PrepTest 123, Section 2, Question 5
Scientist: Earth's average annual temperature has increased by(32 more words not shown)
Which one of the following,(13 more words not shown)
- AOnly some of(22 more words not shown)
- BMost of the(18 more words not shown)
- COver the last(15 more words not shown)
- DVolcanic dust and(20 more words not shown)
- EThe accumulation of(20 more words not shown)
Reading the argument
The Earth got warmer. Let's accept that fact and question the scientist's explanation for it.
The proposed explanation sounds plausible: gases build up in the atmosphere, block heat from escaping, and warm the planet. But why think that buildup was the main cause of the warming? A story that could explain an outcome isn't automatically the story that did explain it.
What if the sun got hotter?
That would give us another place to look for the extra heat. What else might supply it? Perhaps volcanic activity or asteroid impacts. These are guesses to investigate, not established causes. The point is to keep asking what else might explain the increase instead of accepting the first account we're offered.
What we’re looking for
We're asked for evidence against the scientist's explanation. I'd expect a fact supporting another cause of the warming. We don't have to deny that the temperature rose, and we don't have to prove the gases had no effect whatsoever. We need a reason to doubt that their buildup was the main explanation.
Working the answers
- A
I don't care where the gases came from. A gas from a natural source could trap heat just as a gas produced by industrial pollution could. The scientist's claim is about what the gases did, not who or what produced them. A changes the origin without challenging the proposed effect.
- BCorrect
This takes a different route from my prediction. Instead of giving another source of heat, it makes us question the timing of this proposed cause.
Most of the warming happened before 1940, while most of the gas buildup happened after 1940. How is a buildup concentrated later supposed to be the main explanation for warming that had largely happened already?
Imagine someone claiming that the United States caused ancient Rome to be founded. We'd immediately object that the supposed cause came after the event it allegedly caused. B presents a less extreme timing problem, but the same question matters: does the proposed cause arrive in time to explain the effect? This evidence makes the scientist's story less convincing without having to establish the true cause.
- C
This sounds like the hotter-sun prediction, which is exactly why we need to read it carefully. It says the Earth received more solar radiation in certain years than in others. That's variation within the century, not an increase over the century.
Suppose 1941 received more radiation than 1942. That might help explain why 1941 was warmer than 1942. It wouldn't explain why the 1900s were warmer than the 1800s. We'd need evidence of a longer-term increase in incoming radiation, and C never gives us that.
Saying Monday was cold and Tuesday was warm doesn't establish that this week was warmer than last week. The same problem applies here: fluctuations aren't the overall rise we're trying to explain.
- D
Reflecting sunlight away doesn't supply another source of warming. Nor does some reflection prevent the proposed greenhouse effect from operating: heat from sunlight that gets through could still be trapped. D doesn't establish a conflict between that process and the scientist's explanation.
- E
A large buildup of the proposed heat-trapping gases during the century of warming fits the account rather than challenging it. E doesn't prove that the gases caused the rise, and it doesn't itself tell us their timing within the century. But it gives us no evidence against the proposed explanation.
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