Final answer:
The greenhouse effect is a natural phenomenon that occurs when gases in Earth's atmosphere trap heat, making the surface temperature warmer. It is similar to how a greenhouse traps heat for plants.
Step-by-step explanation:
The greenhouse effect is a natural phenomenon in which gases in Earth's atmosphere absorb and re-radiate heat, trapping thermal energy in the atmosphere and making the surface temperature of the Earth warmer than it would be otherwise. This effect is similar to how a greenhouse traps heat to create a warmer environment for plants. It is caused by the concentrations of various atmospheric gases, including carbon dioxide (CO₂), methane, nitrous oxide, and chlorofluorocarbons.