托福阅读真题+题目+答案：Volcanoes and Climate Change

托福阅读真题+题目+答案：Volcanoes and Climate Change

Mount Tambora dominates the small Indonesian island of Sumbawa in the Flores Sea east of Java. In 1815 it exploded in the largest eruption in the last 20,000 years, ejecting between 125 and 175 cubic kilometers of pumice(a type of rock formed by volcanoes)and ash. The year after the eruption, 1816, would become known as the year without a summer. " Climate is influenced by many processes operating simultaneously, so the precise effect of Tambora is not easily gauged. The eruption was coincident with a span of several decades, from about 1790 to 1830, of colder climate apparently caused by a considerable decrease in solar activity. The years 1812 to 1818 were among the coldest of these, and this may have been primarily a result of the change in solar activity. It is also possible that the other large eruptions that occurred in that decade-soufriere Hills(Montserrat, 1812), Mayon(Philippines, 1814), Colima(Mexico, 1814). and Beerenberg(North Atlantic, 1818)contributed to the cold conditions. Sparseness of climate records adds to this uncertainty. Much of our knowledge comes from tree rings and other natural recorders of time and climate.

1.The word “simultaneously” in the passage is closest in meaning to

A.periodically

B.frequently

C.in similar ways

D.at the same time

2.In paragraph 1, why does the author discuss levels of solar activity?

A.To argue that decreased levels of solar activity may lead to increased volcanic activity on Earth

B.To explain how tree rings function as natural recorders of time and climate

C.To provide an example of a theory about climate change that has been proven incorrect

D.To provide an additional explanation for the period of cold that followed the Tambora eruption

How, exactly, do volcanic eruptions modify climate? Until recently, it was thought that dust in the form of particles of volcanic ash simply blocked incoming sunlight, and thus that the explosiveness of an eruption and the amount of solid material blown into the atmosphere were important parameters .We now know however that the effects of dust are negligible because it simply does not remain in the atmosphere long enough to block sunlight. Far more important is the amount of sulfur dioxide injected into the stratosphere, the base of which is about 10 to 15 kilometers high. In the atmosphere, sulfur dioxide reacts rapidly with water vapor to form sulfuric acid. Sulfuric acid forms an aerosol. a cloud of submicroscopic droplets less than a ten-thousandth of a millimeter in diameter-small enough that the droplets do not rapidly settle. In contrast, in the troposphere, which extends from the stratosphere to Earth's surface, precipitation rapidly washes out sulfuric acid and other pollutants. (This cannot happen in the stratosphere because it is above the clouds. ) The aerosol in the stratosphere absorbs some solar radiation, thereby causing cooling of the troposphere. Fortunately for life, the aerosol remains in the stratosphere for only a few years, so the effect of cataclysmic eruptions on climate is temporary.

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