Reading Comprehension

PT150 · S1 · P1 · Q4 The Greenhouse Effect

A free, expert breakdown of this official LSAT Reading Comprehension question.

Save & drill this skill — build targeted practice sets from questions like this one
Video walkthroughs — watch every question solved step by step
81 official LSATs — as questions, timed sections & full-length tests

The following passage was written in the mid-1990s.

Topic

The evidence for global warming, the role of greenhouse gases, and evaluating alternative explanations for the recent unprecedented rise in Earth's atmospheric temperature.

Framework

Answer / Explain (with a touch of Present Debate: alternative explanations vs. greenhouse effect)

Main Point

Recent scientific evidence shows that the Earth’s average temperature has risen to levels not seen in the past 1,000 years, and while some alternative explanations exist, the best explanation for this unprecedented warming is the effect of greenhouse gases. The Most Valuable Sentence: Appears at the end of the last paragraph —

P1: Evidence for Unprecedented Warming and the Greenhouse Effect

The passage opens by telling us that compelling new evidence shows Earth’s atmosphere has recently warmed in a way that hasn’t happened in the last 1,000 years. This is based on analyzing things like ice samples, tree rings, and coral. The idea that greenhouse gases are causing this rise is getting stronger, even though it’s still debated.

P2: Addressing Problems with Early Models & the Role of Sulfates

Early computer models predicted even more warming than we’re seeing, which critics used to question the greenhouse theory. But new research shows that airborne sulfates (from volcanoes and pollution) actually reflect sunlight and offset some of the warming, explaining the mismatch and closing the gap between past predictions and what has actually happened.

P3: Considering Solar Variations as an Alternative Explanation

Another possible reason for the warming is changes in solar energy, but even though these solar cycles seem to track with temperature ups and downs over the decades, solar models can’t account for the full extent of the recent warming. The current rise exceeds what solar variation alone could produce, leading the author to conclude that greenhouse gases are still the main culprit.

It can be reasonably inferred from the passage that the author considers which one of the following most crucial in judging the success of a model developed to explain the global warming trend of the previous 100 years?

a strong correspondence between the
Too Weak: last few years
This answer is very close to what we want. But since the question stem is asking, "how would we judge the success of a model that's supposed to account for the last 100 years", it would be weird for the author to say, "As long as the model gets the last 3 or 4 years right, I trust it'll be successful when it comes to the other 97 years". This answer is made more tempting by the fact that the author's problem with the solar energy model is its failure to account for the recent rise of temperatures (which kind of sounds like the last few years of rising temperatures). But it goes against common sense to think that all the author cares about is the last few years, when it comes to accurately modeling the last 100 years.
26% picked this
that the model predicts an
Out of Scope: simple framework
The author never stresses that a correct model must have a simple elegance. He's just stressing that it needs to accurately match the observed data.
2% picked this
the extent to which the
Wrong Emphasis
In the second paragraph, the author would probably say that the greenhouse model was improved by being revised to account for sulfates, but he doesn't seem to be evaluating whether a model is legit or not based on how much it's been revised. He doesn't reject solar energy model because it's never been revised (or been revised too much). He rejects it because the model can't account for the entirety of the observed data points.
6% picked this
a close fit between the
Out of Scope: generally acknowledged
The author is never insisting that a successful model only postulate something that closely fits our general preexisting expectations. It seems like this author would be open to a model that has a surprising warming mechanism, as long as the model was able to successfully predict the observed measurements.
5% picked this
Correct
a long-term match between the
Why this is right
Just like (A), this gives us what we were looking for: the predictions from the model match the observed temperatures. What makes this better is that it says the author would like to see a long-term match (vs. just the last few years). Since this model is supposed to explain the last 100 years, it makes more sense to want the model to match all 100 years, not just the last few. Suppose that the unusually high temperatures had occurred in the 1960s, rather than in the last decade. The author would be just as troubled by a model that failed to account for that tall spike in temps in the 60s as he is by a model that fails to account for the tall spike in temps in recent years.
Skill tested: Author Opinion · how this choice captures the passage's function is the move to repeat next time.
62% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill

LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free