PrepTest 106

Topic: Science

Paragraph 1

• Paragraph note
  • Atmospheric debris produced by a major volcanic eruption has been hypothesized to have a cooling effect on Earth’s climate.
• Views, minor Meta-Structures, and the author's attitude
  • Fine dust and sulfuric acid droplets from an eruption can block sunlight, which is believed to result in a drop in Earth’s temperature.
  • Example: many believe the Tambora eruption in 1815 for the Earth’s “year without a summer” of 1816.
  • Author’s attitude: “may linger on” (first sentence); “persist for years” (first sentence); “researchers have generally thought” (second sentence); “many blame” (third sentence)

Paragraph 2

• Paragraph note
  • According to Clifford Mass and Davit Portman, volcanic eruptions don’t cause as much cooling as previously believed.
• Views, minor Meta-Structures, and the author's attitude
  • Mass and Portman conducted an analysis of nine volcanic eruptions, tracking global climate data for the years before and after
    • Examples: El Chichon in 1982 and Krakatau in 1883
    • Filtered out effect of El Nino-Southern Oscillation
      • El Nino warms the atmosphere - can mask cooling from an eruption but can also mimic cooling effect of an eruption if it ends as an eruption occurs
    • Author’s attitude: “seems plausible” (first sentence); “not as strong” (first sentence); “can mask the cooling” (fourth sentence); “can also mimic volcanic cooling” (fourth sentence)

Paragraph 3

• Paragraph note
  • Mass and Portman: minor eruptions have no effect on global temperature, while major eruptions cause a smaller drop than expected.
• Views, minor Meta-Structures, and the author's attitude
  • Mass and Portman’s analysis:
    • Accounted for El Nino
    • Major explosions that spit dust lower average temperature by half a degree centigrade or less in the hemisphere (northern or southern) where eruption occurred and in the opposite hemisphere
  • Author’s attitude: “came through more clearly” (first sentence); “contrary to what earlier studies had suggested” (second sentence); “no discernible effect” (second sentence); “cause a smaller drop than expected” (third sentence); “only half a degree” (third sentence)

Paragraph 4

• Paragraph note
  • Other researchers argue that a small temperature drop from an eruption can cause a significant decrease in regional temperature due to feedback loops.
• Views, minor Meta-Structures, and the author's attitude
  • Example of feedback loop: small temperature drop in NE US in early spring delays melting of snow, which leads to increased reflection of sunlight, which increases cooling.
    • Unusually cool air causes jetstream to move farther south than normal, causing more cold air to come in behind it, which further deepens cooling
    • This effect could cause the “year without a summer”
  • Author’s attitude: “could result in a significant regional fluctuation” (first sentence) “amplified by climatic feedback loops” (first sentence); “could, in turn, affect the jet stream” (third sentence); “could cause the stream to wander” (fifth sentence); “could be blown up” (sixth sentence)

Main Point: According to new research, major volcanic eruptions cause a smaller decrease in global temperature than previously hypothesized, but can have a significant depressive impact on regional temperature via feedback loops.

Paragraph 1, Sentence 2 (P1, S2) - Introduces volcano-climate hypothesis

P3, S3 - Mass and Portman show eruptions cause small decrease in global temperature

P4, S2 - Small decrease hypothesized to lead to significant regional decrease due to feedback loops

Reporting a Viewpoint: This passage uses a “Reporting a Viewpoint” Meta-Structure. The first paragraph introduces the topic of the passage: the hypothesis that dust thrown up by a volcanic eruption blocks sunlight and leads to a decrease in Earth’s average temperature (P1 S2). The author summarizes the research of Clifford Mass and Davit Portman, whose analysis shows that, contrary to earlier research, the effect of a major volcanic eruption on global temperature would be small (P2 S1, P3 S3). Finally, the author relates that other researchers hypothesize that climatic feedback loops could amplify even a small decrease in temperature to cause significant drops in regional temperature (P4 S1).

The main point in a Reporting A Viewpoint passage is the view held by the subject, in this case, Mass, Portman, and the other group of researchers mentioned in the fourth paragraph who posit the feedback loop hypothesis. The author does a clear and neutral job of tracing the volcano-climate hypothesis from its origins, through Mass and Portman’s research, to the feedback loop hypothesis. The author’s own opinion is largely absent from the passage.

Initially, this passage begins with the idea that scientists have believed the cooling effect of a volcanic eruption on global temperature to be significant. In fact, the author writes, people believe an eruption could cause a year without a summer. Then the author describes the research of Mass and Portman, stating that they believe the global effect of a major eruption is much less significant than previously believed. This statement seems to counter the original belief that eruptions have a significant climatic effect. Finally, the author discusses the hypothesis that climatic feedback loops can cause a large decrease in regional temperature, which could result in a year without a summer.

So the key distinction the author makes in the passage seems to be between the global effect of a major volcanic eruption and the regional effect of such an eruption. This distinction is key, and is something the careful test-taker should make note of.