How do greenhouse gases contribute to global warming?

Greenhouse gases play a crucial role in global warming by absorbing infrared radiation and trapping heat in the Earth's atmosphere. When sunlight reaches the Earth, a portion of it is reflected back into space, while the rest is absorbed by the surface, warming it. The Earth then emits this energy in the form of infrared radiation.

Greenhouse gases, such as carbon dioxide, methane, and nitrous oxide, have molecular structures that allow them to absorb this infrared radiation effectively. After absorption, they re-radiate the energy in all directions, including back towards the Earth's surface. This process creates a "greenhouse effect," effectively insulating the planet and leading to an increase in average global temperatures.

As for the other options, while reflecting sunlight back into space plays a role in regulating temperatures, it is not the mechanism behind global warming. Filtering harmful UV rays primarily relates to ozone and does not cause warming. Furthermore, increased cloud formation can have complex effects on temperature, sometimes cooling the planet, but it does not directly cause global warming like the greenhouse effect does. Therefore, the absorption of infrared radiation by greenhouse gases is the primary reason for the warming of the Earth's atmosphere.