This one's a doozy...

So E looked appealing as the correct answer to this question at first, but when I read the second part of that answer choice, I changed my mind...it states "The natural adjustment process, which occurs over millions of years, allows wide-fluctuations in the carbon level in the short term"...this doesn't weaken the argument in the passage at all. If anything, this reaffirms that nature has it "under control", and that the increase in carbon in the atmosphere caused by fossil fuel burning and the subsequent emissions are FINE, because nature will self-correct and even everything out. What E says to me is "don't worry about it, the increases may look alarming because they are so drastic, but this is very common and typical of nature's normal adjustment process"... Perhaps the use of the phrases "wide fluctuations" and "short term" is what has me confused. The passage states that a "sustained increase" would be a threat to human life. E doesn't mention a sustained threat at all - essentially, it justifies the environmentalists' care-free approach, stating that fluctuation is normal, and therefore any rise will NOT be long-term (sustained). Please help!