More than 60 years ago, atmospheric scientist Charles David Keeling began regular measurements of carbon dioxide concentrations in the atmosphere. In the heart of the Pacific and far from the largest human sources of the gas, Hawaii’s Mauna Loa Observatory was an ideal location for these measurements. Within just two years, Keeling had detected two patterns in the data. The first was an annual rise and fall as the seasons came and went. But the second — a year-by-year increase — suggested something alarming: a rise in carbon dioxide produced by the widespread burning of fossil fuels. In 1965, Keeling’s measurements were incorporated into a report for U.S.