VO: Using the most advanced Earth observing laser instrument NASA has
ever flown in space, scientists have made precise, detailed measurements of how the elevation
of ice sheets in Greenland and Antarctica have changed over
sixteen years. Smith: We actually see some processes at a scale that’s
almost long enough to tell us about the climate in those two places. VO: Scientists
took ice sheet elevation measurements from 2003, overlaid data
from 2019 and analyzed where the datasets
intersected in order to see where ice was lost or gained. For
example, the study definitively shows that the East Antarctic ice sheet,
the largest of all the ice sheets, is growing. Gardner: But more importantly,
what we find is that growing is more than offset by
increased losses from the West Antarctic ice sheet, which is thinning very
rapidly as it responds to warmer ocean temperatures, specifically in the
Amundsen Embayment area. Fricker: The West Antarctic side,
we’re seeing strong thinning on the ice shelves, which is causing
drawdown on the inland ice, on the grounded ice, upstream.
Most of that is being caused because of changes in ocean
heat flux underneath the ice shelves, which is causing them to thin and then
consequently, the buttressing force is being lost against the grounded
ice, and the grounded ice is then flowing faster into the ocean and causing
sea level rise. In Greenland, we’re seeing
different signatures. Again, in the center of the ice sheet in the plateau, we’re seeing
increased accumulation. So there is a slight increase of mass in the center,
but the overall signal for Greenland is one of thinning, and that is
being caused by ocean and atmospheric signals acting all around
the edges of Greenland. Smith: So we’re seeing 200 gigatonnes per
year of ice flowing into the oceans, which is enough to raise sea
level by about two thirds of a millimeter per year. VO: Combine that with
the almost 118 gigatonnes lost in Antarctica, and sea
level has risen a total of 14 millimeters over the 16 year period due
to ice sheet melt. It may seem small, but the small
changes add up. Gardner: What we expect by the end of the century
is on the order of 2, 3, maybe 4 feet of sea level
rise. And because we have all of our infrastructure that
is built around the coasts, we have a lot of vulnerability
to a meter change in sea level rise. VO: The potential impact
from sea level rise is one critical motivation for the continued study of
the mechanics driving the changes in the ice sheets. Gardner: If we can understand
those mechanisms and how they’ve played out over the last 30 years, well then we
start to look and think about how will those ice sheets respond
to what we project the climate to be into the future. [music]