Scientist: A greenhouse gas, for example, carbon dioxide, forms a transparent layer that traps solar heat beneath it in the...

GMAT Critical Reasoning : (CR) Questions

Source: Official Guide

Critical Reasoning

Logically Completes

MEDIUM

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Notes

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Scientist: A greenhouse gas, for example, carbon dioxide, forms a transparent layer that traps solar heat beneath it in the earth's atmosphere. Atmospheric levels of carbon dioxide are currently increasing, causing the climate to warm—an effect that is predicted by at least one computer model of the greenhouse effect. But the warming that has occurred is a great deal less than what would be expected based on the model. Therefore, ______.

Which of the following most logically completes the scientist's argument?

better measurements of atmospheric levels of carbon dioxide are needed

the definition of "greenhouse gas" should probably be reconsidered

there are factors besides the increase in greenhouse-gas emissions contributing to the warming of the climate

the computer model of the greenhouse effect must be incorrect in some respect

the likely consequences of any warming of the climate are unlikely to be much less damaging than predicted

Solution

Passage Analysis:

Text from Passage	Analysis
A greenhouse gas, for example, carbon dioxide, forms a transparent layer that traps solar heat beneath it in the earth's atmosphere.	What it says: Explains how greenhouse gases like CO2 work - they create a see-through layer that traps heat from the sun What it does: Sets up the basic science background we need to understand the rest of the argument What it is: Scientific explanation/background information Visualization: Think of it like a blanket over Earth - sunlight gets in, but heat gets trapped underneath
Atmospheric levels of carbon dioxide are currently increasing, causing the climate to warm—an effect that is predicted by at least one computer model of the greenhouse effect.	What it says: CO2 levels are going up, which is making climate warmer, and computer models predict this should happen What it does: Connects the general science from before to what's actually happening now - builds on the greenhouse gas explanation What it is: Current factual observation + model prediction Visualization: CO2 levels: Rising ↗️, Climate temperature: Warming ↗️, Computer model says: "This should happen" ✓
But the warming that has occurred is a great deal less than what would be expected based on the model.	What it says: The actual warming we see is much less than what the computer model said we should see What it does: Creates a contradiction - challenges the model prediction from the previous statement What it is: Contrasting observation that creates a puzzle Visualization: Expected warming (model): 100%, Actual warming observed: 30% - there's a big gap!
Therefore, ______.	What it says: This is where we need to draw a conclusion from the contradiction we just learned about What it does: Signals that we need to figure out what logically follows from the model vs. reality mismatch What it is: Conclusion indicator - asking us to complete the logical reasoning

Argument Flow:

The scientist starts with basic greenhouse gas science, then shows that current CO2 increases and warming match model predictions in direction but not in magnitude. This creates a puzzle that needs explanation.

Main Conclusion:

The argument is incomplete - we need to determine what logically follows from the fact that actual warming is much less than the computer model predicted.

Logical Structure:

The premises establish a contradiction between model predictions and observed reality. The conclusion should explain what this mismatch tells us - likely that the model is flawed, incomplete, or missing important factors.

Prethinking:

Question type:

Logically Completes - We need to find a conclusion that logically follows from the gap between predicted warming and actual observed warming

Precision of Claims

The key claims involve precise comparisons: CO2 levels are increasing (quantitative trend), warming is occurring (qualitative change), model predictions exist (specific forecast), but actual warming is 'a great deal less' than expected (significant quantitative gap)

Strategy

Since we have a clear contradiction between model predictions and reality (model says more warming should happen, but we're seeing much less), we need to find what logically follows. The conclusion should address this discrepancy without questioning the facts given. We can conclude something about the model's accuracy, the presence of other factors, or the need for model revision.

Answer Choices Explained

better measurements of atmospheric levels of carbon dioxide are needed

Choice A: 'better measurements of atmospheric levels of carbon dioxide are needed' - This doesn't logically follow from the given information. We're not told there are problems with measuring CO2 levels - the issue is that the model's predictions don't match observed warming despite knowing CO2 is increasing. Better CO2 measurements wouldn't explain why actual warming is less than predicted.

the definition of "greenhouse gas" should probably be reconsidered

Choice B: 'the definition of "greenhouse gas" should probably be reconsidered' - This is too extreme and doesn't address the core issue. We're not questioning what greenhouse gases are or how they work - the argument accepts that greenhouse gases trap heat. The problem is specifically with the model's predictions versus reality, not with fundamental definitions.

there are factors besides the increase in greenhouse-gas emissions contributing to the warming of the climate

Choice C: 'there are factors besides the increase in greenhouse-gas emissions contributing to the warming of the climate' - This suggests additional factors are causing warming, but that would actually increase warming beyond model predictions. The issue is that we're seeing LESS warming than predicted, not more, so additional warming factors wouldn't explain this discrepancy.

the computer model of the greenhouse effect must be incorrect in some respect

Choice D: 'the computer model of the greenhouse effect must be incorrect in some respect' - This logically follows from the premises. When we have a clear contradiction between what a model predicts (significant warming) and what actually happens (much less warming), the most reasonable conclusion is that the model has some flaw, limitation, or error that causes it to overestimate warming effects.

the likely consequences of any warming of the climate are unlikely to be much less damaging than predicted

Choice E: 'the likely consequences of any warming of the climate are unlikely to be much less damaging than predicted' - This shifts focus to consequences and damage predictions, which is completely unrelated to the argument about model accuracy in predicting temperature changes. The argument doesn't discuss climate damage at all.

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