Is the carbon dioxide in the air rising?

That time, that place

Into the 1950s carbon dioxide was a gas nobody measured well. Near a city the reading jumped with traffic and factories; near a forest it swung between day and night.

So nobody could say with confidence what the global figure was, or whether it was rising.

Why this question

Keeling did two things. He built a very precise instrument. And he chose where to stand.

The summit of Mauna Loa in Hawaii: 3,400 metres up, ocean in every direction, no city or forest nearby. A place where you measure air that has already mixed globally.

And he measured every day. From 1958 until now.

What was found

The curve showed two things.

One is a saw-tooth: down each spring, up each autumn. Most land is in the northern hemisphere, so as its plants leaf out they draw carbon dioxide down, and as leaves fall they give it back. The planet breathing.

The other is that the whole saw-tooth climbs. From 315 ppm in 1958, it has risen every single year.

The Keeling curve became the starting point of climate discussion. For one fact to be beyond dispute, somebody has to stand in the same place and measure every day. The funding nearly stopped more than once.