How Does a Greenhouse Trap Heat?

Sunlight (short-wave radiation) passes through the transparent walls and roof of a greenhouse and is absorbed by soil, plants, and surfaces inside, which warm up and re-emit energy as infrared (long-wave) radiation. Glass and plastic are largely opaque to infrared, so this heat radiation is trapped inside rather than escaping. Additionally, the enclosure prevents warm air from rising and dissipating through convection — an effect sometimes called the "greenhouse effect" by analogy, though Earth's atmospheric greenhouse effect works primarily through gas absorption rather than physical barriers. Commercial greenhouses may use double-layered polycarbonate panels for better insulation and energy-efficient heating to extend growing seasons.