A Melting Point

Since the 1970s the Arctic has been the main cause of rising sea levels around the world. Over two-thirds of the Arctic’s contribution comes from ice loss from Greenland, according to the latest SWIPA report. 【小题1】

The interaction between outlet glaciers (冰山) and ice streams as they flow—ever faster—into the Arctic ocean, how pressurised meltwater combines with soft sediments (沉淀物) to lubricate (润滑) the bed of Greenland’s ice sheet, and the impact of increased darkening across the ice sheet’s surface are all poorly understood, says Alun Hubbard from the University of Tromso.

Understanding what is going on will be tough. Fieldwork on Greenland’s remote ice sheet is expensive. 【小题2】Even if current emissions remain stable, what is agreed upon is that global sea levels will rise by 74 cm by the end of the century. Vast coastal cities such as Rotterdam, New York and Mumbai will suffer.

Floods of icy meltwater will change the weather, too. By altering the salinity(盐度)and temperature of different parts of the sea, circulation patterns both within the Arctic ocean and,   consequently, in the atmosphere will change. That will affect weather and climate phenomena, such as India’s monsoon season, thousands of miles to the south. 【小题3】Where they differ is on just how large the effect will be and which processes are involved.

【小题4】Changes to wind patterns can bring cooler weather farther south, which could help explain extremely cold conditions in north-eastern America in recent winters. But these wind shifts have to be large enough to cancel out more general background warming caused by the loss of sea ice, says James Screen of the University of Exeter. “In north-west Europe, it seems that these two effects of melting sea ice roughly balance out,” he says. But climatic imbalances from Arctic melting could prove far more harmful elsewhere in the world.