PrepTest 148, Section 1, Question 25
Oceanographer: To substantially reduce the amount of carbon(51 more words not shown)
Which one of the following(8 more words not shown)
- ACarbon dioxide will(21 more words not shown)
- BEvaporation of warmer(24 more words not shown)
- CCarbon dioxide dissolved(34 more words not shown)
- DIt is the(20 more words not shown)
- ECarbon dioxide should(32 more words not shown)
Reading the argument
Can we capture enough carbon dioxide to make this worthwhile, and can we afford to do it? I'd also want to know whether putting so much of it into the ocean could harm marine life. Those are questions about the proposal, not facts we're given about its consequences.
What we’re looking for
The storage idea initially sounds plausible: the carbon dioxide would dissolve in deep water, and that water takes centuries to mix with the surface. The proposal is to put it in the water, not bury it beneath the seabed. For the necessary assumption, we need something this reasoning depends on. I don't have one precise prediction yet, so let's test which statement this reasoning actually needs.
Working the answers
- A
We need the carbon dioxide to dissolve, which the argument already says it would do. We don't need cold water to dissolve it much more thoroughly than warm water. It could dissolve equally thoroughly in both while deep water still offered the long-term storage claimed here.
- B
The argument concerns carbon dioxide put into deep water. Surface water might release substantial carbon dioxide while the newly stored carbon dioxide remained far below it. This doesn't address whether that deep storage works for the proposed period. We don't need all surface evaporation to avoid releasing carbon dioxide.
- CCorrect
I initially went along with the claim that slow mixing means long storage. But those are two different things: the water stays down for centuries, so the argument assumes the dissolved carbon dioxide won't get back into the atmosphere much sooner by some other route.
If the carbon dioxide escaped well before the deep water mixed with surface water, the slow mixing would not establish that it stays trapped for centuries. We don't need to invent a specific escape mechanism. The reasoning needs to exclude such an early escape for the water's mixing time to support the claimed storage time.
- D
The argument doesn't need density to be the main reason the carbon dioxide stays trapped. Some other feature could play the leading role while the proposed storage still worked. What matters is that the carbon dioxide remains below for the stated period, not which physical property deserves most of the credit.
- E
Centuries of storage are offered as a reason to support this plan. That doesn't make centuries a minimum requirement for ever using it. Perhaps several decades would still be useful, buying time to develop another solution. The oceanographer can support the proposal on the stated grounds without agreeing that every shorter storage period makes it unacceptable.
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