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Abstract Peak Neogene warmth and minimal polar ice volumes occurred during the Miocene Climatic Optimum (MCO, ca. 16.95–13.95 Ma) followed by cooling and ice sheet expansion during the Middle Miocene Climate Transition (MMCT, ca. 13.95–12.8 Ma). Previous records of northern high-latitude sea surface temperatures (SSTs) during these global climatic transitions are limited to Atlantic sites, and none resolve orbital-scale variability. Here, we present an orbital-resolution alkenone SST proxy record from the subpolar North Pacific that establishes a local maximum of SSTs during the MCO as much as 16 °C warmer than modern with rapid warming initiating the MCO, cooling synchronous with Antarctic ice sheet expansion during the MMCT, and high variability on orbital time scales. Persistently cooler North Pacific SST anomalies than in the Atlantic at equivalent latitudes throughout the Miocene suggest enhanced Atlantic northward heat transport under a globally warm climate. We conclude that a global forcing mechanism, likely elevated greenhouse gas concentrations, is the most parsimonious explanation for synchronous global high-latitude warmth during the Miocene.
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Importance of Longwave Radiative Forcing by Icy Clouds in Maintaining Miocene High‐Latitude Warmth
Abstract During the early‐to‐middle Miocene, global mean surface temperature (GMST) was approximately 8°C warmer than preindustrial, with a greater temperature increase in polar regions than the tropics. However, existing Miocene simulations underestimate this warmth, particularly in northern high latitudes. To address this discrepancy, we investigate the potential role of cloud phase. Using the Community Earth System Model, we conduct a paleoclimate sensitivity study focused on modifying ice nucleation and cloud phase partitioning schemes. These modifications increase the GMST, with a strong temperature rise in high latitudes and a muted increase in the tropics. These increases are driven by enhanced longwave cloud forcing, resulting from increased ice cloud amounts and cloud water content, and are amplified by water vapor and lapse rate feedbacks in the Arctic. Our study highlights that the improved parameterizations of cloud phase processes enhance models' capability to simulate Miocene high‐latitude warmth and potentially other warm climates.
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- PAR ID:
- 10580517
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 7
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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