1 . Against the supposition that forest fires in Alaska, Canada and Siberia warm the climate, scientists have discovered that cooling may occur in areas where burnt trees allow more snow to mirror sunlight into space.
This finding suggests that taking steps to prevent northern forest fires to limit the release of greenhouse gases may warm the climate in northern regions. Usually large fires destroyed forests in these areas over the past decade. Scientists predict that with climate warming, fires may occur more frequently over the next several centuries as a result of a longer fire season. Sunlight taken in by the Earth tends to cause warming, while heat mirrored back into space tends to cause cooling.
This is the first study to analyze all aspects of how northern fires influence climate. Earlier studies by other scientists had suggested that fires in northern regions sped up climate warming because greenhouse gases from burning trees and plants were released into the atmosphere and thus trapped heat.
Scientists found that right after the fire, large amounts of greenhouse gases entered the atmosphere and caused warming. Ozone (臭氧) levels increased, and ashes from the fire fell on faroff sea ice, darkening the surface and causing more radiation from the sun to be taken in. The following spring, however, the landscape within the area of the fire was brighter than before the fire, because fewer trees covered the ground. Snow on the ground mirrored more sunlight back into space, leading to cooling.
“We need to find out all possible ways to reduce the growth of greenhouse gases in the atmosphere,” scientists said. They tracked the change in the amount of radiation entering and leaving the climate system as a result of the fire, and found a measurement closely related to the global air temperature. Typically, fire in northern regions occurs in the same area every 80 to 150 years. Scientists, however, found that when fire occurs more frequently, more radiation is lost from the Earth and cooling results. Specifically, they determined when fire returns 20 years earlier than predicted, 0.5 watts per square meter of area burned are soaked up by the Earth from greenhouse gases, but 0.9 watts per square meter will be sent back into space. The net effect is cooling. Watts are used to measure the rate at which energy is gained or lost from the Earth.
1. According to the new findings, efforts to prevent northern forest fires may _______.| A．lead to a longer fire season | B．be followed by more forest fires |
| C．help safeguard the forests there | D．give rise to a warming climate |
| A．large amounts of greenhouse gases enter the atmosphere |
| B．the levels of ozone increase |
| C．snow on the ground mirrors more sunlight back into space |
| D．ashes from the fire fall on the ice and darken the surface |
| A．had appealed to the public for more action to protect the environment |
| B．had suggested that the fires would speed up climate warming |
| C．had explained all aspects of how northern fires would influence the climate |
| D．had indicated that forest fires would cause pollution in the atmosphere |
| A．warm the climate as the assumption(假设) goes |
| B．make more space for the growth of young trees |
| C．help to gain more energy rather than release more energy |
| D．cool the climate by reflecting(反射) more sunlight back into atmosphere |
2 . If a diver surfaces too quickly, he may suffer the bends. Nitrogen(氮) dissolved(溶解) in his blood is suddenly liberated by the reduction of pressure. The consequence, if the bubbles (气泡)accumulate in a joint, is sharp pain and a bent body—thus the name. If the bubbles form in his lungs or his brain, the consequence can be death.
Other air-breathing animals also suffer this decompression(减压) sickness if they surface too fast: whales, for example. And so, long ago, did ichthyosaurs. That these ancient sea animals got the bends can be seen from their bones. If bubbles of nitrogen form inside the bone they can cut off its blood supply. This kills the cells in the bone, and consequently weakens it, sometimes to the point of collapse. Fossil (化石)bones that have caved in on them selves are thus a sign that the animal once had the bends.
Bruce Rothschild of the University of Kansas knew all this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past. What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years. To this end, he and his colleagues traveled the world’s natural-history museums, looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods.
When he started, he assumed that signs of the bends would be rarer in younger fossils, reflecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died, but not a single Triassic specimen(标本) showed evidence of that sort of injury.
If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, most strangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened. He suspects it was evolution in other animals that caused the change.
Whales that suffer the bends often do so because they have surfaced to escape a predator (捕食动物) such as a large shark. One of the features of Jurassic oceans was an abundance of large sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, by contrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaurs were top of the food chain. In the Jurassic and Cretaceous, they were prey(猎物) as well as predator—and often had to make a speedy exit as a result.
1. Which of the following is a typical symptom of the bends?| A．A twisted body. | B．A gradual decrease in blood supply. |
| C．A sudden release of nitrogen in blood. | D．A drop in blood pressure. |
| A．how often ichthyosaurs caught the bends | B．how ichthyosaurs adapted to decompression |
| C．why ichthyosaurs bent their bodies | D．when ichthyosaurs broke their bones |
| A．confirmed his assumption | B．speeded up his research process |
| C．disagreed with his assumption | D．changed his research objectives |
| A．failed to evolve an anti decompression means |
| B．gradually developed measures against the bends |
| C．died out because of large sharks and crocodiles |
| D．evolved an anti decompression means but soon lost it |
