PT 65, S 1, Q 21 plz explain Forum

[hazara]

I dont understand why D is the correct answer choice.

Paragraph: So contrary to what they previously thought, a new research indicates that trees absord and store carbon dioxide less effectively than native grasses. Therefore, these incentives are helping hasten (speeding up) global warming.

Okay so wouldnt answer choice A be the correct one? it states: trees not only absorb carbon dioxide but also emit it.
if trees are emiting carbon dioxide they are hastening global warming.

why is D the correct choice? I mean if the new research indicates that trees absorb and store carbon dioxide less effectively than native grasses arent they still effective in slowing global warming but just to a lesser extent? and if that is the case then why are they claiming in the conclusion that trees hasten global warming. Only something that contributes to global warming can hasten the problem not something that slows it down.

In order for D to be correct that would mean the conclusion should state that global warming is slowing at a lesser extent then it would otherwise have if native grasses were planted rather than trees.

anyways, I would greatly appreciate for anyone to clarify this question.... Thanks.

[Jeffort]

(A) would be correct if it was a sufficient assumption question since adding that premise would guarantee that the conclusion is valid. Since this is a necessary assumption question, (A) is incorrect because it gives you more than the conclusion requires in order to be able to be true. It's a classic necessary assumption question trap answer since it's sufficient but not necessary.

The assumption in the argument is basically that you cannot both grow trees and grass in the same areas. By going with trees, which precludes the better option of growing grass, those countries would be doing something that will allow global warming to happen faster than it would if they used the same areas to grow grass instead of trees because grass absorbs CO2 more effectively than trees.

If you negate (A) it doesn't hurt the argument because there could still be other ways that growing trees instead of grass could contribute to global warming continuing to happen.

If you negate (D), it destroys the argument since the countries could still plant grass in order to lower CO2 levels in the atmosphere and slow down global warming even if they also plant more trees because of the government incentives.

[W$RKliveWELL]

I also got tricked up on this question read this it helped

http://www.manhattanlsat.com/forums/q21 ... t6337.html

[BPlaura]

It sounds like you may not have recognized that this question is looking for a NECESSARY assumption, rather than a SUFFICIENT assumption.

A necessary assumption is just something that's required in order for the conclusion to be possible. The conclusion, as you know, is that this practice of planting trees hastens global warming. That's a weird thing to conclude because even if (according to the premises) the trees are LESS effective at absorbing carbon dioxide than grasses, they are still absorbing some carbon dioxide - so how can it be that the practice of planting trees is actually detrimental? The answer must be that we're planting the trees instead of doing something that would be even more effective.

That's what answer choice (D) gives us - some of the trees are being planted where the (more effective) grasses would otherwise be growing. In order to test whether an assumption is necessary, you negate it and see whether it ruins the conclusion. The negation of (D) is that NONE of the trees are planted where the grasses would otherwise grow - if that were the case, the conclusion would no longer make sense because the trees wouldn't be hastening global warming; they'd just be sub-optimal. Since our negation ruins the conclusion, (D) is indeed necessary.

I'm not sure I agree with Jeffort - I wouldn't call answer choice (A) a sufficient assumption. In order for it to be sufficient, we'd have to know that the trees are emitting MORE carbon dioxide than they're absorbing. Jeffort, am I missing something here?

[Jeffort]

No, you're right Laura, my wording was a bit off and overly extreme. I wrote the post really fast and got interrupted before proofreading. Even though it sounds like a pretty strong strengthener, it isn't actually sufficient since we'd have to assume trees emit more CO2 than they absorb to 100% guarantee the conclusion.

I briefly thought about that issue after I wrote and was going to edit and tone down the phrasing of my first paragraph since I was mainly focused on criteria for necessary while writing first draft rather than checking if (A) would be a perfect SA answer. The phone rang with an important call right when I was about to proofread and edit so I just hit post, took the call and forgot to come back and edit. Good catch. Had I proofread, probably would have changed it to say that (A) is the type of strong sounding answer worthy of serious consideration for a SA question but is a typical attractive but overly broad/too strong to be necessary trap answer meant to sucker people that confuse/misunderstand the question types.

[hazara]

It sounds like you may not have recognized that this question is looking for a NECESSARY assumption, rather than a SUFFICIENT assumption.

A necessary assumption is just something that's required in order for the conclusion to be possible. The conclusion, as you know, is that this practice of planting trees hastens global warming. That's a weird thing to conclude because even if (according to the premises) the trees are LESS effective at absorbing carbon dioxide than grasses, they are still absorbing some carbon dioxide - so how can it be that the practice of planting trees is actually detrimental? The answer must be that we're planting the trees instead of doing something that would be even more effective.

That's what answer choice (D) gives us - some of the trees are being planted where the (more effective) grasses would otherwise be growing. In order to test whether an assumption is necessary, you negate it and see whether it ruins the conclusion. The negation of (D) is that NONE of the trees are planted where the grasses would otherwise grow - if that were the case, the conclusion would no longer make sense because the trees wouldn't be hastening global warming; they'd just be sub-optimal. Since our negation ruins the conclusion, (D) is indeed necessary.

I'm not sure I agree with Jeffort - I wouldn't call answer choice (A) a sufficient assumption. In order for it to be sufficient, we'd have to know that the trees are emitting MORE carbon dioxide than they're absorbing. Jeffort, am I missing something here?

thanks guys and i see what yall are saying but my beef was with the conclusion that was drawn by the author. it didnt make sense. it still doesnt make sense. I think of it this way. If person A builds a machine that will protect the environment and does so but not as good as person B, How can person A be worsening or speeding up environmental pollution. It just makes no sense.

[BPlaura]

To use your example:

If we're using person A's (less effective) machine when we would otherwise have been using person B's machine, even though we're still helping the environment a little, we would have been helping it more if we stuck to using machine B. So in that scenario we're "hastening" global warming because machine B would be more effective than machine A, but we're using A anyway. The conclusion isn't actually saying that we're harming the environment by growing trees; it's just saying that the onset of global warming would be slower if we just stuck to growing the grasses.

And Jeffort, no worries, I've definitely done the same thing before. I was just having a "hmmmm, am I being an idiot here?" moment.