It’s all fine and good to sign a climate treaty, but how do you know whether a country is keeping its word? Track it from space. Researchers have shown that observations by Earth-orbiting instruments can be used to estimate carbon dioxide (CO₂) emissions from individual power plants. NASA’s Orbiting Carbon Observatory 2 (OCO-2; artist’s concept above), which was launched in July 2014, was designed to monitor the movement of CO₂ in and out of ecosystems worldwide. Despite the satellite’s generally broad focus, its sensors are able to measure CO₂ concentrations in the air to within about 1 part per million in areas covering 3 square kilometers or less. When the team combined OCO-2 data from selected passes over certain power plants in the United States with computer models of how emissions plumes would disperse, its estimates of those plants’ emissions fell within 17% of the actual amounts those facilities reported for those days, the researchers report this week in Geophysical Research Letters. OCO-2, by itself, returns to view any particular spot on Earth only once every 16 days. But a handful of satellites circling Earth in low-Earth, geostationary, and highly elliptical orbits would likely provide the capability to monitor CO₂ emissions from mid- and large-sized power plants, the researchers say.