The response of subtropical highs to climate change

Purpose of Review
Subtropical highs are an important component of the climate system with clear implications on the local climate regimes of the subtropical regions. In a climate change perspective, understanding and predicting subtropical highs and related climate is crucial to local societies for climate mitigation and adaptation strategies. We review the current understanding of the subtropical highs in the framework of climate change.

Recent Findings
Projected changes of subtropical highs are not uniform. Intensification, weakening, and shifts may largely differ in the two hemispheres but may also change across different ocean basins. For some regions, large inter-model spread representation of subtropical highs and related dynamics is largely responsible for the uncertainties in the projections. The understanding and evaluation of the projected changes may also depend on the metrics considered and may require investigations separating thermodynamical and dynamical processes.

Summary
The dynamics of subtropical highs has a well-established theoretical background but the understanding of its variability and change is still affected by large uncertainties. Climate model systematic errors, low-frequency chaotic variability, coupled ocean-atmosphere processes, and sensitivity to climate forcing are all sources of uncertainty that reduce the confidence in atmospheric circulation aspects of climate change, including the subtropical highs. Compensating signals, coming from a tug-of-war between components associated with direct carbon dioxide radiative forcing and indirect sea surface temperature warming, impose limits that must be considered.