Daily Beast has more on how 204 billion tons of melting glaciers have changed the way our planet’s gravity works:
Between 2009 and 2012, the years for which GOCE was taking data, the amount of gravity in Antarctica decreased noticeably, corresponding to a lot of ice melt.
From the point of view of artificial satellites or the Moon, Earth’s gravity is mostly a steady influence, a tug that doesn’t particularly depend on where the satellite is over Earth’s surface. However, mass is the source of gravity, so if the crust is thicker in one place than another—say, the Himalayas vs. the floor of the Atlantic Ocean—the thicker part will exert a slightly higher gravitational pull.
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The authors of the new paper looked at GOCE and GRACE data for three Antarctic glaciers, and found they are losing approximately 185 billion metric tons (204 billion US tons) of ice each year for the three years of the study. For comparison, all the humans put together weigh approximately 287 million metric tons (316 million US tons)—each of the three glaciers loses more ice mass than the combined weight of humanity.
As someone who researched gravity in graduate school (though more things like black holes than the Earth geoid), I find the fact that we can measure ice loss using gravitational satellites really fascinating even as I’m disturbed by what we discover. But that’s exactly why we do science of this kind: we have to understand the magnitude of the problem.