory peaked at 424 parts per million in May, continuing a steady climb further into territory not seen for millions of years, say scientists from NOAA and Scripps Institution of Oceanography at the University of California San Diego. 

Measurements of carbon dioxide (CO2) obtained by NOAA’s Global Monitoring Laboratory averaged 424.0 parts per million (ppm) in May, the month when CO2 peaks in the Northern Hemisphere. That is an increase of 3.0 ppm over May 2022, and represents the fourth-largest annual increases in the peak of the Keeling Curve in NOAA’s record. Scientists at Scripps, which maintains an independent record, calculated a May monthly average of 423.78 ppm, also a 3.0 ppm increase over their May 2022 average.

Carbon dioxide levels are now more than 50 per cent higher than they were before the onset of the industrial era.

“Every year we see carbon dioxide levels in our atmosphere increase as a direct result of human activity,” NOAA administrator, Rick Spinrad, said. “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.”

Carbon dioxide pollution is generated by burning fossil fuels for transportation and electrical generation, by cement manufacturing, deforestation, agriculture and many other practices. Like other greenhouse gases, CO2 traps heat radiating from the planet’s surface that would otherwise escape into space, amplifying extreme weather events, such as heat waves, drought and wildfires, as well as precipitation and flooding.

Rising CO2 levels also pose a threat to the world’s ocean, which absorbs both CO2 gas and excess heat from the atmosphere. Impacts include increasing surface and subsurface ocean temperatures and the disruption of marine ecosystems, rising sea levels and ocean acidification, which changes the chemistry of seawater, leading to lower dissolved oxygen, and interferes with the growth of some marine organisms.

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 re-powered 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 dataset for international climate scientists and a benchmark for policymakers attempting to address the causes and impacts of climate change.

Scripps Oceanography geoscientist Charles David Keeling initiated on-site measurements of CO2 at NOAA’s Mauna Loa weather station in 1958. Keeling was the first to recognize that CO2 levels in the Northern Hemisphere fell during the growing season, and rose as plants died back in the fall. He documented these CO2fluctuations in a record that came to be known as the Keeling Curve. He was also the first to recognise that, despite the seasonal fluctuation, CO2 levels rose every year. 

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.”

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