It took a lot of political resolve for nearly 200 nations to negotiate the historic Paris climate agreement to cut greenhouse gas emissions. It also required something else.

“COP21 itself would have been impossible without satellites,” said Jean Yves Le Gall, the president of the French space agency, CNES.

Around the world, more than 160 satellites beam data to scientists studying climate. The data empowers political leaders to base climate decisions on science rather than conjecture. U.S. space agency NASA operates a number of these satellites, as well as special aircraft, to study climate change from the sky.

Want to know how?

The Flagship: Terra

Artistic rendition of satellite (NASA)
NASA’s Terra satellite (NASA)

About the size of an average bus, Terra is the flagship of NASA’s Earth Observing System. Its instruments can observe water, carbon and energy cycles by studying the atmosphere, ocean, land, snow and ice.

The “A-Train”

Artistic rendition of satellites in orbit and their ranges of Earth (NASA)

Because the “afternoon constellation” of satellites rushes down the same orbital track, scientists have dubbed it the “A-Train.” Leading the pack is Orbiting Carbon Observatory-2, which was launched in July 2014. It’s the first operational satellite dedicated to studying atmospheric carbon dioxide. The A-Train can combine data from different satellites to help scientists learn even more.

Operation IceBridge

Aircraft flying over water showing wing and engines (NASA)

Aircraft-based sensors also contribute to NASA’s climate research. Here, a specially designed NASA DC-8 flies over the Pine Island Glacier ice shelf in Antarctica as part of Operation IceBridge, which measures the rapid melting of polar ice.

Putting it all together

Two people talking and silhouetted against world map showing climate data (NASA)

At NASA’s Goddard Space Flight Center in Maryland, former astronaut Piers Sellers (left) discusses climate change with actor Leonardo DiCaprio. The two are standing in front of Goddard’s “Hyperwall,” which displays scientific data captured by NASA’s fleet of satellites. NASA’s Earth Sciences Division operates space technology and makes its research available to citizens and scientists around the world.