Carbon dioxide traps some of the infrared heat emitted from the Earth and prevents that heat from going back out into space (as it ordinarily would). The natural level of CO2 in the atmosphere is 0.03 %, yet even this small amount is enough to keep the earth at a temperature suitable for human habitation by acting like a covering of greenhouse glass over the planet.
二氧化碳具有吸收紅外線的「保溫」效果，在大氣中原本只佔百分之○・○三，地球因此像加裝了玻璃罩的溫室，溫暖而適合人居。