13 Feb 2023
 | 13 Feb 2023
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Amplified surface warming in the Southwest Pacific during the mid-Pliocene (3.3–3.0 Ma) and future implications

Georgia Rose Grant, Jonny H. T. Williams, Sebastian Naeher, Osamu Seki, Erin L. McClymont, Molly Patterson, Alan M. Haywood, Erik Behrens, Masanobu Yamamoto, and Katelyn Johnson

Abstract. Based on Nationally-Determined Contributions concurrent with Shared Socio-economic Pathway (SSP) 2–4.5, the IPCC predicts global warming between 2.1–3.5°C (very likely range 10th–90th percentile) by 2100 AD. However, global average temperature is a poor indicator of regional warming and Global Climate Models (GCMs) require validation with instrumental or proxy data from geological archives to assess their ability to simulate regional ocean and atmospheric circulation, and thus, to evaluate their performance for regional climate projections. The Southwest Pacific is a region that performs poorly when GCMs are evaluated against instrumental observations. The New Zealand Earth System Model (NZESM) was developed from the United Kingdom Earth System Model (UKESM) to better understand Southwest Pacific response to global change, by including a nested ocean grid in the Southwest Pacific with 80 % greater horizontal resolution than the global-scale host. Here, we reconstruct region Southwest Pacific sea surface temperature (SST) for the mid-Pliocene Warm Period (mPWP; 3.3–3.0), which has been widely considered a past analogue with an equilibrium surface temperature response of +3 °C to an atmospheric CO2 concentration of ~350–400 ppm, to assess the warming distribution in the Southwest Pacific. This study presents proxy SSTs from seven deep sea sediment cores distributed across the Southwest Pacific. Our reconstructed SSTs are derived from molecular biomarkers preserved in the sediment – alkenones (i.e., U37K' index) and isoprenoid glycerol dialkyl glycerol tetraethers (i.e., TEX86 index) and are compared with SSTs reconstructed from the Last Interglacial (125 ka), Pliocene Model Intercomparison Project (PlioMIP) outputs and transient climate model projections (NZESM and UKESM) of low to high range SSPs for 2090–2099 AD. Mean interglacial equilibrium SSTs during the mPWP for the Southwest pacific sites, were on average, 4.2 °C (1.8–6.1 °C likely range) above pre-industrial and show good agreement with model outputs from NZESM and UKESM under mid-range SSP 2–4.6 conditions. These results highlight that not only is the mPWP an appropriate analogue when considering future temperature change in the centuries to come, but also demonstrate that the Southwest Pacific region will experience warming that exceeds that of the global mean if atmospheric CO2 remains above 350 ppm.

Georgia Rose Grant et al.

Status: open (until 05 May 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-108', Anonymous Referee #1, 09 Mar 2023 reply
  • RC2: 'Comment on egusphere-2023-108', Anonymous Referee #2, 21 Mar 2023 reply

Georgia Rose Grant et al.

Georgia Rose Grant et al.


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Short summary
Regional warming will differ from global warming and climate models perform poorly in the Southern Ocean. Here, we reconstruct sea surface temperatures in the Southwest Pacific during the mid-Pliocene, a time 3 million years ago that represents the long-term outcomes of 3 °C warming, and is expected for the future. By comparing these results to climate model simulations, we show that the Southwest Pacific region will warm by 1 °C above the global average if atmospheric CO2 remains above 350 ppm.