Comparison of observed and simulated tropical climate trends using a forward model of coral δ18O

D. M. Thompson, T. R. Ault, M. N. Evans, Julia Cole, J. Emile-Geay

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Abstract

The response of the tropical Pacific Ocean to future climate change remains highly uncertain, in part because of the disagreement among observations and coupled general circulation models (CGCMs) regarding 20th-century trends. Here we use forward models of climate proxies to compare CGCM simulations and proxy observations to address 20th-century trends and assess remaining uncertainties in both proxies and models. We model coral oxygen isotopic composition (δ18O) in a 23-site Indo-Pacific network as a linear function of sea-surface temperature (SST) and sea-surface salinity (SSS) obtained from historical marine observations (instrumental data) and a multimodel ensemble of 20th-century CGCM output. When driven with instrumental data from 1958 to 1990, the forward modeled corals (pseudocorals) capture the spatial pattern and temporal evolution of the El Nio-Southern Oscillation (ENSO). Comparison of the linear trend observed in corals and instrumental pseudocorals suggests that the trend in corals between 1958 and 1990 results from both warming (60%) and freshening (40%). From 1890 to 1990, the warming/freshening trend in CGCM pseudocorals is weaker than that observed in corals. Corals display a moderate trend towards a reduced zonal SST gradient and decreased ENSO-related variance between 1895 and 1985, whereas CGCM pseudocorals display a range of trend patterns and an increase in ENSO-related variance over the same period. Differences between corals and CGCM pseudocorals may arise from uncertainties in the linear bivariate coral model, uncertainties in the way corals record climate, undersensitivity of CGCMs to radiative forcing during the 20th century, and/or biases in the simulated CGCM SSS fields.

Original languageEnglish (US)
Article numberL14706
JournalGeophysical Research Letters
Volume38
Issue number14
DOIs
StatePublished - 2011

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climate
general circulation model
coral
trends
Southern Oscillation
sea surface salinity
sea surface temperature
warming
coral record
salinity
comparison
tropical climate
trend
radiative forcing
temporal evolution
temperature gradient
heating
isotopic composition
Pacific Ocean
climate change

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)
  • Geophysics

Cite this

Comparison of observed and simulated tropical climate trends using a forward model of coral δ18O. / Thompson, D. M.; Ault, T. R.; Evans, M. N.; Cole, Julia; Emile-Geay, J.

In: Geophysical Research Letters, Vol. 38, No. 14, L14706, 2011.

Research output: Contribution to journalArticle

Thompson, D. M. ; Ault, T. R. ; Evans, M. N. ; Cole, Julia ; Emile-Geay, J. / Comparison of observed and simulated tropical climate trends using a forward model of coral δ18O. In: Geophysical Research Letters. 2011 ; Vol. 38, No. 14.
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