Temperatures at Hudson Bay have risen by one half degree Fahrenheit every decade since 1950. Winter ice on the bay melts three weeks earlier than it did just 25 years ago, which means three fewer weeks of polar bear mealtime. Result: Polar bears are 10 percent thinner and produce 10 percent fewer cubs than they did 20 years ago. And though climatologists hotly debate the causes behind Earth's Arctic meltdown, "these changes are startling and unexpected," says James McCarthy, co-leader of the United Nations Intergovernmental Panel on Climate Change.
The plight of polar bears is just the tip to the iceberg when it comes to mounting evidence of global warming. "There's definitely a stark contrast with the way things were at the start of the 20th century," says atmospheric scientist Leonard Druyan, of Columbia University. Recent data show the volume of Arctic sea ice has shrunk 20 percent since the 1950s; glaciers around the world are melting at rapidly increasing rates. Rivers and lakes in North America, Asia, and Europe now freeze about nine days later and thaw 10 days earlier than they did a century ago.
Most scientists believe the only effective strategy to halt global warming is to drastically reduce emissions of powerful air pollutants like carbon dioxide, which accounts for two-thirds of all greenhouse gases. In the last 150 years, the surging use of fossil fuels—coal, oil, and natural gas—has released 270 billion tons of carbon into the air in the form. of carbon dioxide. Fortunately, oceans, plants, and soils absorb more than half of all atmospheric carbon dioxide—without them world temperatures might have already soared at an alarming rate.
By saying "Spring is usually prime food time for 1,200 polar bears"(Line 1, Para. 1), the author means that ______.
A.spring is usually a good time for polar bears to carry out their mating rituals
B.the polar bears usually eat a lot in the spring
C.spring is generally a good time to hunt polar bears
D.polar bears usually hibernate in the spring
第6题
A、等高线密集,则等高线平距较小,地面坡度较大,地形陡峭
B、等高线密集,则等高距较小,地面坡度较小,地形陡峭
C、等高线稀疏,则等高线平距较大,地面坡度较小,地形平坦
D、等高线稀疏,则等高距较大,地面坡度较小,地形平坦
第7题
地形图上相邻等高线间的水平距离,称为等高线平距。在同一幅图上,等高线平距越大,地面坡度()
A.越大
B.不变
C.越小
D.两者没有关系
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