Atmospheric CO₂
Atmospheric CO₂ has climbed to about 427.6 ppm (September 2026) — up roughly 112 ppm, about 35.4%, since records began at Mauna Loa in 1958.
Source: NOAA Global Monitoring Laboratory. Data through September 2026. Download the data (JSON).
About this indicator
Carbon dioxide is the greenhouse gas most responsible for modern global warming. It is released mainly by burning fossil fuels — coal, oil and gas — and by deforestation, and it lingers in the atmosphere for centuries.
The famous "Keeling Curve" from Mauna Loa in Hawaii has tracked CO₂ continuously since 1958. It rises and falls slightly each year as plants grow and die back, but the long-term trend is a steady, accelerating climb far above anything seen in the ice-core record of the last 800,000 years.
Why it matters: More CO₂ traps more heat near the surface, warming the planet and driving sea-level rise, more extreme weather and ocean acidification.
How to read this chart
The vertical axis is parts per million, or ppm: a reading of 400 ppm means 400 carbon dioxide molecules for every million molecules of dry air. Each point is a monthly mean rather than a single measurement, which is why the line carries a small annual wiggle — the Northern Hemisphere growing season draws CO₂ down through the summer and releases it again over the winter.
Read the slope, not the wiggle. Month-to-month movement is dominated by that seasonal cycle, while the decade-scale climb is the part that reflects accumulation. The figures on this page are a snapshot taken when the page was last built, so the newest month or two of the official record may not appear yet, and the JSON download holds the exact value behind every point on the chart.