Abstract
The two components of the tropical overturning circulation, the meridional
Hadley circulation (HC) and the zonal Walker circulation (WC), are key to the
re-distribution of moisture, heat and mass in the atmosphere. The
mid-Pliocene Warm Period (mPWP; ∼ 3.3–3 Ma) is considered a very
rough analogue of near-term future climate change, yet changes to the
tropical overturning circulations in the mPWP are poorly understood. Here,
climate model simulations from the Pliocene Model Intercomparison Project
(PlioMIP) are analyzed to show that the tropical overturning circulations in
the mPWP were weaker than preindustrial circulations, just as they are projected to be in
future climate change. The weakening HC response is consistent with future
projections, and its strength is strongly related to the meridional gradient
of sea surface warming between the tropical and subtropical oceans. The
weakening of the WC is less robust in PlioMIP than in future projections,
largely due to inter-model variations in simulated warming of the tropical
Indian Ocean (TIO). When the TIO warms faster (slower) than the tropical
mean, local upper tropospheric divergence increases (decreases) and the WC
weakens less (more). These results provide strong evidence that changes to
the tropical overturning circulation in the mPWP and future climate are
primarily controlled by zonal (WC) and meridional (HC) gradients in
tropical–subtropical sea surface temperatures.
Citation
ID:
203238
Ref Key:
corvec2017climatechanges