An international team of scientists from over 40 organizations around the world has completed the most comprehensive assessment of how Antarctica's ice mass is changing – and as expected, the results are worrying. The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) shows that the rate of ice loss – and the resulting sea level rise – has tripled since 2012, compared to a more steady rate over the last 25 years.

This latest assessment involves 84 scientists from more than 40 institutions, and combines data from 24 satellite surveys. It follows in the footsteps of the first IMBIE conducted in 2012, and paints a particularly grim picture of the years between then and 2017.

The team studied changes in the ice mass of Antarctica between 1992 and 2017, and the associated contributions to the rising sea level. Before 2012, Antarctic ice was receding at a relatively steady rate of about 83.8 billion tons a year. In the years after that, the annual ice loss appears to have accelerated to a rate of 241.1 billion tons – around three times the previous rate.

Of course all that ice has to go somewhere, and the resulting sea level rise has also accelerated. The IMBIE researchers say that the sea level has climbed by 7.6 mm (0.3 in) since 1992, with almost half of that amount – 3 mm (0.12 in) – occurring in the five years between 2012 and 2017.

"We have long suspected that changes in Earth's climate will affect the polar ice sheets," says Andrew Shepherd, co-lead researcher on the project. "Thanks to the satellites that our space agencies have launched, we can now track their ice losses and global sea-level contribution with confidence. According to our analysis, there has been a step increase in ice losses from Antarctica during the past decade, and the continent is causing sea levels to rise faster today than at any time in the past 25 years."

West Antarctica has been the hardest hit, losing 175.3 billion tons of ice per year since 2012 – up from 58.4 billion tons a year during the 1990s. The Antarctic Peninsula in the north saw an increase of 27.6 billion tons each year since the beginning of the century, including the giant iceberg that broke off from the Larsen C ice shelf last year.

Interestingly, the East Antarctic ice shelf fared better, actually gaining about 5.5 billion tons of ice each year on average. Unfortunately, that's a drop in the bucket compared to the speed with which the rest of the continent is melting.

"Satellites have given us an amazing, continent-wide picture of how Antarctica is changing," says Pippa Whitehouse, an author on the study. "The length of the satellite record now makes it possible for us to identify regions that have been undergoing sustained ice loss for over a decade. The next piece of the puzzle is to understand the processes driving this change. To do this, we need to keep watching the ice sheet closely, but we also need to look back in time and try to understand how the ice sheet responded to past climate change."

The latest findings are discussed in the IMBIE video below.

The research was published in the journal Nature.

Sources: ESA, JPL

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