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Permafrost — ground that has remained frozen for at least two years in a row — covers vast areas of the Arctic. For thousands of years, this frozen layer has acted as a giant cap, locking away huge amounts of carbon and preventing it from entering the atmosphere. However, new research warns that this natural barrier is breaking down much faster than expected.

A recent study published in the journal Earth’s Future reveals that when permafrost thaws, it becomes 25 to 100 times more permeable. In simple terms, as the ice melts, the soil turns into a sponge with wide-open holes, allowing climate-warming gases like carbon dioxide and methane(甲烷) to escape freely.

Scientists estimate that permafrost currently holds about 1,700 billion tons of carbon. That is roughly three times the amount of carbon already floating in our atmosphere today. The study, led by researchers at the University of Leeds, involved laboratory experiments that gradually warmed frozen soil samples from -18°C to +5°C. They found the most dramatic change in gas release happened when temperatures rose just above freezing — between -5°C and 1°C.

This process creates a dangerous feedback loop. As global temperatures rise, more permafrost melts. As it melts, more greenhouse gases are released, which in turn causes the planet to warm even further. “The release of huge amounts of carbon that have been stored in frozen soils is a very real danger,” said Professor Paul Glover, who led the research. “The Arctic is already warming four times faster than the rest of the world, and this could make that situation worse.”

While the findings are mainly focused on carbon and methane, researchers note there may be other hidden risks. Thawing ground could also release radon(氡), a radioactive gas linked to cancer, which might pose health threats to communities in northern regions.

The researchers stress that while these are early results, they provide clear evidence that the Arctic’s melting ice is not just a sign of climate change — it is a driver of it.

1.1. What was the main function of permafrost in the past thousands of years?

A To heat the Arctic soil.

B To store carbon underground.

C To create new ice layers.

D To speed up gas release.

解析：选B。B细节理解题。根据第一段第二句“For thousands of years, this frozen layer has acted as a giant cap, locking away huge amounts of carbon...”，可知冻土过去的主要功能是将碳封存在地下，选项B为同义转述。故选B。

2.2. The word “permeable” in Paragraph 2 is closest in meaning to ______.

A easy to pass through

B hard to break down

C likely to freeze fast

D safe to live in

解析：选A。A词义猜测题。根据第二段“the soil turns into a sponge with wide-open holes, allowing gases to escape freely”，可知融化后气体易于通过，因此“permeable”意为“可渗透的、易于通过的”。选项A “Easy to pass through”为准确释义。故选A。

3.3. What is Professor Paul Glover’s attitude towards the impact of thawing permafrost?

A Doubtful.

B Unconcerned.

C Alarmed.

D Optimistic.

解析：选C。C观点态度题。根据第四段引语“a very real danger”和“make that situation worse”，可知Paul Glover语气中透露出明确的警惕与担忧，故选项C “Alarmed”准确概括其态度。故选C。

4.4. What does the last sentence of the passage imply?

A Arctic ice melting only reflects climate change.

B Arctic ice melting actively speeds up climate change.

C Climate change will stop once the Arctic ice melts.

D Scientists have found the final cause of climate change.

解析：选B。B推理判断题。末段末句“not just a sign of climate change — it is a driver of it.”，强调北极融冰不仅是气候变化的迹象，更是其驱动者。选项B中“actively speeds up”准确转述了“driver”的含义，即融冰会主动加剧变暖。故选B。