I agree - the key word is will.

As A stands, it could mean that these gases will warm the atmosphere even more than they warm carbon dioxide, over the next 50 years.

Tiny quantities of more than thirty rare gases, most of them industrial by-products, threaten to warm the Earth’s atmosphere even more rapidly than carbon dioxide during the next fifty years.
(A) to warm the Earth’s atmosphere even more rapidly than carbon dioxide during the next fifty years (improper pacement of modifier)
(B) to warm the Earth’s atmosphere even more rapidly over the next fifty years than carbon dioxide will (OK)
(C) during the next fifty years to warm the Earth’s atmosphere even more rapidly than carbon dioxide (The same as A)
(D) a warming of the Earth’s atmosphere during the next fifty years even more rapid than carbon dioxide’s (threaten a warming => it could have been great if had been so)
(E) a warming of the Earth’s atmosphere even more rapid than carbon dioxide’s will be over the next fifty years (threaten a warming => it could have been great if had been so)

B: if you have a MGMAT SC guide this looks very similar to Chap 5, modifiers page 75.

The group arrived in New Orleans and decided to stay in a fancy hotel a week before Mardi Gras...

Should be written as


The group arrived in New Orleans a week before Mardi Gras and decided to stay in a fancy hotel.

The second one is correct b/c the modifier "a week before..." describes when the group arrived.


In your sentence, A the modifier "during the next fifty years" should be placed closest to what it is trying to modify.

We are comparing events.

Step 1:
2/3 split between options (A,B) and (C,D,E)

Step 2:
In option (A), comparison is between "to warm the Earth’s atmosphere even more rapidly" and "carbon-dioxide". So, the comparison is wrong.

Option (B) provides the best comparison

A. warm the Earth’s atmosphere even more rapidly than carbon dioxide

This statement is comparing warming the Earth's atmosphere to carbon dioxide. Illogical.

B. to warm the Earth’s atmosphere even more rapidly over the next fifty years than carbon dioxide will

This statement compares the warming of the Earth's atmosphere to the [warming] that carbon dioxide will. Logical

I think the statement compares the "Tiny quantities of more than thirty rare gases" with "carbon dioxide".

In this context, threaten to do something, not threaten warming...

C,D,E is out...
B/W
A and B, B is logical ... and meaningful

B, threaten to is the proper idiom and modifier "over the next 50 years" is in the proper place

Tiny quantities of more than thirty rare gases, most of them industrial by-products, threaten to warm the Earth's atmosphere even more rapidly than carbon dioxide during the next fifty years.

(A) to warm the Earth's atmosphere even more rapidly than carbon dioxide during the next fifty years
(B) to warm the Earth's atmosphere even MORE rapidly over the next fifty years THAN carbon dioxide will
(C) during the next fifty years to warm the Earth's atmosphere even more rapidly than carbon dioxide
(D) a warming of the Earth's atmosphere during the next fifty years even more rapid than carbon dioxide's
(E) a warming of the Earth's atmosphere even more rapid than carbon dioxide's will be over the next fifty years

GMATNinjaTwo Does (B) correctly compare MORE rapidly.... THAN carbon dioxide WILL? I have no idea why do we need WILL at the end of the sentence.
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Hi ziyuen,

Quantities threaten to warm atmosphere more rapidly than carbon dioxide.

Here you can deduce two meanings:

I. Quantities threaten to warm atmosphere more rapidly than Quantities threaten to warm carbon dioxide.

II. Quantities threaten to warm atmosphere more rapidly than carbon dioxide threaten to warm atmosphere

If you go by meaning then II is correct.

Now we know if can skip the words in parallelism if the meaning is not compromised. This is called ellipsis.

As you see "threaten to warm the atmosphere" is an action which is repeated twice in the sentence II. We can use verb WILL and elipse "threaten to warm the atmosphere", which can be understood.

Quantities threaten to warm atmosphere more rapidly than carbon dioxide WILL {threaten to warm atmosphere}

Ellipsis Trick: whenever you see parallelism in which some words or phrase is ellipsed then try to write out (in mind only ) the full sentence without skipping any word. This has more to do with the meaning and is widely tested in exam.

Hope this clears the doubt
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