Keeling Curve Begins Measuring CO2

In 1958, American scientist Charles David Keeling installed instruments atop Mauna Loa in Hawaii to continuously measure atmospheric carbon dioxide. The resulting graph — the Keeling Curve — became the single most important dataset in climate science. It showed an unmistakable upward trend: CO2 was rising year after year, from 315 parts per million in 1958 to over 420 ppm by the 2020s, with a distinctive sawtooth pattern reflecting seasonal plant growth. The Keeling Curve provided irrefutable evidence that human activity was changing the composition of Earth's atmosphere. Keeling fought for decades to maintain funding for these measurements, and his persistence created the empirical backbone of climate science.