Infrared radiation in the energy of the atmosphere

A review of the processes in the Earth’s atmosphere that affect its energy is presented. The energy balance of the Earth and its atmosphere as a whole is considered, and the results of NASA programs for the monitoring of the global temperature and concentration of carbon dioxide and water in the atmosphere are presented. The spectra of the optically active components of the atmosphere in the infrared region are analyzed on the basis of classical methods of molecular spectroscopy. Spectroscopic data from the HITRAN databank facilitate analysis and lead to a simple scheme whereby the three main greenhouse components—carbon dioxide, water vapor in the form of free water molecules, and a water droplet—create an infrared radiation flux directed toward the Earth’s surface. This radiation is created by water molecules in the area of $0$–$580$ cm$^{–1}$, the atmospheric radiation in the region of $580$–$780$ cm$^{–1}$ is determined by the molecules of water and carbon dioxide. At frequencies above $780$ cm$^{–1}$, the contribution to atmospheric radiation due to water molecules is approximately $5\%$, and the rest is determined by the emission of water microdroplets, which partly enter some of the clouds. According to this model, at the present atmospheric composition, $52\%$ of the radiation flux on the Earth’s surface is created by atmospheric water vapor, and $32\%$ is due to microdroplets of water in the atmosphere, which include about $0.4\%$ of atmospheric water and $14\%$ of the radiation flux is determined by carbon dioxide molecules. Doubling the mass of atmospheric carbon dioxide, which will occur in about 120 years at the current rate of growth of atmospheric carbon dioxide, will lead to an increase in the atmospheric radiation flux towards the Earth by $0.7$ W/m$^2$, and a $10\%$ increase in the atmospheric concentration of water molecules increases this radiation flux by $0.3$ W/m$^2$. Doubling of the mass of atmospheric carbon dioxide in a real atmosphere leads to an increase in the global temperature of $2.0 \pm 0.3$ K in a real atmosphere, according to NASA data analysis. If the concentration of other components does not change, then the change in global temperature will be $0.4 \pm 0.2$ K, and the contribution to this change due to industrial emissions of carbon dioxide into the atmosphere is $0.02$ K.