Final answer:
The greenhouse effect is the trapping of heat in Earth's atmosphere, where sunlight passes through but re-emitted infrared radiation from Earth is partially absorbed and re-radiated by greenhouse gases, leading to higher surface temperatures.
Step-by-step explanation:
The greenhouse effect refers to the trapping of heat within Earth’s atmosphere, a process that is crucial for maintaining the planet's habitable temperature. It works like a blanket: sunlight in the visible spectrum passes through the atmosphere and is absorbed by Earth's surface, which then re-emits the energy as infrared radiation. This infrared radiation has a longer wavelength due to the cooler temperatures of the Earth, which peaks around 300 K, unlike the Sun's peak at about 5800 K.
Greenhouse gases like carbon dioxide and methane are transparent to the incoming sunlight but they absorb this outbound infrared radiation. While some of this energy is radiated back into space, these gases also re-radiate a portion of it back towards Earth. This process increases the surface temperature above what it would be without these gases, as they essentially prevent some of the Earth's emitted heat from escaping into space.
Convection, or the transfer of heat by the macroscopic movement of fluid, plays a lesser role in this effect compared to radiation. The presence of greenhouse gases does not just block outward infrared radiation, but also the much smaller fraction of incoming infrared radiation in sunlight. However, the key factor is that these gases have a far greater effect on the outbound long-wave infrared radiation than they do on the short-wave infrared incoming from the Sun, which is why the two effects do not cancel each other out, leading to a net warming effect.