Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of

Question

Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century. But this loss cannot be due to global warming. Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing, so the glaciers cannot be melting. The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.

Which of the following is an assumption the earth scientist’s argument requires?

A. If temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would be the most likely explanation of the ice cover’s disappearance.
B. Annual snowfall on Mount Kilimanjaro has declined by at least 90 percent over the past century.
C. The sublimation and lack of snowfall referred to cannot be due to global warming.
D. It has not been clearly demonstrated that global warming has had any effect on Mount Kilimanjaro.
E. Sublimation and a lack of snowfall could fully explain the loss of ice cover on at least some mountains other than Kilimanjaro.

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Official Answer

C

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MartyMurray · Accepted Answer

Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century. But this loss cannot be due to global warming. Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing, so the glaciers cannot be melting. The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.

The argument works as follows.

It begins with background information:

Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century.

Then, comes the main conclusion:

this loss cannot be due to global warming

Next comes factual evidence:

Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing

Finally, we have two intermediate conclusions:

the glaciers cannot be melting

The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.

So, the factual evidence supports the intermediate conclusions, which in turn support the main conclusion that the loss cannot be due to global warming.

Which of the following is an assumption the earth scientist’s argument requires?

This is an Assumption question. So, the correct answer will be state something that must be true for the argument to work. In other words, the correct answer will be information necessary for the evidence to support the conclusion.

A. If temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would be the most likely explanation of the ice cover’s disappearance.

The conclusion of the argument is basically that global warming is not the explanation for the ice cover's disappearance.

So, the argument does not require assuming that, if things were different, global warming would be the explanation.

Eliminate

B. Annual snowfall on Mount Kilimanjaro has declined by at least 90 percent over the past century.

This choice is tempting because the passage says, "Mount Kilimanjaro in Tanzania has lost  90 percent  of its ice cover over the past century," and " The loss must be explained  by sublimation, or direct evaporation of the ice, and  by not enough snowfall  to replenish it."

At the same time, the argument does not require this choice because it doesn't have to be the case that the reason Mount Kilimanjaro has lost 90 percent of its ice cover is that annual snowfall has declined by 90 percent. After all, the ice cover could have decreased by 90 percent over time by declining a little each year, in other words, possibly because annual snowfall has decreased by a small percentage.

Eliminate.

C. The sublimation and lack of snowfall referred to cannot be due to global warming.

As we saw in our above analysis of the structure of the argument, the main conclusion is supported by the intermediate conclusion "The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it."

So, the argument jumps from "The loss must be explained by sublimation ... and by not enough snowfall," to the main conclusion "this loss cannot be due to global warming."

We see that the argument relies on the assumption stated by this choice for that jump to work. After all, if the sublimation and lack of snowfall CAN be due to global warming, then the argument doesn't work since, in that case, the intermediate conclusion that the decrease in ice cover is the result of sublimation and lack of snowfall doesn't mean the loss cannot be due to global warming.

Keep.

D. It has not been clearly demonstrated that global warming has had any effect on Mount Kilimanjaro.

This choice is tempting because the conclusion is "this loss (of ice on Mount Kilimanjaro) cannot be due to global warming." So, we might think the support for the conclusion requires this choice.

However, the truth is that this choice goes farther than what must be assumed for the argument to work. After all, the argument doesn't require assuming that global warming has not had "any effect" on Mount Kilimanjaro. Global warming could have had some effect and still not be the cause of the 90 percent decrease in ice cover.

Eliminate.

E. Sublimation and a lack of snowfall could fully explain the loss of ice cover on at least some mountains other than Kilimanjaro.

We don't need to assume that sublimation and a lack of snowfall explain the loss of ice cover on other mountains to conclude that they explain the loss of ice cover on Kilimanjaro.

Eliminate.
   
 Correct answer:  C

sachi-in · Answer

B. Annual snowfall on Mount Kilimanjaro has declined by at least 90 percent over the past century.
 (  apart from the reasoning provided in previous comment for rejecting B  )
high sublimation could also have contributed to lower ice cover, snowfall alone may not be responsible, maybe the share in reduction is atrributed to increased sublimation too

or maybe to cause 90% reduction in snow cover just a 20% reduction in snowfall is enough

This is not airtight logic

C. The sublimation and lack of snowfall referred to cannot be due to global warming.

If both secondary reasons  Sublimation & Snowfall  are attributed to our primary reason  global warming  then obviously  global warming  is (indirectly) responsible. It simply destroys the argument.

vic231 · Answer

MartyMurray

Why A is incorrect?

