2020수능특강 영어 21강 본문

 

21강

1

One possible disaster resulting from warmer temperatures in northern areas is a potential tipping point associated with the Greenland ice sheet. The “Atlantic conveyor belt” consists of warm water moving up the eastern coast of North America as the Gulf Stream and then sinking 10,000 feet near Greenland and moving back to the equator, where it warms and rises again. Large amounts of freshwater entering the North Atlantic off Greenland as the ice melts could shut down the conveyor belt because freshwater does not sink like saltwater. This could trigger an ice age in North America and Europe—an ironic consequence of global warming but one associated in the past with the conveyor‑belt shutdown. Climate scientists worried about this possibility several decades ago and then decided about a decade ago that it was very unlikely, but they have now begun to worry about it again.

 

2

Dams affect keystone species. First they block the migration of salmon upstream to their spawning streams. Scientists have created fish ladders as well as management schemes that transport the fish around the obstacles, but these efforts have limited success. As salmon are separated from the ecological functions of a habitat, other keystone species are impacted. In this example, one such keystone species would be the grizzly bear. Without a large amount of salmon, grizzly bears cannot transport the amount of oceanic nutrients inland to help enrich soils for trees. Lack of vegetation cover then affects songbirds and small mammals. If these species disappear, the animals that hunt them disappear. Rivers that do not produce a bonanza of salmon will not attract bears. They migrate to other areas entirely, creating a gap at the center of the ecological arch.

 

3

Sixty‑five million years ago a meteor the size of New York slammed into the Earth. The environmental chaos that ensued is widely believed to have put paid to the dinosaurs. But it also had a less well‑known effect. According to Ken Caldeira at the Carnegie Institution of Washington in California, the meteor also threw up vast amounts of sulfur, which then rained down on the ocean as sulfuric acid. The upper ocean became acidified for a brief moment, perhaps only one or two years. But that was enough. More or less every sea creature that built shells or skeletons out of calcium carbonate became either rare or extinct. A handful of corals must have survived, or we would not still have them on Earth today. But they were nonetheless too scarce to leave their imprint; they did not reappear in the fossil record for a full two million years.

 

4

It is not common for both sides of a noise barrier to look identical because it is usually only one side of the barrier that is required to reflect or absorb noise. The difference between the two sides of a barrier should be determined on aesthetic as well as acoustic grounds: each side of the barrier should be designed to integrate with the landscape character and the backdrop against which it is to be viewed. Thus, the face of the barrier that may be facing a road corridor may include a pattern or have a bright colour, whereas the other face, which could stand opposite housing, may be treated in a more discreet fashion. Here, the façade may be plain and designed to merge in with neighbouring planting. Most barrier types can be designed with this in mind with the obvious exceptions of transparent barriers and many bio‑barriers. Planting on either side of the barrier should also be designed with each separate identity in mind.