Question

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 more 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 land 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.
小題1:According to the new findings，taking steps to prevent northern forest fires may________.

A．result in a warming climate

B．cause more forest fires

C．lead to a longer fire season

D．protect the forests there

小題2:The following are the immediate effects after a forest fire EXCEPT________.

A．large amounts of greenhouse gases enter the atmosphere

B．the levels of ozone which is a type of oxygen 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

小題3:Earlier studies about northern forest fires________.

A．had analyzed all aspects of how northern fires influenced climate

B．had indicated that forest fires would pollute the atmosphere

C．had suggested that people should take measures to protect environment

D．had suggested that the fires would speed up climate warming

小題4:We can infer that forest fires in Alaska，Canada and Siberia may________.

A．warm the climate as the supposition goes

B．cool the climate by reflecting more sunlight into atmosphere

C．make more space for the growth of young trees

D．help to gain more energy rather than release more energy

Answer 1

小題1:A
小題2:C
小題3:D
小題4:B

小題1:　A
解析　細節理解題。文章第二段第一句說，為了限制溫室氣體的排放而采取措施預防北方森林大火，反而會導致北方地區氣候變暖。因此A項正確。B項和C項都是由氣候變暖引起的；D項在文中并未說明。
小題2:C
解析　細節理解題。由文章第四段前兩句可知，火災發生后，大量的溫室氣體進入大氣層，臭氧增多，灰燼落到遠方的冰山上，把冰面弄黑。這都是發生火災后會立即出現的情況。由第四段最后兩句可知，地面上的雪折射更多的太陽光返回大氣層，在第二年的春天才會發生，故選C項。
小題3:　D
解析　細節理解題。由文章第三段第二句可知D項正確。
小題4:　B
解析　推理判斷題。由文章第一段和第四段的具體分析可知，北方的森林大火能使地面上的雪向大氣折射回更多的陽光，以此達到降低氣溫的效果。