Final answer:
The greenhouse effect is primarily caused by the accumulation of greenhouse gases in Earth's atmosphere. This effect is responsible for trapping heat and warming the planet.
Step-by-step explanation:
The greenhouse effect is primarily caused by the accumulation of greenhouse gases in Earth's atmosphere. These gases include carbon dioxide (CO2), methane (CH4), and water vapor (H2O). When sunlight reaches the Earth's surface, some of it is absorbed and re-emitted as infrared radiation. The greenhouse gases trap this radiation, preventing it from escaping back into space, and thus warming the planet.