What is the primary radiative process by which methane contributes to the greenhouse effect?

Methane (CH4) primarily contributes to the greenhouse effect through the absorption of infrared radiation. The greenhouse effect itself is the process where certain gases in the atmosphere trap heat, preventing it from escaping back into space, thus warming the Earth. Methane molecules have a specific structure that allows them to efficiently absorb infrared radiation emitted by the Earth's surface. When the Earth warms up due to sunlight, it releases energy in the form of infrared radiation (heat). Methane molecules absorb this infrared radiation because the energy of the infrared photons matches the energy required to cause the methane molecule to vibrate and bend in specific ways. This absorption converts the infrared energy into kinetic energy within the methane molecule, causing it to heat up. The heated methane molecules then re-emit infrared radiation in all directions. Some of this re-emitted radiation escapes into space, but a significant portion is directed back towards the Earth's surface, contributing to further warming. Methane is a more potent greenhouse gas than carbon dioxide (CO2) on a shorter timescale because it absorbs infrared radiation more effectively per molecule. However, methane has a shorter atmospheric lifetime than CO2, meaning it breaks down more quickly in the atmosphere. The key radiative process is the absorption of infrared radiation at specific wavelengths due to the vibrational modes of the methane molecule, followed by the re-emission of infrared radiation, some of which warms the Earth's surface.