NASA scientists came up with an ingenious way to weigh land masses on earth using two satellites in space, which allowed them to document Greenland’s staggering weight loss from melted ice.
Greenland has lost 5 trillion tons of weight since the early 2000s, said Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory. Willis’ team weighed Greenland starting in 2002 using two satellites, dubbed Grace and Grace FO (for follow-on).
“This satellite, Grace, and its successor, Grace Follow-On, have been measuring ice loss in Greenland since the early 2000s,” Willis said in a lecture hosted by the California Institute of Technology, “and in that time Greenland has lost more than 5 trillion tons of ice, so it’s on Jenny Craig for sure.”
Grace FO chases Grace around the planet.
“Whenever one goes over something heavy the pull of gravity causes it to speed up just a little bit,” Willis said. “Then when the second one follows it sort of catches up a little bit. They’re actually named Tom and Jerry by some of the team because they chase each other—but what we do is we measure the distance between these very, very accurately, and by watching them move apart and together we can actually weigh the land, and we can weigh things like the island of Greenland.”
The team was also able to determine where Greenland is losing ice—at the edges of its ice sheet, where the ice meets the warming ocean.
“Essentially we were able to confirm this hypothesis that the oceans were playing a huge role in melting away the ice from the edges,” Willis said.
Through a mission dubbed Ocean Melting Greenland (OMG), the team documented the process by which Greenland is losing its ice, showing not just that the melt is occurring where the ice meets the ocean, but why it’s occurring more and more rapidly.
At the same time, another series of NASA missions—Poseidon and JSON 1, 2, and 3— has documented the rising rate of sea level rise.
“The rate of rise is also increasing,” Willis said. “If you look at the first 10 years, it’s about two millimeters per year. The middle 10 years it’s about three. The last 10 years is four and maybe even four-and-a-half millimeters per year. The rate of rise is increasing, so we’re watching the oceans actually rise at a faster and faster rate.”
If Greenland were to lose all of its surface ice, he added, global sea levels would rise by almost 25 feet.