Melting Antarctic Ice Could Actually Slow Sea Level Rise

Rising the land beneath Antarctica’s ice sheet could slow ice loss and reduce sea level rise for centuries to come. But if emissions continue to rise, the effect could raise sea levels even more than the ice melt.

The discovery comes from a model that simulates the mantle, the layer beneath Earth’s crust, in greater detail than ever before. As the ice melts, the weight of Antarctica shrinks, and the elastic mantle below rebounds, causing the land above it to rise. As the ice melts, the weight of the continent shrinks, and the Earth’s elastic mantle rebounds, causing the land above it to rise. The rebounding land can slow the flow of the ice sheet where it meets the ocean. This “sea level feedback” occurs primarily because the rising land reshapes the ocean floor, limiting the thickness of the ice sheet at its edge. The thinner the ice, the less total ice flow into the ocean.

Researchers have long suspected that this effect might play a role in slowing ice loss, but it was unclear when the effect would begin or how it would vary across different parts of the ice sheet.

Natalia Gomez The research team, led by the McGill University researchers in Canada, and their colleagues modeled the relationship between melting ice and rebounding land, including mantle simulations that captured viscosity differences beneath the continents. East Antarctica sits on a thicker crust with a more viscous mantle, while West Antarctica’s rapidly melting glaciers sit on a thinner crust with a less viscous mantle. This more detailed picture of Earth’s interior is based on decades of precise measurements of ice sheet elevation changes and data on the mantle beneath Antarctica from seismic waves generated by earthquakes. “This is hard-won,” says Gomez.

In a very low emissions scenario, the researchers found that the rebounding land reduced Antarctica’s contribution to global average sea level rise by more than half a meter by 2500, compared to models that treated the land beneath the ice as solid. The effect was less significant in the moderate emissions scenario, but still reduced sea level rise substantially, starting in 2100.

But in a very high emissions scenario, the team found that land recovery would cause Antarctica to contribute an additional 0.8 metres to sea level rise by 2500. This is because the ice sheet retreated faster than the land recovered, pushing more water into the rest of the ocean as the seafloor rose.

“From a modeling perspective, this is a huge advancement,” he said. Alexander Bradley At the British Antarctic Survey, he says, it was always assumed that land rebound would reduce sea level rise, but this high-resolution modelling shows that the effect depends on emissions. “The changes that are happening in the 21st and 22nd centuries are actually being solidified by what we are doing now,” says Bradley.

Alexander Lovell The researchers, from Georgia Tech in Atlanta, said the simulation was “very good,” but the scenario of sea level rise as land recovers is based on worst-case assumptions about emissions and the rate of glacial retreat.