Antarctic meltwater lakes threaten sea levels: study

Marlowe HOOD –
Antarctic meltwater lakes are far more common than once thought and could destabilise glaciers, potentially lifting sea levels by metres as global warming sets in, scientists said on Wednesday.
Most vulnerable are the massive, floating ice shelves that ring the Antarctic continent and help prevent inland glaciers from sliding towards the sea, they reported in the journal Nature.
Antarctica holds enough frozen water to push up global oceans by tens of metres. Meltwater pooling on the surface of ice shelves can suddenly drain below the surface, fracturing the ice with heat and pressure, studies have shown.
“This is widespread now, and has been going on for decades,” said lead author Jonathan Kingslake, a glaciologist at Columbia University’s Lamont-Doherty Earth Observatory.
To piece together a “big picture”, Kingslake and his team combed through thousands of photos taken from military aircraft starting in 1947, along with satellite images dating back to 1973.
They catalogued nearly 700 distinct networks of interconnected ponds, channels and streams criss-crossing the continent.
A few reached to within 600 kilometres (375 miles) of the South Pole at altitudes topping 1,300 metres (4,300 feet), where liquid water was assumed to be rare or nonexistent.
Rising temperatures are eroding ice shelves — which can be hundreds of metres thick and extend hundreds of kilometres over ocean water — on two fronts, scientists say. From above, warmer air and shifting winds remove snow cover, exposing the bedrock ice underneath.
Because ice has a darker, blueish tint, it absorbs more of the Sun’s radiation rather than reflecting it back into space.
But the main damage to ice shelves comes from ocean water eroding their underbellies.
Normally, that erosion is compensated by the accumulation of fresh snow and ice from above.
But oceans in recent decades have absorbed much of the excess heat generated by global warming, which has lifted average global air temperatures by one degree Celsius (1.8 degrees Fahrenheit) since the mid-19th century. — AFP