If the greenhouse effect were absent, what would happen to Earth's average surface temperature?

• A. Surface temperature would drop dramatically, leading to global cooling
• B. Surface temperature would rise dramatically
• C. Surface temperature would remain the same
• D. Surface temperature would oscillate wildly

Answer: (A)

The greenhouse effect is what traps some of the heat that the surface emits so that the lower atmosphere stays warmer than it would otherwise be. If that trapping didn’t happen, heat would escape to space more easily, and the planet would cool to a much lower average temperature—roughly a 33°C drop, putting the average well below freezing. So the absence of the greenhouse effect leads to dramatic cooling, not warming, no change in average temperature, and not wild oscillations in the long run.