New York, Feb 2 (IANS): Antarctic ice is melting, contributing massive amounts of water to the world's seas and causing them to rise, but that melt is not as linear and consistent as scientists previously thought, a new study suggests.

The analysis, of 20 years' worth of satellite data, shows that Antarctica's ice melts at different rates each year, meaning the models scientists use to predict coming sea level rise might also need adjusting.

"The ice sheet is not changing with a constant rate -- it's more complicated than a linear change," said lead author Lei Wang, Assistant Professor at the Ohio State University in the US.

The study, published in the journal Geophysical Research Letters, is built on data from NASA's GRACE (Gravity Recovery and Climate Experiment), a two-satellite mission that measures changes in the world's oceans, ground water and ice sheets.

Models that predict sea-level rise are typically built around the assumption that ice is melting from the world's largest ice fields in Antarctica and Greenland at a consistent rate.

But this analysis found that, because the mass of ice on the Antarctic Ice Sheet changes depending on the season and year, those projections are not as reliable as they could be. Extreme snowfall one year, for example, might increase the amount of ice in Antarctica. Changes in the atmosphere or surrounding ocean might decrease it another year.

Overall, the researcher said, the volume of ice in Antarctica is decreasing. But a chart of the decline on a line graph would have spikes and valleys depending on what happened in a given time period.

To understand those changes, the team evaluated data on the gravitational field between the satellites over Antarctica and ice on the continent. Changes to the ice's mass -- either increases from big snowfalls or decreases from melt -- change that gravitational field.

From 2016 to 2018, for example, the ice sheet in West Antarctica actually grew a bit because of a massive snow. During that same time period, though, the ice sheet in East Antarctica shrank because of melt.