Atmospheric levels of the three most important human-made greenhouse gases - carbon dioxide, methane, and nitrous oxide - continued their steady climb during 2023, according to the latest measurements from NOAA and CIRES scientists. 

Concentrations of heat-trapping gases are measured regularly by NOAA’s Global Monitoring Laboratory (GML). Looking back at 2023, GML scientists found the global average surface concentration of carbon dioxide, averaged over the year, was 419.3 parts per million (ppm). In 2023, the annual increase in carbon dioxide was 2.8 ppm. 

This was the 12th consecutive year carbon dioxide increased by more than 2 ppm, extending the highest sustained rate of carbon dioxide increases during the 65-year monitoring record. Atmospheric carbon dioxide is now 50 percent higher than pre-industrial levels.

“The 2023 increase is the third-largest in the past decade, likely a result of an ongoing increase of fossil fuel carbon dioxide emissions, coupled with increased fire emissions possibly as a result of the transition from La Nina to El Nino,” said Xin Lan, a CIRES scientist who leads those greenhouse gas measurements at GML to track global greenhouse gas trends. 

Atmospheric methane, which is less abundant than carbon dioxide but more potent at trapping heat in the atmosphere, rose to an average of 1922.6 parts per billion (ppb). The 2023 methane increase was 11.1 ppb, lower than the record growth rates seen in 2020 (15.15 ppb), 2021 (17.97 ppb), and 2022 (13.16 ppb), but still the 5th highest since renewed methane growth started in 2007. Atmospheric methane levels are now more than 150 percent higher than their pre-industrial levels.

In 2023, levels of nitrous oxide, the third-most significant anthropogenic greenhouse gas, climbed by 1 ppb to 336.7 ppb. Increases in atmospheric nitrous oxide during recent decades are mainly from the use of nitrogen fertilizer and manure from the expansion and intensification of agriculture. Nitrous oxide concentrations are now 25 percent higher than pre-industrial levels of 270 ppb. 

Tracking greenhouse gas levels

GML scientists and partners collected more than 15,000 air samples from monitoring stations around the world in 2023 and analyzed their greenhouse gas levels in GML’s state-of-the-art laboratory in Boulder, Colorado. 

A subset of these measurements from clean marine surface environments are used to calculate global average levels of these three primary, long-lived greenhouse gases. Each spring, NOAA and CIRES scientists release preliminary calculations of the global average greenhouse gas levels observed during the previous year.

“NOAA’s long-term air sampling program is essential for tracking causes of climate change and for supporting the U.S. efforts to establish an integrated national greenhouse gas measuring, monitoring, and information system,” said GML Director Vanda Grubišić. “As these numbers show, we still have a lot of work to do to make meaningful progress in reducing the amount of greenhouse gases accumulating in the atmosphere.” 

By far the most important contributor to climate change is carbon dioxide, which is primarily emitted by burning of fossil fuels. About a quarter of the carbon dioxide emissions from fossil fuels to date have been absorbed by the world’s oceans, contributing to ocean acidification, which may threaten some fisheries and aquaculture around the world. The oceans have also absorbed an estimated 90 percent of the excess heat trapped in the atmosphere by greenhouse gases. 

NOAA's measurements show that atmospheric methane increased rapidly during the 1980s, nearly stabilized in the late 1990s and early 2000s, then resumed a rapid rise in 2007. The exact causes of the recent increase in methane are not yet fully known, according to Lan. One possibility, she said, is the influence of a persistent three-year La Niña (2020 - 2023), which, on average, results in enhanced precipitation over Earth’s wetland regions, which may increase the activity of microbes that generate methane emissions as a result. NOAA and CIRES scientists are also investigating the possibility that climate change is causing wetlands to give off increasing methane emissions in a feedback loop.