Question

Scientist: A greenhouse gas, for example, carbon dioxide, forms a transparent layer that traps solar heat beneath it in the earth’s atmosphere. Atmospheric levels of carbon dioxide are currently increasing, causing the climate to warm—an effect that is predicted by at least one computer model of the greenhouse effect. But the warming that has occurred is a great deal less than what would be expected based on the model. Therefore, _______.

Which of the following most logically completes the scientist’s argument?

Option A
Option B
Option C
Option D
Option E

(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)

Solution

The Story

Scientist: A greenhouse gas, for example, carbon dioxide, forms a transparent layer that traps solar heat beneath it in the earth’s atmosphere. 

In this statement a scientist tells us a bit about GH gasses. A GH gas forms a transparent layer in the earth’s atmosphere. The layer traps solar heat below it. Carbon dioxide is an example of a GH gas.

Atmospheric levels of carbon dioxide are currently increasing, causing the climate to warm—an effect that is predicted by at least one computer model of the greenhouse effect.

Carbon dioxide is increasing. This increase is causing temperatures to rise. This rise in temperature is predicted by at least one computer model.

But the warming that has occurred is a great deal less than what would be expected based on the model. Therefore, _______. 

The model predicted a much higher temperature rise than what actually happened. We have a blank in the end. ‘Therefore’ indicates we need to fill the blank with something that can be inferred on the basis of the passage.

Gist: GH gasses warm the climate. Increasing levels of carbon dioxide (a GH gas) are causing temperatures to rise. A computer model had predicted the climate to be much warmer than the climate currently is.

(Since the given passage is not an argument, we are not going to try to find any gaps here.)

The Goal

We have to think of something that can be concluded (inferred) on the basis of the passage. One thing that comes to mind is: the model is flawed to some extent.

The Evaluation

(A) Incorrect. There is nothing in the passage to suggest that current measurements of carbon dioxide are flawed. So why would better measurements be needed? 

Do not make the mistake of thinking that the current measurements are not accurate must be why the model did not predict temperatures accurately. There is no such indication. There could be tonnes of reasons for why the model predicted inaccurately. 

On top of that, even if we assume that the model faltered because of poor measurements of atmospheric levels of CO2, can we infer that better measurements are needed? How about “better models are needed”? Basically, can we infer that there is a need? Is something not working perfectly enough to infer that it needs to be improved? 

John has a light in his room that has not been working for six months. Does that mean he needs to get the light fixed? Not necessarily. Maybe he has other light sources that are sufficient for his brightness needs (?). Maybe he has adjusted to the dark. The passage does not indicate any problem for which an accurate model of GH effect is needed.

(B) Incorrect. What is the definition of “greenhouse gas”? We’re told one thing that the gas is responsible for. Is that the definition of GH gas? Anyway, there is no indication at all in the passage towards changing the definition of GH gas. Baseless!

(C) Incorrect. Again, we need to be very precise with our understanding here. “There are other factors that contribute to the warming” is not the same as “the computer model failed to take into account all relevant factors”. This option does not even say that the model fails to consider all factors. It simply tells us that there are multiple factors that contribute to warming. That may be the case; that may not be the case. Probably, the model has considered all the factors there are. A model can be inaccurate even after considering all the factors. 

Let’s have some fun. Can we infer any or all of the following?

  • The model does not take all factors that impact temperature into consideration
  • There are factors besides the increase in greenhouse-gas emissions contributing to the warming COOLING of the climate 

(D) Correct.  We can infer this. The computer model gives an incorrect prediction. So, the model must be incorrect in some way. If the model functioned correctly in every aspect, could it make an incorrect prediction? Nope. The only reason the model would make an incorrect prediction is that it did something incorrectly. (could be an incorrect formula, could be not taking all factors into account, could be a units error.  We cannot infer what the error may be. However, there must certainly have been some error.)

(E) IncorrectNeed to be careful here too. Let’s first try to clearly understand what this option is saying.

‘The likely consequences of any warming of the climate’: probable consequences of warming.

‘Unlikely to be much less damaging’: not likely to be much less damaging. Is X much less damaging than Y? Unlikely. I.e., X is probably barely less, equal or more damaging than Y.

‘than predicted’: A is much more time-consuming than predicted. A was predicted to be time-consuming. It turned out to be much more time-consuming than was predicted.

This option is incorrect since the prediction was simply of the warming. Not of damage from consequences. Consequences of warming, and their damage are way beyond what’s being discussed in the passage. This cannot be inferred.

Additional Notes

Given the way the question is framed, it is an inference question. Remember the direction in an inference question. While going through each option, we do not ask: does this option help us justify the above passage? No! We instead ask: can we infer this based on the passage above?

SC Notes:
Comprehend the meaning of option E very clearly. Note how the comparison is presented. Understand what the word “predicted” refers to.

This solution was created by Anish Passi and Chiranjeev Singh.

If you have any doubts regarding any part of this solution, please feel free to ask in the comments section.

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