温室效应Greenhouse effect

能否吸收红外辐射取决于分子振动时偶极矩是否变化：N₂、O₂ 等同核双原子分子不吸收，CO₂（弯曲振动约 15 μm）、H₂O、CH₄、N₂O、氯氟烃等则能吸收。人为排放增加了温室气体浓度，使大气向外层空间辐射的高度上移、温度降低，地球系统吸收的能量多于放出的，形成“辐射强迫”，导致全球变暖。

A molecule absorbs infrared only if a vibration changes its dipole moment: homonuclear diatomics such as N₂ and O₂ do not, while CO₂ (bending mode near 15 μm), H₂O, CH₄, N₂O and CFCs do. Human emissions raise their concentrations, lifting the height from which the atmosphere radiates to space to colder levels, so Earth absorbs more energy than it emits. This radiative forcing causes global warming.

1824 年傅里叶指出大气像玻璃罩一样保温。1856 年尤尼斯·富特、1859 年丁达尔分别用实验证明 CO₂ 和水蒸气吸收热辐射。1896 年阿伦尼乌斯首次定量估算 CO₂ 加倍将使全球升温约 5–6 °C。1938 年卡伦德把观测到的变暖与燃烧化石燃料联系起来；1958 年基林开始连续观测大气 CO₂ 浓度。

In 1824 Fourier argued that the atmosphere keeps Earth warm like a glass cover. Eunice Foote in 1856 and Tyndall in 1859 showed experimentally that CO₂ and water vapour absorb heat radiation. In 1896 Arrhenius first estimated that doubling CO₂ would warm Earth by about 5–6 °C. Callendar in 1938 linked observed warming to fossil-fuel burning, and Keeling began continuous CO₂ measurements in 1958.

工业化以来全球平均气温已上升约 1.1–1.3 °C，导致冰川消融、海平面上升、极端天气增多和海洋酸化。1997 年《京都议定书》和 2015 年《巴黎协定》确立了减排框架，目标是把升温控制在 2 °C 以内并努力限制在 1.5 °C。化学领域的贡献包括替代能源、碳捕集、低碳工艺和替代高温室效应的制冷剂。

Global average temperature has risen about 1.1–1.3 °C since pre-industrial times, melting glaciers, raising sea level, increasing extreme weather and acidifying the oceans. The Kyoto Protocol (1997) and Paris Agreement (2015) set frameworks for cutting emissions, aiming to keep warming well below 2 °C and pursue 1.5 °C. Chemistry contributes alternative energy, carbon capture, low-carbon processes and refrigerants with low warming potential.