What Are CO₂ Levels Today?
The concentration of carbon dioxide in the atmosphere, measured weekly at Mauna Loa, with the trend and how far it has moved.
150.10 ppm above the 1800s level — a rise of 54% over the pre-industrial baseline.
Why the number dips every autumn
On 8 September 2026 the global average read 424.08 ppm along the seasonal curve, while the de-seasonalised trend stood at 427.89 ppm. The gap is not measurement error: most land plants are in the northern hemisphere, so they pull CO₂ out of the air through the northern growing season and give it back in autumn. The concentration peaks around May and bottoms out around September.
A falling reading in August therefore says nothing about emissions. The trend line, which removes the cycle, is the one to watch — and it has not fallen in any year of the record.
And how much warmer?
NASA GISTEMP, global surface temperature against the 1951–1980 average.
Where these come from
The headline figure is the weekly mean at NOAA’s Mauna Loa Observatory in Hawaii — the record the Keeling Curve is drawn from, running since 1958 and the longest direct measurement of atmospheric CO₂ there is. The global trend comes from NOAA’s wider baseline network, and the temperature anomaly from NASA GISS (GISTEMP v4) against a 1951–1980 average.
NOAA marks the most recent months preliminary until quality control is complete, so the last few values can be revised slightly. Everything on this page is published free by both agencies.