Global Warming

How Much Ice Can Antarctica Afford to Lose?

Over the past 20 years, ice shelves in Antarctica that normally support the rest of the continent's glaciers have been shrinking, and some have disappeared entirely. How much more ice can disintegrate before Antarctic glaciers start freely tumbling into the ocean?

A recent study led by researchers at the Friedrich-Alexander-Universität, in Germany, has mapped out which Antarctic ice shelves are buttressing the most ice and which are more "passive" and thus can stand to lose a large area without any immediate effect on the rest of the ice shelf.

Ice shelves are slabs of ice several hundred meters thick that extend from the edges of the mainland and float on the surface of the sea. They are firmly linked to glaciers and ice streams in mainland Antarctica, which slowly push the floating ice farther seaward, according to the researchers. When the seaward fronts of these ice shelves break off, they form new icebergs and the loss of ice is naturally replenished by the glacier ice from the mainland flowing in.

Some of the ice shelves, however, also push back on the glaciers, providing resistance and reducing the speed at which the glaciers flow into the ocean, said lead study author Johannes Fürst, a research assistant at the Institute of Geography at the Friedrich-Alexander-Universität.

"Ice shelves restrain the outflow from upstream like a plug in a bathtub," Fürst told Live Science. "If you take the plug out, the water runs out, except this is frozen water and if you take out the ice shelves its flow will accelerate out into the ocean and eventually raise sea levels."

In 1995, Antarctica's Larsen A ice shelf collapsed, removing ice cover from an area equivalent to the size of Berlin, according to Fürst. Seven years later, the much larger Larsen B ice shelf also broke apart. While the disintegration of the two shelves did not have an immediate effect on sea levels, the ice loss resulted in upstream glaciers accelerating by up to eight times their normal flow, according to the researchers.

Overall, the researchers found that 13 percent of the continent's ice shelf area can be classified as passive — an area about twice the size of Spain. This includes the Larsen C ice shelf in the Weddell Sea, which the researchers found is almost entirely a passive ice shelf.

Ice shelves in the Amundsen and Bellingshausen seas, however, are the most susceptible to further ice loss, according to the research findings. They are made up of 7 percent and 5 percent passive ice, respectively, the researchers found.

Global Warming

Record Melt Occurring in Greenland Glaciers

Greenland’s glaciers are retreating under the influence of climate change at least twice as fast as any other time in the past 9,500 years, according to new research.

Scientists from Columbia University’s Earth Institute made the discovery after examining sediment cores from the bottom of a glacier-fed lake in southeastern Greenland.

They then compared the findings to analyses of similar cores from Iceland and Canada's Baffin Island, and with recent satellite observations.

They found that before the 20th century, the fastest rate of glacier retreat occurred about 8,500 years ago, when the Earth's position relative to the sun resulted in more summer sunlight warming the Arctic.

Despite less direct summer sunlight in recent years, Greenland’s glaciers have melted at an unprecedented rate because of warming brought on by higher greenhouse gas concentrations.

“If we compare the rate that these glaciers have retreated in the last hundred years to the rate that they retreated when they disappeared between 8,000 and 7,000 years ago, we see the rate of retreat in the last 100 years was about twice what it was under this naturally forced disappearance,” said study co-author William D’Andrea.

The study also provided new evidence for just how sensitive glaciers are to temperature, showing that they responded to past abrupt cooling and warming periods, some of which might have lasted only decades.

Global Warming

Central Asian glaciers shrinking fast

Central Asian glaciers have melted at four times the global average since the early 1960s, shedding 27 per cent of their mass, according to a study released today.

By 2050, warmer temperatures driven by climate change could wipe out half the remaining glacier ice in the Tien Shan mountain range, reported the study, published in Nature Geoscience.

At stake is a critical source of water for people in Kazakhstan, Kyrgyzstan and Uzbekistan, as well as a section of northwest China.

“Glaciers are actually huge water stores. They can balance water between wet and dry years,” said co-author Doris Duethmann, a researcher at the GFZ German Research Centre for Geosciences in Potsdam.

Tien Shan glaciers have lost an average of 5.4 billion tonnes of ice per year since the 1960s, totalling some 3,000 square kilometres (1,158 square miles).

The rate at which the glaciers shrank greatly accelerated in the 1970s and 1980s.

Climate models point to higher summer temperatures in coming decades along the 2,500 kilometres of the Tien Shan range, thus making the glaciers even more vulnerable, the study said.

Environment

Many of the world’s glaciers and ice sheets are retreating in the face of global warming, but a few are stable or growing — including glaciers in the western Himalaya Mountains, according to a new report. The mountains in the region form the headwaters of several major river systems — including the Ganges, Mekong, Yangtze, and Yellow rivers — which serve as sources of drinking water and irrigation supplies for about 1.5 billion people.

The US National Weather Service in Los Angeles released two notices of triple-digit record-breaking temperatures in Long Beach over the weekend. On Friday, a high of 104 degrees was recorded, breaking the old record of 96 set in 1979.

Global Warming

A  recent study suggests that Greenland's glaciers may be melting at a slower rate leading to a slower rise in sea water levels. The study extended over ten years ending in 2011. A caveat is that the full effects of global warming may not have reached Greenland's  northern glaciers yet.