Melting Antarctic ice could slow sea level rise

Uplifting the land beneath the Antarctic ice sheet could help slow ice loss and limit sea level rise over the coming centuries, but if emissions continue to rise, it could cause more sea levels to rise than the ice melt alone.

The findings come from a model that simulates Earth’s mantle, the layer beneath the crust, in more detail than ever before. When Antarctica loses its weight as ice melts, the elastic mantle beneath it bounces back, causing the land above it to rise. When ice melts and the continents lose their weight, Earth’s elastic mantle bounces back, causing the land above it to rise. The bounced back land can slow the flow of ice sheets where they meet the ocean. This “sea-level feedback” occurs primarily because the uplifted land changes the shape of the ocean floor, limiting the thickness of the ice sheet’s edges. Thinner ice there reduces the overall inflow of ice into the ocean.

Researchers have long suspected that this effect plays a role in slowing ice loss, but it was unclear when this effect begins or how it varies in different parts of the ice sheet.

Natalia Gomez Gomes and his colleagues at McGill University in Canada modeled the relationship between the melting ice and the rebounding land, and also simulated the mantle, capturing the different viscosities beneath the continents: East Antarctica sits on a more viscous mantle and thicker crust, while West Antarctica’s rapidly melting glaciers sit on a less viscous mantle and thinner crust. This more detailed picture of Earth’s interior is based on precise measurements of ice sheet elevation changes over decades, as well as data about the mantle beneath Antarctica from seismic waves generated by earthquakes. “This is hard-earned,” Gomes says.

The researchers found that under a very low emissions scenario, compared to a model that considered the ground beneath the ice solid, land uplift would reduce Antarctica’s contribution to global mean sea level rise by more than 50 centimetres by 2500. This effect was less pronounced under a moderate emissions scenario, but still led to a large reduction in sea level rise, with effects starting to be felt as early as 2100.

But in a very high emissions scenario, the team found that land uplift in Antarctica would raise sea levels by an additional 0.8 metres by 2500. This happened because the ice sheet retreated faster than land uplift, and the rising sea floor pushed more water into the rest of the ocean.

“From a modeling perspective, this is a huge step forward.” Alexander Bradley The British Antarctic Survey’s Bradley says it’s always been thought that land uplift would limit sea-level rise, but this high-resolution modelling shows that the effect depends on emissions. “The changes that occur in the 21st and 22nd centuries will depend very much on what we do now,” he says.

Alexander Lovell Researchers at the Georgia Institute of Technology in Atlanta call it a “very good simulation,” but the scenario in which land uplift drives sea level rise is based on worst-case assumptions about emissions and the rate at which ice sheets are retreating.