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Abstract Current global warming scenarios suggest surface temperatures may attain warmth last seen during periods of the early‐to mid‐Pliocene (5.3–3 Ma). Pliocene proxy reconstructions suggest sea surface temperatures 3–9°C warmer than today along midlatitude coastal upwelling sites. Recent climate modeling efforts focused on the mid‐Piacenzian period showed a good model‐data fit over midlatitude upwelling regions, but did not attempt to reproduce proxy records of early‐Pliocene warmth. Evidence also suggests that subtropical continents were wetter then; we show that warm coastal SSTs can be explained via such wetter land conditions near the upwelling sites. Using a global atmospheric model, we show that introducing idealized wetter conditions over subtropical continents leads to reductions in upwelling‐favorable wind events by weakening the land‐sea surface pressure gradient. The resulting weaker coastal upwelling of cold deep water can help explain the inferred warm coastal temperatures.
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Warmer Pliocene Upwelling Site SST Leads to Wetter Subtropical Coastal Areas: A Positive Feedback on SST
Abstract The early‐to mid‐Pliocene (5.3–3 Ma), characterized by warmer temperatures and similar CO2concentrations to present day, is considered a useful analog for future warming scenarios. Geological evidence suggests that during the Pliocene, many modern‐day desert regions received higher levels of rainfall and supported large perennial lakes and wetter vegetation types. These wetter conditions have been difficult to reconcile with model predictions of 21st century drying over most subtropical land regions. Using an atmospheric General Circulation Model, we show that underestimates of Pliocene rainfall over certain areas in models may be related to insufficient sea surface temperature (SST) warmth simulated over relatively local eastern boundary current regions. When SSTs off the coast of California are raised to more closely match some proxy reconstructions, rainfall increases over much of adjacent western North America. Over the southwestern USA, this increased rainfall is mainly due to a convergent monsoonal circulation that develops over late boreal summer. A smaller wintertime increase in precipitation also occurs due to differences in rainfall associated with midlatitude cyclones. Wetter land conditions are expected to weaken upwelling‐favorable coastal winds, so that increased rainfall caused by coastal SST warming suggests a positive feedback that could help sustain wet, Pliocene‐like conditions.
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- PAR ID:
- 10364568
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 37
- Issue:
- 2
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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