Antarctica melting faster than ever before posing significant threat to coastal cities, according to major study

Ice melting in Antarctica is causing sea levels to rise at a massive rate and the frozen continent has lost about 3 trillion tonnes of ice in the last 25 years.

Warning that its rate of melting is accelerating, scientists have urged nations to defend their shores against the flooding that is likely to ensue.

In the most complete picture of Antarctic ice sheet change to date, they found that over a quarter of century the melting in the region caused global seas to rise around 8mm.

Future projections suggest this figure could rise to 15cm by the end of the century – a change that would leave coastal cities in a near constant state of flooding.

“It’s not a large number so the question I get asked most often is: why does that matter?” Professor Andrew Shepherd of the University of Leeds, who led the study. “First of all, the last time we did this assessment we concluded that the ice sheet was contributing 0.2 mm per year to sea level rise.”

“In the past five years it has stepped up to 0.6 mm per year – so that’s three times faster.”

The study was accompanied by warnings from leading scientists that the world is running out of time to save it from a changing climate.

Antarctica stores enough frozen water to raise global sea level by 58 metres and knowing how fast it is melting is of grave importance for policy makers.

Scientists used to think that Antarctica was protected from melting by warm waters because of Southern Ocean circulation acting as a kind of “thermal controller”.

However, it is increasingly clear that ice loss from West Antarctica in particular is speeding up as a result of contact between the floating ice shelves and warming ocean waters.

The new study by an international team known as the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) was assembled using data from 24 long-term satellite surveys of the region’s ice sheets.

Historically, the main contributors to sea level rise are melting ice from Greenland and mountain glaciers, as well as water expanding due to higher temperatures.

Although Professor Shepherd noted that ice losses from Antarctica will tend to impact northern hemisphere countries disproportionately, it is difficult to make specific predictions for the UK and other nations.

However, he said flood defences such as the Thames barrier will have to be reconsidered as new predictions emerge about the future sea level rise.

“I think 15 cm of sea level rise is a significant concern,” he said.

He added: “If you look at coastal cities like New York or San Francisco it tends to flood there when high tides coincide with storm conditions."

Noting that such floods occur roughly once every year, he said: “If you raise the level by 15 cm in San Francisco it will flood 20 times a year if you don’t do anything to the sea wall, and 20 times a year in New York.”

Professor Chris Rapley, a climate scientist at University College London who was not involved in the study, said the work provided a valuable insight into the melting of Antarctica.

He compared the region to a “slumbering giant awakening” that could soon rival other sources of sea level rise.

Professor Martin Siegert, co-Director of the Grantham Institute at Imperial College, who was also not involved in the research, added: “Unfortunately, we appear to be on a pathway to substantial ice-sheet loss in the decades ahead, with longer term consequences for enhanced sea-level rise.

“If we aren't already alert to the dangers posed by climate change, this should be an enormous wake-up call.”

Professor Michiel van den Broeke of Utrecht University, a member of the IMBIE team, said that while preparations for flooding are already underway in his native Netherlands, news about Antarctica would force policy makers to “recalibrate” these plans.

Their IMBIE study appeared in the journal Nature alongside a series of studies looking at the past and future of Antarctica in a changing climate, including work looking at the impact of storms on the deterioration of ice shelves.

In a one of these papers, Professor Siegert and his colleagues presented two future scenarios in which Antarctica is either protected from or exposed to unrestricted greenhouse gas emissions and exploitation.

“Antarctic is being affected by global warming, and unless we curtail our carbon dioxide emissions within the next decade, and have a zero carbon economy within a few decades, we will be locked into substantial global changes, including those in Antarctica and the Southern Ocean,” he said.