Water vapor and the dynamics of climate changes

TL;DR

This paper reviews how water vapor influences atmospheric dynamics across various climates, revealing non-monotonic circulation responses to temperature changes and highlighting the role of latent heat in climate variability.

Contribution

It provides a comprehensive overview of water vapor's dynamic effects on climate, including non-linear circulation responses and insights from idealized model simulations.

Findings

Atmospheric circulation can decrease in both warmer and colder climates.

Latent heat release significantly impacts atmospheric static stability.

Circulation changes are explored through idealized general circulation model simulations.

Abstract

Water vapor is not only Earth's dominant greenhouse gas. Through the release of latent heat when it condenses, it also plays an active role in dynamic processes that shape the global circulation of the atmosphere and thus climate. Here we present an overview of how latent heat release affects atmosphere dynamics in a broad range of climates, ranging from extremely cold to extremely warm. Contrary to widely held beliefs, atmospheric circulation statistics can change non-monotonically with global-mean surface temperature, in part because of dynamic effects of water vapor. For example, the strengths of the tropical Hadley circulation and of zonally asymmetric tropical circulations, as well as the kinetic energy of extratropical baroclinic eddies, can be lower than they presently are both in much warmer climates and in much colder climates. We discuss how latent heat release is implicated in such circulation changes, particularly through its effect on the atmospheric static stability, and we illustrate the circulation changes through simulations with an idealized general circulation model. This allows us to explore a continuum of climates, constrain macroscopic laws governing this climatic continuum, and place past and possible future climate changes in a broader context.