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Scientists have warned that Greenland will be ice-free in the next thousand years unless greenhouse gas emissions are substantially reduced. Using three different climate change scenarios, a team of researchers tested how the ice would respond in the future. Their findings showed that if we continue warming the earth, 100 percent of Greenland's present-day ice mass will be gone. This could raise sea levels by over seven meters (23 feet).

The Greenland Ice Sheet is a huge mass, almost the size of Alaska—but it has started to disintegrate. Ocean temperatures along its west coast rose by 1.5 ℃ between 1996 and 1998, causing the ice sheet to retreat and thin. Scientists are worried that warming could cause it to collapse—an event predicted to raise sea levels so much that it would submerge a number of major U.S. cities, including San Francisco, Los Angeles and New Orleans.

Scientists are working to understand how Greenland's ice sheet will respond to future warming. The Intergovernmental Panel for Climate Change (IPCC) estimates that if global greenhouse gas emissions continue, global temperatures will increase by between 2.6 ℃ and 4.8 ℃. If emissions are reduced drastically, this can be reduced to between 0.3 ℃ and 1.7 ℃. A third scenario is emissions peaking at the middle of the century than drop rapidly—if this happens warming of between 1.1 ℃ and 2.6 ℃.

Using these three climate change scenarios, researchers developed a model for how Greenland will respond to warming and ran 500 computer simulations to show what could happen over the next 1,000 years. The model took into account atmospheric and ocean conditions as well as ice geometry, flow and thickness.

Their findings, published in Science Advances, showed that “in a thousand years the Greenland Ice Sheet will look significantly different than today”. Under the best case scenario, Greenland will lose between 8 and 25 percent of its present-day mass. Under moderate climate change it would lose between 26 and 57 percent, while under the worst case scenario, between 72 and 100 percent will disappear.

1.What would make the Greenland ice-free?

A The greenhouse gas emission.

B The rising sea level.

C The large number of ice mass.

D The changing scenarios.

解析：选A。细节理解题。根据文章第一段第一句unless greenhouse gas emissions are substantially reduced可以得知温室气体排放会导致格陵兰岛上的冰消失，故选A。

2.The underlined word “disintegrate” in the second paragraph may mean “_______”.

A rise

B collapse

C drown

D retreat

解析：选B。词义猜测题。根据文章第二段第三句Scientists are worried that warming could cause it to collapse可以得知格陵兰岛的冰盖开始“坍塌”，disintegrate与collapse同义，故选B。

3.What will happen if greenhouse gas emissions are reduced sharply?

A Global temperatures will not rise at all.

B Global temperatures will not rise than 2 ℃.

C Global temperatures will get to its peak.

D Global temperatures will drop rapidly.

解析：选B。细节理解题。根据第三段第三句If emissions are reduced drastically, this can be reduced to between 0.3 ℃ and 1.7 ℃.可以得知如果排放急剧减少，气温将升高不超过2℃，故选B。

4.What would happen to Greenland under the worst case scenario?

A It would lose between 8 and 25 percent of its present-day mass.

B It would lose between 26 and 57 percent of its present-day mass.

C Between 72 and 100 percent of its present-day mass would disappear.

D Its present-day mass would not changed rapidly.

解析：选C。细节理解题。根据文章最后一段最后一句Under moderate climate change it would lose between 26 and 57 percent, while under the worst case scenario, between 72 and 100 percent will disappear.可以得知在最坏的情况下，格陵兰岛72%到100%的冰块会消失，故选C。