【推荐2】Polar bears normally need sea ice to hunt seals, but an isolated (孤立的) group of polar bears living on the mountainous coast of southeast Greenland have figured out how to make a living, even though the sea ice there melts away early in the year.

These bears have found a way to supplement (补充) their limited sea ice supply by hunting on freshwater ice that comes from glaciers on land. The glacial ice falls off in pieces into fjords (峡湾), where the pieces get together into a floating platform that the polar bears use to catch seals, according to a report in the journal Science.

Climate change is making sea ice less and less. “Loss of sea ice is the primary threat to polar bears,” says Kristin Laidre of the University of Washington, lead author of the new study. But, she says, this new work suggests some bears might be able to deal with a decreased amount of sea ice - at least for a while - in places like Greenland where they can take advantage of floating glacier ice.

While local people have long known that bears live in southeast Greenland, it’s a remote, challenging environment that’s not frequented by humans. “It’s a coastline with huge mountain peaks, lots of winds, extreme conditions and plenty of fogs.” says Laidre, who has spent years working with colleagues to survey polar bears living on Greenland’s 1,800-mile-long east coast.

To see what they could find in southeast Greenland, the team had to take helicopters from the nearest settlement and fly for two hours in a straight line to the coast. “We arrived in these fjords, very isolated fjords, and there’s essentially no sea ice or very poor sea ice offshore,” says Laidre, explaining that the researchers expected to find few bears. “But there were a lot of bears in these fjords,” she says. “It was clearly just a unique habitat.”

The sea ice continues to exist in these fjords for only around a hundred days a year, she notes, meaning that bears don’t have much time to use it as a hunting ground.

【推荐3】Corn is the most dominant agricultural product in the U.S., and perhaps the world.     1     But when their crops failed, the settlers of the New World decide to mix corn into their agricultural efforts. Fast-forward a couple of hundred years, and this tall grass now covers 90 million acres of land in America alone and accounts for some 10% of total crop production globally.

    2     One is that growing corn generates far more calories per unit of land than nearly any other crop. Another key factor was that much more ammonium nitrate (硝酸铵), a kind of explosive, was left after World War Ⅱ. Agriculture scientists successfully repurposed it into a cheap form of fertilizer. This allowed corn to be grown in the same fields year after year, without reducing the nitrogen in the soil.     3     We can eat it, process it into syrup, fuel our cars with it and feed it to our animals.

The dominance of corn, however, has negative effect. Currently, we use approximately 40% of corn grown in the U.S. to create ethanol (乙醇) and 36% to feed animals.     4     Ethanol has a low “energy-returned-on-energy-invested” ratio (比率), meaning we must put a large amount of energy into producing it. An indirect negative effect of the dominance of corn has been its help in fueling explosive growth in the livestock industry.

    5     Traditional monoculture farming, which means growing one type of crop continuously, worsens soil and often leads to harmful runoff into streams and rivers. Farmers themselves can change from monoculture practices to those that include a wider variety of species. As consumers, we can buy organic corn. Though not absolutely eco-friendly, organic agriculture is miles ahead of traditional farming.