There have been claims that warming on Mars and Pluto is proof that the recent warming on Earth is caused by an increase in solar activity, and not by greenhouse gases. But we can say with certainty that, even if Mars, Pluto or any other planet has warmed in recent years, it is not due to changes in solar activity.
The Sun's energy output has not increased since direct measurements began in 1978. If increased solar output really was responsible, we should be seeing warming on all the planets and their moons, not just Mars and Pluto.
Our solar system has eight planets, three dwarf planets and quite a few moons with at least a thin atmosphere, and thus a climate of sorts. Their climates will be affected by local factors such as orbital variations, changes in reflectance and even volcanic eruptions, so it would not be surprising if several planets and moons turn out to be warming at any one time.
One theory is that winds have recently swept some areas of Mars clean of dust, darkening the surface, warming the Red Planet and leading to further increases in windiness—a positive feedback effect.
Observations of the thickness of Pluto's atmosphere in 2002 suggested the dwarf planet was warming even as its orbit took it further from the Sun. The finding confused astronomers at the time, and the cause had yet to be determined.
It has since been suggested that this is due to a greenhouse effect: As it gets closer to the Sun, Pluto may warm enough for some of the methane ice on its surface to turn into a gas. This would cause further warming, which would continue for a while even after Pluto's orbit starts to take it away from the Sun.
本文是一篇科普说明文，有人认为地球变暖是因为太阳活动而不是温室气体，文章驳斥了这个观点。同时对太阳系里另外一些星星的变暖情况分别进行了分析。
1．What cause(s)the warming of some planets?
A．The solar system. B．Their local factors.
C．Volcanic mountains. D．The thin atmosphere.
答案：B
解析：细节理解题。根据第三段第二句Their climates will be affected by local factors such as orbital variations, changes in reflectance and even volcanic eruptions可知，导致某些星球变暖的原因很多，可能是受到这些星球的当地因素的影响。故B项正确。
2．What is the outcome of the recent winds on Mars?
A．They've cooled the planet.
B．They've left a clear sky.
C．They've caused more winds.
D．They've helped clean the planet.
答案：C
解析：推理判断题。根据文章第四段One theory is that winds have recently swept some areas of Mars clean of dust, darkening the surface, warming the Red Planet and leading to further increases in windiness—a positive feedback effect.可知，火星上的风吹走了灰尘，让火星变暖同时也会导致风力的进一步变大。故C项正确。
3．What do we know about the thickness of Pluto's atmosphere?
A．It remains mysterious.
B．It troubled astronauts.
C．It has become thinner.
D．It contributes to the warming.
答案：D
解析：细节理解题。根据第五段第一句Observations of the thickness of Pluto's atmosphere in 2002 suggested the dwarf planet was warming even as its orbit took it further from the Sun.可知，冥王星厚厚的大气层导致了冥王星变暖。故D项正确。
4．Which of the following might lead to the warming on Earth according to the writer?
A．Solar activity.
B．Mars and Pluto.
C．Greenhouse gases.
D．The Sun's energy output.
答案：C
解析：推理判断题。根据文章第一段第一句可知有人认为地球变暖是因为太阳活动而不是温室气体。根据第二句But we can say with certainty that, even if Mars, Pluto or any other planet has warmed in recent years, it is not due to changes in solar activity.可知，我们可以确切地说地球变暖不是因为太阳运动，也就是说地球变暖是由温室气体导致的。故C项正确。
