Ice sheet losses from Greenland and Antarctica have outpaced snow accumulation and contributed approximately 14 millimeters to sea level rise over 16 years (2003 to 2019), a new analysis of data from NASA's laser-shooting satellites has revealed. By combining data from the first polar-orbiting space laser, ICESat, and next-generation ICESat-2, scientists here were able to account for even subtle changes in ice masses, which had been previously overlooked and resulted in small, yet significant biases on ice mass changes. The tug of war between ice mass loss and gain - highly dependent on interactions among ice, ocean, and atmosphere, increasingly affected by a warming climate - dictates contributions to sea level rise. Since the 1990s, laser-shooting satellites have provided a record of ice mass by measuring the changing height of polar ice. However, it has been challenging to form a unified estimate of mass changes (resolving differences in instruments, methodologies and study periods) in both grounded ice sheets and floating ice shelves that also accounts for the icy bodies' interactions with the atmosphere and ocean in a changing climate. Here, Ben Smith and colleagues aggregated 2018 and 2019 data from ICESat-2 to 2003 to 2008 data from ICESat. In order to form more accurate predictions, they restricted their analysis to areas covered throughout both missions and factored in several atmospheric and oceanic impacts, such as ocean tides, to raw data on height changes. They found that, while losses from Greenland and Antarctic ice shelves and glaciers were partially offset by gains via snow accumulation in East Antarctica and central Greenland, total losses outpaced the rate of gain. Lost ice was most apparent in northwest and southeast Greenland and West Antarctica; specifically, the melting of West Antarctica's floating ice shelves - a process that directly affects the rate of ice flow into the ocean - accounted for over 30% of the region's total mass loss. Their data projects melting ice from Greenland and Antarctica will increasingly contribute to sea level rise within tens to hundreds of years, the authors say.
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