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Difficulty: Very hardWeakening Arguments

To address severe coastal erosion threatening its municipal beachfront, the town of Marrow Bay constructed a series of artificial offshore reefs designed to dissipate incoming wave energy. Over the two years following the installation, shoreline erosion rates along Marrow Bay decreased by 35 percent. Municipal engineers concluded that the artificial reefs were directly responsible for mitigating shoreline loss by successfully dampening wave impact forces. Which of the following, if true, most seriously weakens the municipal engineers' conclusion?

  1. During the two years following reef installation, an unusual regional shift in atmospheric pressure systems directed major ocean swells away from the entire coastline containing Marrow Bay.Answer
  2. B
    A parallel study of adjacent coastal communities without artificial reefs showed that their beachfronts experienced a marked increase in erosion over the same two-year period.
  3. C
    The long-term structural maintenance costs of the artificial reef over the next decade are projected to exceed the municipality's initial budget allocations.
  4. D
    The observed 35 percent reduction in coastal erosion failed to yield a corresponding increase in local beachfront tourism or municipal revenue.
  5. E
    Hydrological computer models executed prior to the reef construction had predicted an exact 35 percent reduction in incoming wave energy upon completion.

Answer

The correct option is the statement showing that during the two years following reef installation, an unusual regional shift in atmospheric pressure systems directed major ocean swells away from the entire coastline containing Marrow Bay.
The correct answer weakens the argument by introducing an alternative explanation for the observed decrease in coastal erosion. If broader atmospheric pressure shifts redirected major ocean swells away from the entire region, the reduction in erosion along Marrow Bay would have occurred even without the artificial offshore reefs. This severely undermines the engineers' claim of direct causality.

Step-by-Step Solution

1
Identify the premise and conclusion of the argument.
Premise: Shoreline erosion dropped by 35% after artificial reefs were installed. Conclusion: The artificial reefs caused the reduction in erosion by dampening wave impact forces.
Isolating the causal claim is essential for evaluating statements that undermine the argument.
2
Analyze the implicit causal vulnerability.
The argument assumes that no external factor coincidently reduced wave impact or shoreline erosion during the two-year timeframe.
Causal claims based on temporal correlation are vulnerable to alternative external explanations.
3
Evaluate the choices to find a statement that introduces a compelling alternative cause.
The statement regarding the regional shift in atmospheric pressure systems shows that ocean swells diminished across the entire region due to weather patterns, meaning erosion would have decreased regardless of the reef.
Demonstrating an independent external cause directly undermines the conclusion that the reef was responsible for the erosion reduction.

Key Concept

Causal Inference and Alternative Explanations in Critical Reasoning
Estimated Time:2m 0s
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Weakening Arguments

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