What the work claims
The work claims that atmospheric CO₂ is rising steadily and seasonally, with a distinct annual cycle tied to northern-hemisphere vegetation, and that this rise is linked to fossil fuel combustion. It presents the first monthly CO₂ records showing both features — and identifies them as evidence of rapidly increasing CO₂.
How it was done
Keeling developed the first instrument for consistently accurate atmospheric CO₂ measurement at Caltech. He used it at Big Sur to detect a rise since the 19th century. From March 1958, he made frequent, regular measurements at Mauna Loa and Antarctica. Mauna Loa was chosen for its remote location, lack of vegetation, and elevation above the thermal inversion layer. He measured the incoming ocean breeze to avoid volcanic contamination. Data were normalized to remove local effects.
What holds up
The seasonal cycle (~6 ppm amplitude) holds up. The steady rise from 313 ppm (March 1958) to 406 ppm (November 2018) holds up. The attribution of the seasonal peak to late northern-hemisphere winter — and the spring/summer decline to northern-land plant growth — holds up. The Mauna Loa record remains the longest continuous atmospheric CO₂ record and is a reliable indicator of the global mid-troposphere trend.
What does not
It does not prove causation between fossil fuel emissions and rising CO₂. It shows correlation — strong and consistent — but does not isolate or quantify individual emission sources. It does not measure CO₂ in the stratosphere, lower troposphere or near-surface boundary layer. It does not capture regional gradients or short-term spikes from fires or volcanoes beyond what normalization removes.
Why it matters beyond the lab
It matters because it transformed atmospheric CO₂ from a theoretical variable into a measured quantity. It gave climate science its first unambiguous, long-term metric. It anchors every major climate assessment. Its visibility — the curve itself — made anthropogenic climate change tangible, visible and urgent to policymakers and the public.
Is it worth your time
Yes. It delivers the longest continuous atmospheric CO₂ record — a direct, calibrated, ground-truthed measure of a planetary-scale change. Its methodology remains foundational. Its numbers anchor climate policy, modelling and public understanding. No alternative record matches its duration, consistency or validation.