Imagine how much water flows through the Colorado River each year. Now multiply that by six. According to NASA geophysicists who recently adjusted measurements from a massive geological satellite, that's how much freshwater is melting from Greenland's glaciers each year—the latest confirmation of a sea change disaster Seniorhelpline warned of earlier this fall.
By measuring the shifting distance and speed between two Gravity Recovery and Climate Experiment (GRACE) satellites, scientists calculated the glaciers' diminishing pull on Earth to discover that they were losing approximately 41 cubic miles each year. The heavy melting is consistent with predictions of climate warming's effect on the continent and could have serious consequences, says Scott Luthcke of the Planetary Geodynamics Laboratory at NASA's Goddard Space Flight Center.
The dissipating glaciers are contributing not only to rising sea levels worldwide but also possibly to the slowdown of the subpolar gyre—the dominant current that brings Europe its mild climate. The gyre is driven by cold, dense salt water that sinks to the bottom of the ocean and fuels a kind of liquid conveyor belt. "If you're dumping a lot of this more buoyant freshwater in, one of the more immediate concerns is how soon, and can it, change the dominant circulation in the northern Atlantic," Luthcke says.
Changes in the rate between the pair of orbiting GRACE satellites depend on the level of pull, or gravity, from objects on Earth, which then can be used to determine the mass of those objects. Generally, gravity fields are measured every 30 days, but for this study, Luthcke and his team collected data locally every 10 days, which helped them determine exactly when particular glacier areas began to lose or accumulate mass.
The GRACE study of Greenland will run indefinitely in order to gather as much data as possible, but the same scientists are also using monitoring mass change in Antarctica, where the team is observing similar mass shedding at the low-elevation regions. Their ultimate goal is to observe other, more geologically challenging areas, like the Alaskan mountain glaciers. –Erin McCarthy
Freshwater melt from the Greenland ice sheet contributes to a layer of buoyant water that is beginning to cap the North Atlantic Ocean. PHOTOGRAPH BY BLICKWINKEL/ALAMY (CLICK TO ENLARGE)