The strong El Niño event of 2015-2016 provided NASA and NOAA an unprecedented opportunity to test the effectiveness of the newest observation tool to measure global atmospheric carbon dioxide concentrations — NASA’s Orbiting Carbon Observatory-2 satellite or OCO-2.Observations of carbon dioxide concentrations over the tropical Pacific from the satellite were validated by data from NOAA’s Tropical Pacific Observing System of buoys, which directly measure carbon dioxide concentrations at the surface of the ocean.