Reading a Press Release on Urban Trees and Heat
Read the following extract from a university press release and answer the questions using only the passage. 'A team compared 20 streets with mature street trees and 20 streets without trees in the same city. On summer afternoons, air temperature at 1.5 m above the pavement was on average 2.1°C lower on tree-lined streets. The authors caution that streets were not randomly assigned: tree-lined streets also had more shade and less asphalt. They conclude that planting trees may reduce street-level heat, but that the cooling effect cannot be separated from other differences between the streets. The city climate plan cites the study as evidence that 1,000 new trees will lower neighbourhood temperatures by about 2°C.' The exam asks candidates to identify the claim the researchers actually support, explain the function of the caution, and evaluate the climate plan's use of the study. No outside knowledge is required.
1. State the researchers' main conclusion in one sentence, using the passage's own level of certainty.
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The researchers' supported claim is that planting trees may reduce street-level heat, but the cooling effect cannot be separated from other differences between tree-lined and treeless streets. The passage does not support a definite causal claim of exactly 2.1°C; the 2.1°C is an observed average difference, and the authors use 'may' and 'cannot be separated' to signal uncertainty.
2. Explain why the authors mention that streets were not randomly assigned. What alternative explanation does this allow?
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The authors mention non-random assignment because it introduces confounding variables. Tree-lined streets also had more shade and less asphalt, so the temperature difference could be caused by shade or pavement rather than trees. Random assignment would tend to balance such differences between groups; without it, the comparison is observational and cannot isolate the tree effect.
3. The climate plan says 1,000 new trees will lower neighbourhood temperatures by about 2°C. Using only the passage, identify two weaknesses in this use of the study.
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Two weaknesses: first, the study is observational, so it cannot prove that 1,000 new trees will cause a 2°C drop; the passage explicitly says the effect cannot be separated from other differences. Second, the 2.1°C figure comes from existing mature street trees compared with streets without trees, not from a prediction about newly planted trees or an entire neighbourhood. The plan also changes scale from street-level air temperature to neighbourhood temperature, which the passage does not support.