Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but chlorofluorocarbons (CFCs) in aerosols and other products have...
GMAT Critical Reasoning : (CR) Questions
Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but chlorofluorocarbons (CFCs) in aerosols and other products have thinned this protective layer. Evidence of this is the ozone hole that forms over the South Pole every Antarctic spring as temperatures drop below \(-78°\mathrm{C}\), the temperature at which ozone depletion occurs. Measurements of the ozone hole taken at various times this spring show that, compared with the same times the previous year, its area diminished by four million square kilometers. Nevertheless, scientists have not concluded that the ozone layer is recovering.
Which of the following would, if true, provide the strongest reason for the scientists' reaction to the measurements?
Passage Analysis:
| Text from Passage | Analysis |
| Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but chlorofluorocarbons (CFCs) in aerosols and other products have thinned this protective layer. |
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| Evidence of this is the ozone hole that forms over the South Pole every Antarctic spring as temperatures drop below –78°C, the temperature at which ozone depletion occurs. |
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| Measurements of the ozone hole taken at various times this spring show that, compared with the same times the previous year, its area diminished by four million square kilometers. |
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| Nevertheless, scientists have not concluded that the ozone layer is recovering. |
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Argument Flow:
The passage starts by explaining the ozone problem, then provides evidence of ongoing damage through the Antarctic ozone hole. It then presents what seems like good news - the hole shrunk significantly this year. However, it ends with the puzzling fact that scientists remain cautious despite this apparent improvement.
Main Conclusion:
There is no explicit main conclusion in this passage. Instead, it sets up a situation that needs explanation - why scientists aren't optimistic about the smaller ozone hole.
Logical Structure:
This isn't a traditional argument with premises supporting a conclusion. Rather, it's a setup passage that presents a puzzle: we have what appears to be good news (smaller ozone hole), but experts aren't drawing the positive conclusion we'd expect (that the ozone layer is recovering). The question asks us to find what would explain this seemingly contradictory scientific response.
Prethinking:
Question type:
Strengthen - We need to find information that would support or justify the scientists' cautious reaction to the seemingly positive news about the ozone hole shrinking.
Precision of Claims
The key claims involve specific measurements (4 million square kilometers reduction, \(-78°\mathrm{C}\) temperature threshold) and the scientists' specific reaction (not concluding recovery). We need to respect these precise facts while finding reasons that would make their caution reasonable.
Strategy
Since this is a strengthen question, we need to think about what additional information would make the scientists' cautious stance more justified or reasonable. The puzzle here is: why wouldn't scientists be optimistic when the ozone hole got significantly smaller? We should look for reasons that would explain why this one positive measurement doesn't necessarily mean the ozone layer is recovering overall.
This tells us the hole has grown every year for a decade except this year. While this shows a long-term worsening trend, it doesn't specifically explain why scientists wouldn't be optimistic about this year's improvement. In fact, breaking a decade-long trend of growth might seem like reason for cautious optimism. This doesn't strongly justify their reluctance to conclude the ozone layer is recovering.
The fact that the persistence duration of the ozone hole varies from year to year doesn't address why a significantly smaller hole area wouldn't be good news. We're told about area reduction, not duration changes, so this information about timing fluctuations doesn't help explain the scientists' caution about the area measurements.
If CFCs have been completely banned for several years due to international treaties, this would actually make scientists MORE likely to expect recovery and be optimistic about the smaller hole. This works against explaining their cautious reaction and would make their reluctance to conclude recovery seem unreasonable.
This is the correct answer. Since the passage states that ozone depletion occurs when temperatures drop below \(-78°\mathrm{C}\), unusual amounts of warm air mixing into polar regions would prevent the normal temperature conditions that cause depletion. This means the smaller hole could be due to atypical weather preventing normal depletion, rather than actual ozone layer recovery. This perfectly explains why scientists remain cautious - the improvement might be temporary and weather-related, not a sign of genuine healing.
While this shows that existing CFCs will continue destroying ozone for decades, it doesn't specifically explain why scientists wouldn't view this year's significantly smaller hole as at least a positive step. The long-term presence of CFCs is already established context, but doesn't address why this particular measurement wouldn't be seen as encouraging progress.