What was the average atmospheric CO2 concentration in 2023?

The average atmospheric carbon dioxide concentration in 2023 was 419.3 parts per million, or ppm. This is a global annual average, meaning that roughly 419 out of every million molecules of dry air were carbon dioxide, averaged across the year.

The figure came from measurements compiled by atmospheric-monitoring organizations, including NOAA and the Global Carbon Project. It was about 2.8 ppm higher than the 2022 average and approximately 50% above the pre-industrial concentration, which was about 280 ppm around 1750. The increase is primarily associated with fossil-fuel burning, cement production, land-use change, and deforestation.

Carbon dioxide is a small fraction of the atmosphere, but it strongly affects climate because it absorbs outgoing infrared radiation. It also remains influential for a long time: some emitted carbon is absorbed by oceans and ecosystems, while the remainder can persist in the atmosphere and contribute to warming for centuries or longer.

The number should not be confused with the Mauna Loa monthly or daily reading, which fluctuates seasonally and can differ from the global annual average. Nor is 419.3 ppm a temperature measurement; it is a concentration of a greenhouse gas.