Absorption and Scattering Interactions with Atmospheric Composition: How this has shaped the Trends in Climate

A distinguished legacy of Professor Kuo-Nan Liou in the atmospheric sciences is the fundamental connections he pioneered between the electromagnetic theory of absorption and scattering and its application to the interaction of solar and longwave radiation fields with atmospheric constituents (gases, aerosols, and clouds). The formalisms have yielded profound advances in our understanding of the changes in the radiative energy disposition in the atmosphere-surface system, with consequences for the interpretation of climate forcings and feedbacks. Basic theory and mathematical modeling indicate that the optical effects of changes in atmospheric gas and aerosol concentrations over the past century have perturbed the planetary radiative energy budget. We investigate the manner in which the natural and anthropogenic changes in atmospheric species have driven changes in the surface and atmosphere heating. The changes have impacted the thermodynamic budget, large-scale dynamics, temperature and precipitation. Satellite observations over the past two decades reveal an increase in the Earth’s radiation imbalance which can be interpreted in the context of forcing and feedback mechanisms. We utilize IPCC AR6-class climate models to investigate the roles of the plausible causal factors, which are in some ways contrasting, to understand the changes in the radiative interactions with atmospheric composition, leading to climate change. This understanding, along with a characterization of the uncertainties, is pivotal to projecting the global and regional climate in the 21^st century in response to emissions scenarios of greenhouse gases and aerosols.