The Mauna Loa Curve
On a volcano in Hawaii, a single instrument has measured atmospheric CO₂ every day since 1958. This is what it has recorded.
This is atmospheric carbon dioxide, measured every day for the last five years on a volcano in Hawaii.
It looks orderly. It is not.
Zoom out.
Charles David Keeling started these measurements in March 1958, at 313 parts per million. They have not paused — for war, recession, pandemic, or politics. The line climbs roughly 2.5 ppm every year. There is no year on this chart in which it did not.
Look closely at the curve. It breathes.
CO₂ falls through the northern-hemisphere summer and rises through the northern-hemisphere winter — that's the planet's plants, photosynthesising and respiring on a six-month cycle. Most of the Earth's land sits north of the equator, so the planet's lungs are northern. It exhales each May. It inhales each October.
Step back out. The line isn't straight.
In the 1980s, atmospheric CO₂ at Mauna Loa rose by about 14 parts per million. In the 2010s, it rose by 22 — more than half again as much in the same span of time.
The acceleration is the thing that should worry you, not the absolute level.
By 1988, the annual average at Mauna Loa had passed 350 parts per million — a level some scientists once argued we should not exceed if we wanted to preserve the climate of the twentieth century.
It crossed 400 in 2015. It crossed 420 in 2023.
The line keeps climbing. There is no mechanism, on any timescale shorter than centuries, that puts it back.
The most recent readings sit above 430 ppm.
The instrument is still running. Every day adds a new measurement. The chart you're watching updates automatically — what you see is, at most, two days old.
This is the longest continuous direct measurement of an environmental variable in scientific history.
It is, by some accounts, the single most consequential graph ever produced.
Now you know what it shows.