Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century. But this...
GMAT Critical Reasoning : (CR) Questions
Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century. But this loss cannot be due to global warming. Recent data shows that temperatures of the air surrounding the mountain's glaciers never rise above freezing, so the glaciers cannot be melting. The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.
Which of the following is an assumption the earth scientist's argument requires?
Passage Analysis:
| Text from Passage | Analysis |
| Mount Kilimanjaro in Tanzania has lost \(90\%\) of its ice cover over the past century. |
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| But this loss cannot be due to global warming. |
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| Recent data shows that temperatures of the air surrounding the mountain's glaciers never rise above freezing, so the glaciers cannot be melting. |
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| The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it. |
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Argument Flow:
The scientist starts with an observed problem (\(90\%\) ice loss), immediately rejects the obvious cause (global warming), then provides temperature data as evidence, and finally offers alternative explanations that fit the evidence.
Main Conclusion:
Mount Kilimanjaro's ice loss cannot be due to global warming.
Logical Structure:
The argument relies on the premise that if temperatures never rise above freezing, then melting is impossible, so global warming can't be the cause. This creates a gap between 'no melting' and 'global warming didn't cause the ice loss' - we need to assume that global warming can only cause ice loss through melting, not through other mechanisms like affecting sublimation rates or snowfall patterns.
Prethinking:
Question type:
Assumption - We need to find what the scientist must believe to be true for their argument to work. The scientist concludes that global warming isn't causing the ice loss because air temperatures stay below freezing.
Precision of Claims
The scientist makes precise claims about temperature (never rises above freezing) and causation (global warming cannot be the cause). The key precision lies in the connection between air temperature and glacier melting.
Strategy
To find assumptions, we need to identify ways the conclusion could be falsified while keeping the stated facts intact. The scientist jumps from 'air temperature stays below freezing' to 'glaciers cannot be melting due to global warming.' We need to find what bridge assumptions make this logical leap valid.
This choice discusses what would happen if temperatures DID rise above freezing, but the scientist's argument is built on the premise that temperatures never rise above freezing. We don't need to assume anything about hypothetical scenarios where temperatures do rise above freezing, since the scientist's evidence specifically states this doesn't happen. This assumption isn't required for the argument to work.
The scientist mentions that insufficient snowfall contributes to ice loss, but doesn't need to assume any specific percentage decline in snowfall. The argument works as long as there's some reduction in snowfall contributing to the problem. A precise 90% decline isn't necessary for the logic to hold - even a smaller decline, combined with sublimation, could explain the ice loss.
This is the correct assumption. The scientist argues that global warming can't be causing the ice loss because melting isn't possible at current temperatures. But then the scientist proposes sublimation and lack of snowfall as the real causes. For this argument to work, we must assume that these alternative explanations aren't themselves caused by global warming. If global warming could increase sublimation rates or reduce snowfall, then global warming would still be the ultimate cause of ice loss, making the scientist's conclusion false.
The scientist doesn't need to assume anything about what has or hasn't been demonstrated about global warming's effects on Kilimanjaro in general. The argument is specifically about whether global warming is causing the ice loss through melting. Even if global warming has been clearly demonstrated to affect other aspects of the mountain, the scientist's narrow argument about melting could still be valid.
The scientist doesn't need to assume that sublimation and lack of snowfall could explain ice loss on other mountains. The argument is specifically about Mount Kilimanjaro. Whether these explanations work for other mountains is irrelevant to whether they explain what's happening on this particular mountain.