The OCO-2 satellite can measure photosynthesis, as well as the amount of CO 2 in the atmosphere, and so will shed new light on the carbon cycle. PHOTO: BEAWIHARTA/REUTERS/NEWSCOM

One of the crowning achievements of modern environmental science is the Keeling curve, the detailed time series of the concentration of atmospheric carbon dioxide (CO 2 ) begun in 1958 that has enabled deep insights into the mechanisms of global climate change. These measurements were difficult to make for most of their 60-year history, involving the physical collection of air samples in flasks at a small number of sites scattered strategically around the globe and the subsequent analysis of their CO 2 inventories in a handful of laboratories throughout the world. The Orbiting Carbon Observatory-2 (OCO-2) mission was designed to circumvent those limitations by providing a platform with which atmospheric CO 2 can be measured spectrally from space over large geographic areas, thereby offering an unprecedented capability to study, in great detail, the processes that affect the concentration of the gas over a variety of spatial and temporal scales. The satellite can also measure solar-induced fluorescence, a proxy for photosynthesis, which provides valuable information about the biological processes that affect atmospheric CO 2 .

In this issue, a collection of Research Articles presents the initial results from OCO-2, covering the detection of CO 2 emissions from specific point sources; measurements of CO 2 variations associated with El Niño, on land and at sea; and solar-induced fluorescence measurements of photosynthesis for determining gross primary production by plants. With its impressive collection of observational capabilities, OCO-2 will enable measurements of atmospheric CO 2 to be made with sufficient precision, resolution, and coverage to faithfully characterize its sources and sinks globally over the seasonal cycle, a long-standing goal in atmospheric and climate science.