Correct Response: B. Cloud cover at night reduces the amount of heat that radiates into space by absorbing the heat radiating from the surface and re-radiating some of it back down toward the ground. The process slows the rate of surface cooling and traps heat near Earth's surface, keeping temperatures warmer than they otherwise would be. Evaporation rates (A) and hence evaporative cooling are usually lower at night in general, but this does not account for the warming effect of nighttime cloud cover. Atmospheric convection currents are not significant at night because solar heating is not available to warm the air near the surface and cause it to rise (C) and cloud cover at night tends to reduce condensation, consequently reducing the release of heat energy from condensation (D).
