Friday, 22 June, 2018

'Deeply concerning': Antarctic ice loss triples

Sandy Nunez | 14 June, 2018, 06:05

"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", says Earth observation scientist Andrew Shepherd from the University of Leeds, UK.

Millimeters of sea level rise may not sound like much, but previous surveys suggested that Antarctica's massive ice sheets likely wouldn't be affected by climate change at all.

Antarctica's ice sheet is melting at rapidly increasing rate, now pouring more than 200 billion tons of ice into the ocean annually and raising sea levels a half millimeter every year, a team of 80 scientists reported Wednesday.

Antarctica has lost trillion tonnes of ice to global warming over the past quarter of a century, according to a new study, and that loss has been accelerating in recent years, to triple the rate that was seen prior to 2012. Meanwhile, in the Antarctic Peninsula, the annual rate of ice loss increased from around 7 billion tons from 1992 to 2012 to 36 billion tons from 2012 to 2017, largely due to collapsing ice shelves.

A single millimeter of global sea level rise is equivalent to 360 billion tons of melted ice, or an imaginary enormous ice cube with sides about 4.35 miles long.

However, he said that there is growing evidence that projections of Antarctica's influence on sea-level rise may have been underestimated.

Scientists have previously raised fears about a scenario in which ice loss from Antarctica takes on a rate of explosive growth.

More than 90% of that frozen water sits atop East Antarctica, which has remained mostly stable even as climate change has driven up Earth's average surface temperature by a full degree Celsius (1.8 degrees Fahrenheit). However, in the last five years, it too has begun to lose ice, perhaps as much as 28 billion tons per year, although the uncertainty surrounding this number remains high.

Per the team's calculations, a high emissions scenario - in which carbon emissions rise unabated and environmental protections in Antarctica are not implemented - global air temperature would rise almost 3.5°C above 1850 levels by 2070, with sea level rise averaging somewhere between 10-15 mm every year.

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Since 1992, scientists found that ice losses contributed to a sea level rise of 0.76 cm.

The researchers attribute the increased losses in West Antarctica and the Antarctic Peninsular to changes in regional floating-ice shelves, which can provide a buffer to continental-ice sheets. "If this kind of thing happens more in the future we have to be aware of that".

Granted, there's no proof the current rate of change in Antarctica will continue.

"I think we should be anxious".

East Antarctica, which makes up two-thirds of the continent, is a remote region of an already remote location, where data is scarcer because there are fewer measurement stations, Koppes said.

Much of the melt-off is coming from the Pine Island and Thwaites Glaciers, victims of climate change.

Andrew Shepherd of the University of Leeds, who leads the Ice sheet Mass Balance Inter-comparison Exercise (Imbie), said it had always been suspecting changes in Earth's climate would affect the polar ice sheets. "But remember for the northern hemisphere, for North America, the fact that the location in West Antarctica is where the action is amplifies that rate of sea level rise by up to an about additional 25 percent in a city like Boston or NY". And many of those papers showed different results.

They also highlight the existential threat facing low-lying coastal cities and communities home to hundreds of millions of people.

Rising sea levels can have a unsafe impact on coastal habitats and communities as flooding increases along with higher tides and stronger storm surges. "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".