Long after the lava has cooled, the effects of a
major volcanic eruption may linger on. In the
atmosphere a veil of fine dust and sulfuric acid droplets
can spread around the globe and persist for years.
(5) Researchers have generally thought that this veil can
block enough sunlight to have a chilling influence on
Earth’s climate. Many blame the cataclysmic eruption
of the Indonesian volcano Tambora in 1815 for the
ensuing “year without a summer” of 1816—when parts
(10) of the northeastern United States and southeastern
Canada were hit by snowstorms in June and frosts in
August.

The volcano-climate connection seems plausible,
but, say scientists Clifford Mass and Davit Portman, it
(15) is not as strong as previously believed. Mass and
Portman analyzed global temperature data for the years
before and after nine volcanic eruptions, from Krakatau
in 1883 to El Chichón in 1982. In the process they tried
to filter out temperature changes caused by the cyclic
(20) weather phenomenon known as the El Niño-Southern
Oscillation, which warms the sea surface in the
equatorial Pacific and thereby warms the atmosphere.
Such warming can mask the cooling brought about by
an eruption, but it can also mimic volcanic cooling if
(25) the volcano happens to erupt just as an El Niño
induced warm period is beginning to fade.
Once El Niño effects had been subtracted from the
data, the actual effects of the eruptions came through
more clearly. Contrary to what earlier studies had
(30) suggested, Mass and Portman found that minor
eruptions have no discernible effect on temperature.
And major, dust-spitting explosions, such as Krakatau
or El Chichón, cause a smaller drop than expected in
the average temperature in the hemisphere (Northern or
(35) Southern) of the eruption—only half a degree
centigrade or less—a correspondingly smaller
drop in the opposite hemisphere.

Other researchers, however, have argued that even
a small temperature drop could result in a significant
(40) regional fluctuation in climate if its effects were
amplified by climatic feedback loops. For example, a
small temperature drop in the northeastern U.S. and
southeastern Canada in early spring might delay the
melting of snow, and the unmelted snow would
(45) continue to reflect sunlight away from the surface,
amplifying the cooling. The cool air over the region
could, in turn, affect the jet stream. The jet stream
tends to flow at the boundary between cool northern air
and warm southern air, drawing its power from the
(50) sharp temperature contrast and the consequent
difference in pressure. An unusual cooling in the region
could cause the stream to wander farther south than
normal, allowing more polar air to come in behind it
and deepen the region’s cold snap. Through such a
(55) series of feedbacks a small temperature drop could be
blown up into a year without a summer.

1. Which one of the following most accurately expresses the main idea of the passage?

(A) The effect of volcanic eruptions on regional temperature is greater than it was once thought to be.
(B) The effect of volcanic eruptions on regional temperature is smaller than the effect of volcanic eruptions on global temperature.
(C) The effect of volcanic eruptions on global temperature appears to be greater than was previously supposed.
(D) Volcanic eruptions appear not to have the significant effect on global temperature they were once thought to have but might have a significant effect on regional temperature.
(E) Researchers tended to overestimate the influence of volcanic eruptions on global temperature because they exaggerated the effect of cyclical weather phenomena in making their calculations.


2. Not taking the effects of El Niño into account when figuring the effect of volcanic eruptions on Earth’s climate is most closely analogous to not taking into account the

(A) weight of a package as a whole when determining the weight of its contents apart from the packing material
(B) monetary value of the coins in a pile when counting the number of coins in the pile
(C) magnification of a lens when determining the shape of an object seen through the lens
(D) number of false crime reports in a city when figuring the average annual number of crimes committed in that city
(E) ages of new immigrants to a country before attributing a change in the average of the country’s population to a change in the number of births


3. The passage indicates that each of the following can be an effect of the El Niño phenomenon EXCEPT:

(A) making the cooling effect of a volcanic eruption appear to be more pronounced than it actually is
(B) making the cooling effect of a volcanic eruption appear to be less pronounced than it actually is
(C) increasing atmospheric temperature through cyclic warming of equatorial waters
(D) initiating a feedback loop that masks cooling brought about by an eruption
(E) confounding the evidence for a volcano climate connection


4. Which one of the following most accurately characterizes what the author of the passage means by a “minor” volcanic eruption (line 30)?

(A) an eruption that produces less lava than either Krakatau or El Chichón did
(B) an eruption that has less of an effect on global temperature than either Krakatau or El Chichón did
(C) an eruption whose effect on regional temperature can be masked by conditions in the hemisphere of the eruption
(D) an eruption that introduces a relatively small amount of debris into the atmosphere
(E) an eruption that causes average temperature in the hemisphere of the eruption to drop by less than half a degree centigrade


5. To which one of the following situations would the concept of a feedback loop, as it is employed in the passage, be most accurately applied?

(A) An increase in the amount of decaying matter in the soil increases the amount of nutrients in the soil, which increases the number of plants, which further increases the amount of decaying matter in the soil.
(B) An increase in the number of wolves in an area decreases the number of deer, which decreases the grazing of shrubs, which increases the amount of food available for other animals, which increases the number of other animals in the area.
(C) An increase in the amount of rain in an area increases the deterioration of the forest floor, which makes it harder for wolves to prey on deer, which increases the number of deer, which gives wolves more opportunities to prey upon deer.
(D) An increase in the amount of sunlight on the ocean increases the ocean temperature, which increases the number of phytoplankton in the ocean, which decreases the ocean temperature by blocking sunlight.
(E) As increase in the number of outdoor electric lights in an area increases the number of insects in the area, which increases the number of bats in the area, which decreases the number of insects in the area, which decreases the number of bats in the area.


6. The author of the passage would be most likely to agree with which one of the following hypotheses?

(A) Major volcanic eruptions sometimes cause average temperature in the hemisphere of the eruption to drop by more than a degree centigrade.
(B) Major volcanic eruptions can induce the El Niño phenomenon when it otherwise might not occur.
(C) Major volcanic eruptions do not directly cause unusually cold summers.
(D) The climatic effects of minor volcanic eruptions differ from those of major eruptions only in degree.
(E) El Niño has no discernible effect on average hemispheric temperature.


7. The information in the passage provides the LEAST support for which one of the following claims?

(A) Major volcanic eruptions have a discernible effect on global temperature.
(B) The effect of major volcanic eruptions on global temperature is smaller than was previously thought.
(C) Major volcanic eruptions have no discernible effect on regional temperature.
(D) Minor volcanic eruptions have no discernible effect on temperature in the hemisphere in which they occur.
(E) Minor volcanic eruptions have no discernible effect on temperature in the hemisphere opposite the hemisphere of the eruption.


8. The primary purpose of the last paragraph of the passage is to

(A) describe how the “year without a summer” differs from other examples of climatic feedback loops
(B) account for the relatively slight hemispheric cooling effect of a major volcanic eruption
(C) explain how regional climatic conditions can be significantly affected by a small drop in temperature
(D) indicate how researchers are sometimes led to overlook the effects of El Niño on regional temperature
(E) suggest a modification to the current model of how feedback loops produce changes in regional temperature