The rise in sea levels seen over the past century is unmatched by any period in the past 6,000 years, according to a long-lasting analysis of historical sea level trends.

The reconstruction（再现）of 35,000 years of sea level fluctuations（变动）finds that there is no evidence that levels changed by more than 20cm in a relatively steady period that lasted between 6,000 years ago and about 150 years ago.

This makes the past century extremely unusual in the historical record, with about a 20cm rise in global sea levels since the start of the 20th century. Scientists have noted rising temperatures, which have caused polar ice to melt and thermal expansion of the sea, as a primary cause of the sea level increase.

The 35,000-year span of the study was chosen as this consists of an interglacial period. Researchers could pick submerged sediments（沉淀物）that may include tree roots, suggesting a previously lower sea level.

Ice started melting about 16,000 years ago, with this melting ending about 8,000 years ago. A slowdown in sea level changes didn’t occur until 6,000 years ago, however.

“It’s like if you leave a big block of ice on the table, it doesn’t melt immediately, there’s always a delay in the system,” said Kurt Lambeck, who led the research. “We know from the last interglacial period that when temperatures were several degrees warmer than today there was a lot more water in the oceans, with levels around 4 to 5m higher than today. The question is how fast that change occurs when you increase temperatures.”

Lambeck said the sea level increase of the past 100 years is “beyond dispute”, backed up by separate data from salt flats and also changes to the sea floor caused by the extra weight of water.

 “All the studies show that you can’t just switch off this process. Sea levels will continue to rise for some centuries to come even if we keep carbon emissions at present day levels,” he said.

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1.What makes the 20th century unusual in the historical record?

A Polar ice started to melt and affect seal level.

B Rise of temperatures led to expansion of the sea.

C Sea level started to slow down.

D The largest sea level increase took place.

解析：选D。D 细节理解题。根据文章第三段This makes the past century extremely unusual in the historical record可知，在过去的一个多世纪里，海平面上升幅度很大，创下6,000年来海平面上涨的纪录。

2.What is likely to cause the sea level to increase?

A Tree roots that sank into the bottom of the ocean.

B The rise of temperatures caused polar ice melting.

C Salt flats formed by sea water.

D Carbon emission caused by modern industry.

解析：选B。B 细节理解题。根据文章第三段…rising temperatures, which have caused polar ice to melt … as a primary cause of the sea level increase可知，温度升高引起极地冰融化，从而使海平面升高。

3.What can be implied in the passage?D. Sea level started to rise from 6,000 years ago.

A Sea levels will be higher in future than it is today.

B Sea levels will fall with carbon emissions reduced.

C Scientists have studied sea level changes for thousands of years.

D Sea level started to rise from 6,000 years ago.

解析：选A。A 推理判断题。根据文章最后一段Sea levels will continue to rise for some centuries to come可以判断，未来的海平面甚至比现在还要高。

4.Why is the sea level increase in the last century beyond question?

A Sediments of tree roots have been found at the bottom of sea.

B There was data of ice melting which caused sea level to rise.

C Sea floor changed as a result of water level keeping rising.

D In the last century temperatures were several degrees warmer than today.

解析：选C。C 细节理解题。根据文章第七段…“beyond dispute”, backed up by …and also changes to the sea floor caused by the extra weight of water可知，由于海洋水量增加，水体重量的压迫使得海底出现变化。这些都是海平面上升的有力证据。

5.Which column of a newspaper does this passage belong to?

A Technology.

B Environment.

C Lifestyle.

D History.

解析：选B。B 推理判断题。这是一篇海洋环境的研究报告，属于环境主题，因此选B。