The argument mentions that, since the temperature never rose above freezing -> hence the glaciers cannot be melting and loss must be explained by sublimation or direct evaporation of the ice -> global warming is not the cause

Because temperature never rose above freezing, the argument concludes global warming is not the cause

But if we negate choice A i.e If temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would  not  be the most likely explanation of the ice cover’s disappearance, then the relation between temperature never rising above freezing and concluding that global warming is the cause gets broken.

MartyMurray · Answer

The conclusion is " this loss cannot be due to global warming." Simply put, the conclusion is that global warming is not the cause.

The support for the conclusion is that "Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing, so the glaciers cannot be melting."

So, the reasoning is basically that, since the temperatures never rose above freezing, global warming is not the cause.

Now, it's true that, if we negate choice (A), the logic of the connection between temperatures not rising above freezing and the conclusion becomes less clear.

Nevertheless, the negation does not break the argument because the negation is essentially "Even if temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would  not  be the most likely explanation of the ice cover’s disappearance."

So, with (A) negated, what we have is the idea that, either way, if temperatures did or did not rise above freezing, global warming is not the cause.

And that reasoning not really illogical.

After all, it could be that the fact that temperatures did not rise above freezing indicates that global warming is not the cause and that, also, even if temperatures did rise above freezing, global warming still isn't the most likely explanation for the ice cover’s disappearance  .

So, (A) is not a necessary assumption.

Ziniya · Answer

KarishmaB 
Could you please help to eliminate A.
I chose C because it's clearly an assumption, however had difficulty to eliminate A.

KarishmaB · Answer

(A) If temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would be the most likely explanation of the ice cover’s disappearance.

The argument talks about why 'global warming' is not the correct explanation - because temps don't rise above freezing so glaciers are not melting so global warming not responsible. The argument assumes that "temps rising above freezing" is  required  to consider global warming as the cause. It assumes nothing about what would make global warming the "most likely explanation." 
From the argument, all we can say is that i f temperatures often rose above freezing, global warming could be the explanation of the ice cover’s disappearance. Would it be still? We don't know. Would it be the most likely explanation? We don't know at all.

That is why (A) doesn't work.

Goldenfuture · Answer

My thinking & please tell me where I am wrong:

Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century. But this loss cannot be due to global warming. Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing, so the glaciers cannot be melting. The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.

Which of the following is an assumption the earth scientist’s argument requires?

A. If temperatures near Mount Kilimanjaro’s glaciers often rose above freezing, global warming would be the most likely explanation of the ice cover’s disappearance -  This is likely an inference or some extrapolation based on data. We will take premise on face of it.

B. Annual snowfall on Mount Kilimanjaro has declined by at least 90 percent over the past century. - Out of scope

C. The sublimation and lack of snowfall referred to cannot be due to global warming. - This sounds more like inference

D. It has not been clearly demonstrated that global warming has had any effect on Mount Kilimanjaro. - out of scope

E. Sublimation and a lack of snowfall could fully explain the loss of ice cover on at least some mountains other than Kilimanjaro. -  This shows the cover is mutually exclusive & completely exhaustive

MartyMurray   KarishmaB  - Is my thinking in-correct?

guddo · Answer

The scientist says Kilimanjaro’s ice loss isn’t from global warming because the glaciers aren’t melting, they’re disappearing through sublimation and not enough snow. But for that to prove global warming isn’t involved, the scientist has to assume that sublimation and the lack of snow aren’t themselves caused by global warming. If global warming were making the air drier or changing snow patterns, it could still be the real cause. So the argument depends on assuming that sublimation and low snowfall aren’t due to global warming.

That’s exactly what option C says. Go with C!

guddo · Answer

Let me try if you don't mind.

The scientist's argument says:

1. No melting (temps below freezing).
2. Therefore, no global warming.
3. It must be sublimation and low snow instead.

The leap from 1 to 2 only works if sublimation and low snowfall  are not themselves caused by global warming . If global warming is making the air drier (more sublimation) or reducing snowfall, then global warming could still be the root cause.

