Estimates of Molecular Absorption of Solar Radiation in the Atmosphere in the Past, Present, and Future

The current global warming is mainly associated with the emission of greenhouse gases into the Earth’s atmosphere (CO2, CH4, etc.), the atmospheric content of which continues growing, thus changing the Earth’s radiation balance and, hence, modern climate changes and increasing the number of extreme weather and climate events across the globe. One of the most important components of the atmospheric radiation balance is the molecular absorption of solar radiation by greenhouse gases. In this study, using the SCIATRAN model and calculations of solar radiation fluxes in the spectral range 1–4 μm, the molecular absorption of solar radiation by key anthropogenic greenhouse gases, CO2 and CH4, is analyzed for their past, present, and future concentrations in three latitude zones (tropics, mid-latitudes, and subarctic) and two seasons (winter and summer). The molecular absorption of incoming solar radiation in the 1–4 μm range by the greenhouse gases is found to be maximal in the tropics (153–168 W/m2) throughout the year. The molecular absorption of solar radiation by CO2 and CH4 is expected to increase to 0.8–1.2 W/m2 from 1750 to 2100. The forecasted increase in molecular absorption of solar radiation by the end of the 21st century is close to current estimates of changes in Earth’s radiation balance, which range from 0.5 to 1.0 W/m2. The global average increase in the molecular absorption of outgoing Earth’s thermal radiation is approximately 3–4 times greater than the increase in solar radiation absorption. Both of these changes driven by increasing greenhouse gas concentrations intensify the Earth energy imbalance and contribute to changes in the planet average temperature.