Nature constantly adjusts the atmospheric carbon level. An increase in the level causes the atmosphere to hold more heat, which causes more water to evaporate from the oceans, which causes increased rain. Rain washes some carbon from the air into the oceans, where it eventually becomes part of the seabed. A decrease in atmospheric carbon causes the atmosphere to hold less heat, which causes decreased evaporation from the oceans, which causes less rain, and thus less carbon is washed into the oceans. Yet some environmentalists worry that burning fossil fuels may raise atmospheric carbon to a dangerous level. It is true that a sustained increase would threaten human life. But the environmentalists should relax—nature will continually adjust the carbon level.

Which one of the following, if true, would most weaken the argument in the passage?

(A) Plant life cannot survive without atmospheric carbon.
(B) It is not clear that breathing excess carbon in the atmosphere will have a negative effect on human life.
(C) Carbon is part of the chemical "blanket" that keeps the Earth warm enough to sustain human life.
(D) Breathing by animals releases almost 30 times as much carbon as does the burning of fossil fuels.
(E) The natural adjustment process, which occurs over millions of years, allows wide fluctuations in the carbon level in the short term.