No Reduction of Tropical Convection with Warming Expected from Theory or Models

Abstract

Theoretical arguments have for decades anticipated substantial weakening of tropical convection as the surface warms, yet convection-resolving models show no robust change in column-integrated convective mass transport and an increase in transported volume. Here we reconcile this apparent discrepancy by demonstrating that the two main theoretical arguments identify a redistribution, rather than a straightforward reduction, of convective motions. A commonly invoked hydrological argument accordingly captures a weakening at a single altitude that is offset by strengthening aloft as the troposphere expands upward. Further, reduced convective mass flux following atmospheric structures that rise with warming simply reflects decreasing air density aloft. Convective motions and transported water are shown to be highly invariant to surface warming along isotherms, and the ability to predict convective responses at individual altitudes is a manifestation of this invariance. Together, these findings recast and simplify long-standing expectations of how the tropical atmosphere will respond to warming.