V21-09

Official Solution:


Scientists studying climate change have found that global warming not only increases the temperature of the planet but also leads, on average, to an earlier arrival of the spring season and a later arrival of the autumn season. Though some argue that this effect on the seasons is advantageous because it increases the length of the summer growing season, leaders of the World Wildlife Fund fear that many animal species will not be able to adapt to the altered season lengths and will thus soon face extinction.

Which of the following, if true, provides the best evidence in support of the view held by the leaders of the World Wildlife Fund?


A. When spring arrives earlier than usual, most species of hibernating mammals are forced to emerge from hibernation earlier than usual and to find alternative food sources to supplement their regular diets.
B. As the planet's temperature rises, the average global sea surface temperature also rises, endangering several marine organisms that reside near the sea surface and that can only survive within very narrow temperature windows.
C. Many species of salmon rely on seasonal changes in temperature to signal the start of their annual migrations and will leave their freshwater birthplaces early if spring arrives early; as a result, the populations of several types of freshwater insects consumed by those species of salmon will grow exponentially, infesting thousands of acres of crops on which humans rely.
D. The young of many species of birds and rodents feed exclusively on caterpillars, whose metamorphosis into butterflies is triggered by seasonal changes in temperature.
E. As the length of the summer growing season increases, the amount of carbon emissions produced by humans gradually increases, exacerbating the increase in global temperatures that will likely endanger hundreds of animal species.


And we have some healthy debate going on here! Always a good thing

The conclusion, which is contained within the view held by the leaders of the World Wildlife Fund, is that many animal species will soon face extinction. So let's start by figuring out: why do the leaders of the WWF fear that this will happen

We are told that, based on scientific studies, global warming increases the temperature of the planet AND leads to an earlier arrival of the spring season and a later arrival of the autumn season. Is that change to the seasons necessarily a bad thing (or something WWF leaders should fear)? Some even argue that this change can be beneficial because "it increases the length of the summer growing season", so why are the WWF leaders fearful

WWF leaders fear that many animal species will not be able to adapt to the altered season lengths and that, as a result, those animal species will soon face extinction. This view would be supported by any evidence showing how altered season lengths could lead to an animal's extinction

Let's see if any of the answer choices provide such support

(A) This evidence demonstrates how altered season lengths can affect an animal, but it does not show that the change would affect the animal's ability to survive. Sure, the animals would be "forced" to find alternative food supplies, but there's no indication that they would fail to find those food sources. You'd have to make a huge assumption in order to conclude that this would contribute to extinctions. (A) can be eliminated

(B) This example shows how the increase in the temperature of the planet can endanger certain species, but leaders of the WWF are concerned about the altered season lengths, not about the increase in the temperature of the planet. This evidence suggests that global warming can be dangerous for certain species, but it does not support the reasoning of the WWF leaders. (B) can be eliminated.

(C) Here is an example of how the altered season lengths could have a negative impact on one species of animal: humans. However, it does not suggest that humans will be unable to adapt to the changes or unable to survive as a species because of the changes, so choice (C) can be eliminated

(D) As with choice (A), we have an example of how altered season lengths can affect an animal (the metamorphosis of caterpillars into butterflies is triggered by seasonal changes in temperature). But choice (D) also tells us how the effect on one animal will indirectly affect another animal: "the young of many species of birds and rodents feed exclusively on caterpillars". If caterpillars are the ONLY source of food for the young of many bird and rodent species and if caterpillars morph into butterflies earlier because of the early arrival of spring, then it's possible that all or most of the caterpillars will turn into butterflies before the young are hatched. This effect could severely diminish the survival rate of those young who have lost their only source of food

We certainly don't know for sure if the affected bird and rodents will be unable to adapt and survive, but choice (D) provides a solid example of how altered season lengths could lead to the extinction of certain species. Therefore, choice (D) definitely supports the view held by the WWF leaders

(E) This example shows a possible negative impact of the altered season lengths. However, choice (E) illustrates a GRADUAL change, suggesting that it will NOT cause any animals to face extinction anytime soon. Furthermore, this example does not show how animals will be unable to adapt to the altered season lengths and thus unable to survive. Rather, this scenario demonstrates how the altered season lengths will impact the temperature of the planet, which in turn will endanger many animal species. Although this evidence might contribute to the fears of the WWF leaders (because of the indirect effect on many animal species), it does not show us how an inability to adapt to the altered season lengths could lead to extinction. Choice (E) can be eliminated

Choice (D) provides the best evidence in support of the view held by the leaders of the World Wildlife Fund and thus is the best answer


Answer: D