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“Usually when we walk through the rainforest, we hear a soft sound from all the moist leaves and organic debris on the forest floor,” says ecologist Daniel Nepstad. “Nowwe increasingly get rustle and crunch. That’s the sound of a dying forest. ”
Predictions of the collapse of the tropical rain forests have been around for years. Yet until recently the worst forecasts were almost exclusively linked to direct human activity, such as clear-cutting and burning for pastures or farms. Left alone, it was assumed, the world’s rain forests would not only flourish but might even rescue us from disasters by absorbing the excess carbon dioxide and other planet-warming greenhouse gases. Now it turns out that maybe wishful thinking. Some scientists believe that the rise in carbon levels means that the Amazon and other rain forests in Asia and Africa may go from being assets in the battle against rising temperatures to liabilities. Amazon plants, for instance, hold more than 100billionmetric tons of carbon, equal to 15-years of tailpipe and chimney emissions. If the collapse of the rain forests speeds up dramatically, it could eventually release 3.5 — 5billionmetric tons of carbon in to the atmosphere each year, making forests the leading source of greenhouse gases.
Uncommonly severe droughts brought on by global climate change have led to forest-eating wildfires from Australia to Indonesia, but now here more acutely than in the Amazon. Some experts say that the rainforest is already at the brink of collapse.
Extreme weather and reckless development are plotting against the rainforest in ways that scientists have never seen. Trees need more water as temperatures rise, but the prolonged droughts have robbed them of moisture, making whole forests easily cleared of trees and turned into farmland. The picture worsens with each round of El Nino, the unusually warm currents in the Pacific Ocean that drive up temperatures and invariably presage droughts and fires in the rainforest. Runaway fires pour even more carbon into the air, which increases temperatures, starting the whole vicious cycle all over again.
More than paradise lost, a perishing rainforest could trigger a domino effect sending winds and rains kilometers off course and loading the skies with even greater levels of greenhouse gases — that will be felt far beyond the Amazon basin. Ina sense, we are already getting a glimpse of what’s to come. Each burning season in the Amazon, fires deliberately set by frontier settlers and developers hurl up almost half a billion metric tons of carbon a year, placing Brazil among the top five contributors to greenhouse gases in the world.
53. The author argues that the rising carbon levels in rain forests may______.
A.Turn them into a major source of greenhouse gases
B.change the weather patterns throughout the world leaves
C.pose a threat to wildlife
D.accelerate their collapse
54. What has made it easier to turn some rain forests into farmland?
A.Rapid rise in carbon levels.
B.Reckless land development.
C.Lack of rainfall resulting from global warming.
D.The unusual warm currents in the Pacific Ocean.
55. What makes Brazil one of the world’s top five contributors to greenhouse gases?
A.The domino effect triggered by the perishing rain forests.
B. Its practice of burning forests for settlement and development.
C. The changed patterns of winds and rains in the Amazon area.
D.Its inability to curb the carbon emissions from industries.
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