Estimates of solar radiation molecular absorption in the atmosphere in the past, present and future
P.M. Nerobelov1,2,3, G.M. Nerobelov1, Yu.M. Timofeyev1
1Saint Petersburg State University, St. Petersburg, Russia
2Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia
3St. Petersburg Federal Research Center of the Russian Academy of Sciences
Keywords: Earth radiation balance, molecular absorption, solar radiation, greenhouse gases, CO2, СН4, SCIATRAN
Abstract
Human activity is currently causing global warming of the planet, primarily due to the emission of greenhouse gases into the Earth's atmosphere (CO2, CH4, etc.). Despite international agreements and commitments made by various countries, the concentration of key greenhouse gases - CO2 and CH4 - in the atmosphere continues to rise. The increase in greenhouse gas levels leads to changes in the Earth’s radiation balance, which is the cause of modern climate changes affecting many 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 of 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. The calculations were performed for three latitude zones (tropics, mid-latitudes, and subarctic) and two seasons (winter and summer). According to the calculations, the maximal molecular absorption of incoming solar radiation in the 1-4 μm range by the greenhouse gases occurs in the tropics and reaches 153-168 W/m2 throughout the year. Over the period from 1750 to 2100, the molecular absorption of solar radiation by CO2 and CH4 is expected to increase to 0.8-1.2 W/m2. The projected 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. At the same time, 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 rising greenhouse gas concentrations, intensify the Earth energy imbalance and contribute to changes in the planet average temperature.
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