英語聽力：自然百科 北極陷入“死亡螺旋”

According to scientists from the National Snow and Ice Data Center and NASA, Arctic sea ice appears to have reached its minimum for the year at nearly 1.7 million square miles. A chilling fact, considering that this is only about 10 % more than the lowest minimum ever, recorded in September of last year.

The levels of perennial, or year-around sea ice, have been dropping rapidly. According to NASA, the drop in ice levels has averaged nearly 10% each decade since NASA began satellite imaging in 1979.

Between the winters of 2005 and 2007, the amount of perennial ice that was lost was equivalent to an area the size of Texas and California combined. While perennial sea ice used to cover up to 60% of the Arctic, it now only covers about 30%.

Perennial sea ice is the thick ice that remains solid throughout the year and provides important habitat and hunting grounds for polar bears, while the surrounding seasonal ice melts and reforms each year. This data further reinforces previous evidence that the minimum level of perennial sea ice in the Arctic is dropping nearly every year.

An Arctic climate expert at the National Snow and Ice Data Center tells National Geographic News the ice is in a death spiral. Mark Sered says Arctic summer ice could be completely lost by the year 2030. The drop-off in sea ice can have global ramifications both on land and in the water.

Sea ice works as a mirror, reflecting the Sun's rays. The more sea ice that exists, the more the Sun's rays are reflected off the Earth’s surface. But when sea ice levels decline, more of the Sun's rays can be absorbed by the seas and by land. This can then lead to a rise in global temperatures and disrupt the fragile equilibrium of the world's climate. Worse yet, this can result in what scientist called, ice-albedo feedback, meaning the more the sea ice declines, the more likely it will continue to decline.