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Difficulty: MediumIdentifying Underlying Assumptions

A metropolitan transit authority plans to replace its entire fleet of municipal diesel buses with electric buses powered by lithium-iron-phosphate batteries, claiming that this transition will significantly decrease the city's overall net greenhouse gas emissions over the next decade. The authority points to studies demonstrating that electric buses generate zero direct tailpipe emissions, whereas the current diesel fleet contributes twelve percent of the city's overall transportation-related carbon output.

Which of the following statements represent necessary assumptions upon which the transit authority's argument depends? Select all that apply.

  1. The greenhouse gas emissions generated by the power plants supplying electricity to charge the new bus fleet will be lower than the tailpipe emissions eliminated by removing the diesel buses.Answer
  2. B
    The financial expenditure required to purchase electric buses and install charging infrastructure will be fully recouped through fuel savings over the next ten years.
  3. The total greenhouse gas emissions produced during the manufacturing and distribution of the electric buses will not exceed the operational emission reductions achieved over the ten-year period.Answer
  4. D
    Electric bus technology will advance sufficiently over the next decade to increase single-charge driving range by at least fifty percent.
  5. E
    Manufacturers of diesel buses will immediately discontinue production of internal combustion vehicles following the transit authority's procurement decision.

Answer

The argument relies on two necessary assumptions: that upstream electricity generation emissions will not exceed the tailpipe emissions eliminated, and that emissions from manufacturing the electric buses will not outweigh operational emissions savings over the ten-year timeframe.
The transit authority claims that replacing diesel buses with electric ones will achieve a net reduction in greenhouse gas emissions over ten years. This claim moves from a premise about operational tailpipe emissions to a conclusion about total net emissions. To bridge this gap, two unstated conditions must hold true: first, the indirect emissions created by power plants to charge the batteries must be lower than the tailpipe emissions eliminated; second, the embodied emissions created during battery and vehicle production must not exceed the operational savings accrued over the ten-year window. Applying the Negation Test confirms that if either condition fails, net emissions will not decrease.

Step-by-Step Solution

1
Deconstruct the argument into premises and conclusion.
Premise: Electric buses produce zero tailpipe emissions, replacing diesel buses that cause 12% of transit carbon output. Conclusion: Net greenhouse gas emissions will significantly decrease over the next decade.
Identifying the gap between operational tailpipe savings and total net emissions highlights unstated logical assumptions.
2
Apply the Negation Test to the statement regarding electricity generation sources.
Negation: Power plant emissions from charging the buses will equal or exceed eliminated tailpipe emissions. Under this negated condition, net emissions do not decrease, breaking the conclusion.
A statement is a necessary assumption if its negation invalidates the conclusion.
3
Apply the Negation Test to the statement regarding vehicle manufacturing emissions.
Negation: Upfront manufacturing emissions will exceed ten years of operational reductions. Under this negated condition, net emissions over the ten-year period will increase or remain neutral, invalidating the claim.
The conclusion specifies a net reduction within a ten-year timeframe, making lifecycle emissions within that window essential.

Key Concept

Identifying Unstated Necessary Assumptions using the Negation Test
Estimated Time:2m 0s
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Identifying Underlying Assumptions

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