LSAT 150, Section 1, RC Passage 1, Greenhouse Effect

RC Passage 1 Explanation

PASSAGE TEXT: Evidence that the earth's atmosphere has warmed has become quite compelling, in part …

Paragraph Summaries

1. Recent evidence shows that Earth’s atmosphere has warmed in the last 100 years in a way that’s unusual compared to the previous 1,000 years. Other studies also strengthen the link between this warming and the greenhouse effect.
2. Earlier greenhouse models predicted more warming than scientists actually observed. Newer models fix this by accounting for airborne sulfates, which reflect solar energy and partly offset greenhouse warming.
3. Solar activity explains some short-term temperature fluctuations, but not the full recent rise. The best explanation is that greenhouse gases have raised Earth’s long-term equilibrium temperature.

Analysis

This passage is basically defending the greenhouse theory against two problems.

First problem: early greenhouse models seemed to overpredict warming. That gave opponents an opening. The response is sulfates. Greenhouse gases warm; sulfates cool by reflecting solar energy away. Once scientists include sulfates, the greenhouse model lines up better with observed temperatures.

Second problem: maybe the warming is just from solar variation. The passage gives that theory some credit. Solar activity does match some decade-by-decade fluctuations. But it can’t explain the whole long-term rise. The current increase goes beyond what solar-cycle models allow.

So the passage isn’t saying solar activity is irrelevant. It’s saying solar activity explains fluctuations around the old baseline, while greenhouse gases better explain why the baseline itself has shifted upward.

That “equilibrium temperature” point is the endgame. In the past, temperatures could move up or down, but they eventually returned to a long-term average. The recent rise looks different because it exceeds the normal range. So the author concludes something in the atmosphere has changed the average itself.