Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 13, 135-147, 2017
https://doi.org/10.5194/cp-13-135-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Feb 2017
Changes to the tropical circulation in the mid-Pliocene and their implications for future climate
Shawn Corvec1 and Christopher G. Fletcher2 1Department of Applied Mathematics, University of Waterloo, 200 University Ave W, Waterloo, Ontario, N2L 3G1, Canada
2Department of Geography and Environmental Management, University of Waterloo, 200 University Ave W, Waterloo, Ontario, N2L 3G1, Canada
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: Corvec, S. and Fletcher, C. G.: Changes to the tropical circulation in the mid-Pliocene and their implications for future climate, Clim. Past, 13, 135-147, https://doi.org/10.5194/cp-13-135-2017, 2017.
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Short summary
The mid-Pliocene warm period is sometimes thought of as being a climate that could closely resemble the climate in the near-term due to anthropogenic climate change. Here we examine the tropical atmospheric circulation as modeled by PlioMIP (the Pliocene Model Intercomparison Project). We find that there are many similarities and some important differences to projections of future climate, with the pattern of sea surface temperature (SST) warming being a key factor in explaining the differences.
The mid-Pliocene warm period is sometimes thought of as being a climate that could closely...
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