Effects of greenhouse gases on Earth, Venus, and Mars: Beyond the one-blanket modela).

This article focuses on the physical mechanisms by which increasing atmospheric carbon dioxide (CO₂) affects planetary climate, providing a pedagogical module suitable for upper-level physics courses. It emphasizes two key concepts often missing in simpler treatments: the role of convection in linking surface temperature to the altitude of the outermost infrared (IR)-opaque atmospheric layer, and how rising CO₂ concentrations close spectral windows of IR absorption, thereby reducing outgoing thermal radiation. The discussion covers the energy balance of "naked" planets without atmospheres versus those with IR-active gases, explaining how atmospheres like Earth's and Venus's raise surface temperatures by trapping IR radiation and establishing a temperature gradient (lapse rate) through convection. The article further explores the complexity of molecular IR absorption spectra, the impact of pressure broadening, and positive feedbacks involving water vapor and surface reflectivity, concluding that increased CO₂ leads to higher surface temperatures by elevating the IR-thick atmospheric layer and narrowing IR transparency windows.