PrepTest 154, Section 2, Question 23
The effects of global warming on the polar(58 more words not shown)
Which one of the following,(12 more words not shown)
- AAs global temperatures(23 more words not shown)
- BAs global temperatures(34 more words not shown)
- CAs sea temperatures(32 more words not shown)
- DAs sea temperatures(24 more words not shown)
- EAs global temperatures(32 more words not shown)
Reading the argument
Warmer water should melt more ice. So why would the ice caps get bigger? That's the result the models predict under the same warming scenario: seawater becomes warm enough to melt the caps considerably, yet their total volume increases. We shouldn't explain away one fact by denying the other. We need a way for both to happen.
Perhaps ice is being added somewhere even while ice is melting elsewhere. But it has to be added to the polar caps themselves. Growth in unrelated ice outside the caps wouldn't explain the stated increase in their volume. I don't yet have a mechanism; I know what it would need to accomplish.
What we’re looking for
For the paradox question, look for an effect of warming that adds ice or otherwise explains the caps' growth despite the melting. Merely stopping a decline wouldn't be enough. The surprising fact is an increase.
Working the answers
- ACorrect
Warming increases evaporation, which leads to more snowfall at the polar caps. That snow then melts and refreezes as ice. Now we have a source of additional ice alongside the loss from warmer seawater.
The two processes can operate at once: some existing ice melts, while additional snowfall supplies new ice. If the additions outweigh the loss, the caps grow overall. A provides the missing mechanism that makes the apparently conflicting predictions understandable, without denying that the warmer water melts ice.
- B
Stabilizing the size doesn't explain an increase. Less contact with warm water could help explain why the caps stop shrinking, but the models say their volume grows. B ends at a neutral result when we need a positive change. Read all the way through the mechanism to the outcome it actually supplies.
- C
Faster melting points toward less ice, not more. It reinforces the part of the situation we already understand: warmer water can melt the caps. We still need to explain why their volume would increase despite that loss.
- D
A lower freezing temperature means the seawater must get colder before it freezes. It doesn't mean freezing becomes easier. In a warming scenario, that change doesn't supply a reason for more ice to form. Be careful not to read 'lowers the temperature needed' as 'lowers the difficulty.' Those would point in different directions.
- E
Smaller temperature differences between hot and cold climates don't tell us why ice accumulates at the poles. Those differences could narrow in several ways, and E never connects the change to additional polar ice. The clouds sound promising after A's evaporation story, but only A continues through to snowfall and new ice at the location we need.
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