So the scientist  must assume  what option C says: sublimation and lack of snowfall aren’t due to global warming.

Your choice E says these factors could explain ice loss on  other  mountains. That doesn’t matter. The argument isn’t about other mountains; it’s about ruling out global warming for Kilimanjaro. E doesn’t fill the logical gap.

GG27 · Answer

Hi  MartyMurray

Thank you for providing such a detailed analysis. Just a quick doubt, wouldn't " But this loss cannot be due to global warming" be the main conclusion and the last two lines the intermediate conclusions? As the last two lines are supporting "but this cannot be due to global warming". Just wanted to understand how do we decide which conclusion is main when more than one conclusions are presented in the argument.

MartyMurray · Answer

Hi. I don't fully understand your question because you've said you have a doubt, but what you've suggested about the conclusions and support is the same as what I said in my explanation.

That said, I can say that the way to decide which conclusion is main is to determine what supports what. Intermediate conclusions will support the main conclusion, while the main conclusion will not support another conclusion.

GG27 · Answer

Hi Marty, thanks for the clarification. I just realized I inadvertently swapped the main conclusion and the intermediate conclusion in my question.
What I actually meant to ask was: In my opinion , " The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it ",  this line is supported by  "   But this loss cannot be due to global warming".  Therefore, while solving the question, in my head I considered the last sentence of the passage to be the main conclusion. After reading your detailed analysis, I realised that you considered " "But this loss cannot be due to global warming"  to be the main conclusion. So just wanted to understand that from you.

egmat · Answer

Hi GG27,

The question is a good one: when a passage holds two conclusions, how do you tell which one is main?

Both of your candidates really are conclusions - you are right about that. What separates them is direction: an intermediate conclusion is supported by something  and  goes on to support something else, while the main conclusion supports nothing further. So the whole job is working out which way the support runs.

Insert "therefore" both ways

Put the two claims in sequence with  therefore  between them, once in each order. Real support flows only one way, and the wrong way leaves a gap you can name out loud.

- "The loss must be explained by sublimation and not enough snowfall,  therefore  it cannot be due to global warming." This holds together - if the ice is leaving by sublimation rather than melting, the melting route is closed.
- "The loss cannot be due to global warming,  therefore  it must be explained by sublimation and not enough snowfall." This is a leap. Ruling out one cause does not establish another unless those are the only two candidates, and the scientist never says they are - dry wind, or ice physically carted away, would sit just as comfortably in that gap.

Only the first reading is defensible from the passage, so that is the direction the argument runs.

Cross-check with the evidence

The evidence given - temperatures never rise above freezing, so the glaciers cannot be melting - is about  melting , and melting is the mechanism global warming would work through. Evidence built to rule out warming tells you the warming claim is the destination. The sublimation sentence is what fills the hole once melting is closed off.

Same shape, stripped down:  "Sales fell. But the price rise isn't to blame - customers barely noticed it. It must be the delivery delays."  Run that backwards and you feel the leap at once.

One quick tell for next time: that  But  in the second sentence is the author denying what the opening fact invites you to believe - usually where the main conclusion sits.

Answer: C

Endgoal · Answer

Premise 1  / phenomenon the author tries to explain: Mount Kilimanjaro in Tanzania has lost 90 percent of its ice cover over the past century

Conclusion 1  (because it is the author’s opinion):It cannot be due to global warming

Premise 2 : Recent data shows that temperatures of the air surrounding the mountain’s glaciers never rise above freezing

Conclusion 2  (indicated by the word “so” which functions as “therefore”): glaciers cannot be melting

Conclusion 3  : The loss must be explained by sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it.

We now look at conclusions 1 and 3 because conclusion 2 does not directly state a possible cause of the ice cover loss.

Conclusion 1: cannot be due to  Global warming 
Conclusion 3: must be due to  sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it

Therefore, for the author " global warming ” is a completely different cause than “ sublimation, or direct evaporation of the ice, and by not enough snowfall to replenish it ”

This is assumption C.

Earth scientist: Mount Kilimanjaro in Tanzania has lost 90 percent of

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