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Title: Simulating Pliocene warmth and a permanent El Niño-like state: The role of cloud albedo

We present that available evidence suggests that during the early Pliocene (4–5 Ma) the mean east-west sea surface temperature (SST) gradient in the equatorial Pacific Ocean was significantly smaller than today, possibly reaching only 1–2°C. The meridional SST gradients were also substantially weaker, implying an expanded ocean warm pool in low latitudes. Subsequent global cooling led to the establishment of the stronger, modern temperature gradients. Given our understanding of the physical processes that maintain the present-day cold tongue in the east, warm pool in the west and hence sharp temperature contrasts, determining the key factors that maintained early Pliocene climate still presents a challenge for climate theories and models. This study demonstrates how different cloud properties could provide a solution. We show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal SST gradients, an expanded warm pool and warmer thermal stratification in the ocean, and weaker Hadley and Walker circulations in the atmosphere. Having conducted a range of hypothetical modified cloud albedo experiments, we arrive at our Pliocene simulation, which shows good agreement with proxy SST data from major equatorial and coastal upwelling regions, the tropical warm pool, middle and high latitudes, andmore » available subsurface temperature data. As suggested by the observations, the simulated Pliocene-like climate sustains a robust El Niño-Southern Oscillation despite the reduced mean east-west SST gradient. In conclusion, our results demonstrate that cloud albedo changes may be a critical element of Pliocene climate and that simulating the meridional SST gradient correctly is central to replicating the geographical patterns of Pliocene warmth.« less
Authors:
 [1] ;  [1]
  1. Yale Univ., New Haven, CT (United States). Department of Geology and Geophysics
Publication Date:
Grant/Contract Number:
SC0007037
Type:
Accepted Manuscript
Journal Name:
Paleoceanography
Additional Journal Information:
Journal Volume: 29; Journal Issue: 10; Journal ID: ISSN 0883-8305
Publisher:
American Geophysical Union
Research Org:
Yale Univ., New Haven, CT (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Pliocene climate; cloud albedo
OSTI Identifier:
1454704

Burls, N. J., and Fedorov, A. V.. Simulating Pliocene warmth and a permanent El Niño-like state: The role of cloud albedo. United States: N. p., Web. doi:10.1002/2014PA002644.
Burls, N. J., & Fedorov, A. V.. Simulating Pliocene warmth and a permanent El Niño-like state: The role of cloud albedo. United States. doi:10.1002/2014PA002644.
Burls, N. J., and Fedorov, A. V.. 2014. "Simulating Pliocene warmth and a permanent El Niño-like state: The role of cloud albedo". United States. doi:10.1002/2014PA002644. https://www.osti.gov/servlets/purl/1454704.
@article{osti_1454704,
title = {Simulating Pliocene warmth and a permanent El Niño-like state: The role of cloud albedo},
author = {Burls, N. J. and Fedorov, A. V.},
abstractNote = {We present that available evidence suggests that during the early Pliocene (4–5 Ma) the mean east-west sea surface temperature (SST) gradient in the equatorial Pacific Ocean was significantly smaller than today, possibly reaching only 1–2°C. The meridional SST gradients were also substantially weaker, implying an expanded ocean warm pool in low latitudes. Subsequent global cooling led to the establishment of the stronger, modern temperature gradients. Given our understanding of the physical processes that maintain the present-day cold tongue in the east, warm pool in the west and hence sharp temperature contrasts, determining the key factors that maintained early Pliocene climate still presents a challenge for climate theories and models. This study demonstrates how different cloud properties could provide a solution. We show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal SST gradients, an expanded warm pool and warmer thermal stratification in the ocean, and weaker Hadley and Walker circulations in the atmosphere. Having conducted a range of hypothetical modified cloud albedo experiments, we arrive at our Pliocene simulation, which shows good agreement with proxy SST data from major equatorial and coastal upwelling regions, the tropical warm pool, middle and high latitudes, and available subsurface temperature data. As suggested by the observations, the simulated Pliocene-like climate sustains a robust El Niño-Southern Oscillation despite the reduced mean east-west SST gradient. In conclusion, our results demonstrate that cloud albedo changes may be a critical element of Pliocene climate and that simulating the meridional SST gradient correctly is central to replicating the geographical patterns of Pliocene warmth.},
doi = {10.1002/2014PA002644},
journal = {Paleoceanography},
number = 10,
volume = 29,
place = {United States},
year = {2014},
month = {9}
}