On the response of the middle atmosphere to anthropogenic forcing

• Published in: Annals of the New York Academy of Sciences Vol. 1504; no. 1; pp. 25 - 43
• Main Author: Garcia, Rolando R.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.11.2021
• Subjects: Anthropogenic Effects; Anthropogenic factors; anthropogenic forcing; Atmosphere; Atmospheric chemistry; Atmospheric models; Carbon dioxide; global circulation and temperature; Greenhouse Gases; Human influences; Humans; Lower mantle; Mathematical models; Mesosphere; Middle atmosphere; Models, Theoretical; Numerical models; Ozone; Ozone depletion; ozone hole; Quasi-biennial oscillation; Robustness (mathematics); Simulation; Southern Hemisphere; Stratosphere; Temperature; Trends; Troposphere; anthropogenic forcing; middle atmosphere; quasi-biennial oscillation; global circulation and temperature; ozone hole
• ISSN: 0077-8923; 1749-6632
• DOI: 10.1111/nyas.14664

Anthropogenic forcing of the atmosphere by greenhouse gases (GHG) and ozone‐depleting substances has provided an unintended test of the robustness of current understanding of the physics and chemistry of the middle atmosphere, that is, the stratosphere and mesosphere. We explore this topic by examining how well anthropogenic changes can be simulated by modern, comprehensive numerical models. Specifically, we discuss the simulations of trends in global mean temperature; the development of the ozone hole and its impact on the dynamics of the Southern Hemisphere, both in the stratosphere and troposphere; trends in the stratospheric Brewer–Dobson circulation; and the response of the quasi‐biennial oscillation (QBO) to increasing burdens of CO2. We find that, in most of these cases, numerical simulation is able to reproduce observed changes and provide physical insights into the relevant mechanisms. Simulation of the QBO is on a less firm footing. Although many numerical models can now generate realistic QBOs, future projections of its behavior under the increasing burdens of GHG are inconsistent and even contradictory. In this brief review, we examine several aspects of the response of the middle atmosphere—the stratosphere and mesosphere—to anthropogenic forcing and what they reveal about our current understanding of middle atmosphere dynamics and photochemistry and their interactions with the troposphere. The examination shows that some aspects of the response are well understood and in excellent agreement with observations, while others are at least partly understood and can be modeled numerically with results that are consistent with available observations, although the precise mechanisms are not completely elucidated.