"The missions are called Orbiting Carbon Observatories because they were originally designed to measure carbon dioxide in the atmosphere. But soon after they launched, scientists realized that they were also accidentally measuring plant growth on Earth.

Basically, when plants are growing, photosynthesis is happening in their cells. And that photosynthesis gives off a very specific wavelength of light. The OCO instruments in space measure that light all over the planet.

"NASA and others have turned this happy accident into an incredibly valuable set of maps of plant photosynthesis around the world," explains Scott Denning, a longtime climate scientist at Colorado State University who worked on the OCO missions and is now retired. "Lo and behold, we also get these lovely, high resolution maps of plant growth," he says. "And that's useful to farmers, useful to rangeland and grazing and drought monitoring and forest mapping and all kinds of things, in addition to the CO2 measurements.""