Ice melt in Antarctica is not consistent, new analysis finds

Antarctic ice is melting, bringing massive amounts of water to the world’s seas and causing them to rise – but this melting is not as linear and consistent as scientists previously thought, shows a new analysis of 20 years of satellite data.

The analysis, based on gravitational field data from a NASA satellite system, shows that Antarctic ice melts at different rates each year, which means that the models that scientists use to predict the upcoming sea level rise may also need to be adjusted.

“The ice sheet doesn’t change with a constant rate – it’s more complicated than a linear change,” said Lei Wang, assistant professor of civil, environmental and geodetic engineering at Ohio State University and main author of the analysis. “Change is more dynamic: the speed of melting changes with time.”

The research was published in Geophysical research letters and presented at the American Geophysical Union Fall Meeting in December.

The researchers’ analysis is based on data from NASA’s Gravity Recovery and Climate Experiment (GRACE), a two-satellite mission that measures changes in the world’s oceans, groundwater and ice caps.

Models that predict sea level rise are generally built around the assumption that ice is melting from the world’s largest ice fields in Antarctica and Greenland at a constant rate.

But this analysis found that, as the mass of ice on the Antarctic ice sheet changes seasonally and annually, these projections are not as reliable as they could be. Extreme snowfall over a year, for example, could increase the amount of ice in Antarctica. Changes in the atmosphere or in the surrounding ocean could decrease it for another year.

Overall, Wang said, the volume of ice in Antarctica is declining. But a chart of the decline on a line chart would have peaks and troughs depending on what happened in a given time period.

To understand these changes, Wang and the other researchers evaluated data on the gravitational field between satellites over Antarctica and ice on the mainland. Changes in the mass of the ice – either increases in heavy snowfall or decreases in melting – change this gravitational field.

From 2016 to 2018, for example, the West Antarctic ice sheet actually increased a bit due to massive snowfall. During this same period, however, the East Antarctic ice sheet shrank due to the melt.

“I am not saying that the ice melt in Antarctica is not an acute problem – it is still very acute,” Wang said. “All of Antarctica is losing mass, very quickly. It’s just a time scale issue and a rate issue, and our models that predict sea level change should reflect that.”