If the Composition of the Upper Atmosphere Were Changed So

If the composition of the upper atmosphere were changed so that a greater amount of terrestrial radiation escaped, what effect would this have on the Earth's climate?

A) There would be only a marginal effect since most of the heat the earth receives comes from the sun.
B) There would be a gradual increase in global temperatures.
C) There would be a gradual decrease in global temperatures.
D) It is difficult to predict the effect this change would have on global temperatures.