6.1.4—Greenhouse effect

The natural greenhouse effect makes Earth habitable; human increases in long-lived greenhouse gases enhance it and warm the climate.

Short-wave sunlight enters; the surface emits long-wave infrared; gases absorb and re-emit some energy. Extra GHGs require a warmer surface–troposphere system to restore balance. Global warming is temperature trend; climate change includes wider responses.

Adding CO₂ does not add sunlight; it slows outgoing infrared, so equilibrium is restored at a higher mean temperature.

Specify natural versus enhanced effect and the short-wave/long-wave energy pathway.

The atmosphere does not warm by trapping all heat forever; energy still leaves, but the balance shifts.