Abstract
AbstractClimate model simulations of El Niño–Southern Oscillation (ENSO) behavior for the last millennium demonstrate interdecadal to centennial changes in ENSO variability that can arise purely from stochastic processes internal to the climate system. That said, the instrumental record of ENSO does not have the temporal coverage needed to capture the full range of natural ENSO variability observed in long, unforced climate model simulations. Here we demonstrate a probabilistic framework to quantify changes in ENSO variability via histograms and probability density functions using monthly instrumental and coral‐based sea surface temperature (SST) anomalies from 1900–2005 and 1051–1150 CE. We find that reconstructed SST anomalies from modern corals from the southwest Pacific capture changes in ENSO variability that are consistent with instrumental SST data from the central equatorial Pacific. Fossil coral records indicate 100 years of relatively lower ENSO variability during part of the Medieval Climate Anomaly. Our results demonstrate that periods of reduced ENSO variability can last a century, far longer in duration than modern observations in the instrumental record of ENSO, but consistent with results from unforced climate model simulations.
Highlights
The El Niño-Southern Oscillation (ENSO) is a coupled ocean-atmosphere climate phenomenon with global impacts on temperature and precipitation patterns [Bjerknes, 1969; Ropelewski and Halpert, 1987]
We extend the procedure suggested in Trenberth [1997] and use descriptive statistics in tandem with probability theory by assessing histograms [Trenberth, 1997] and probability density functions (PDFs) [Parzen, 1962] of monthly resolved coral data to quantify changes in ENSO variability
Two recent compilations of ENSO-sensitive records find no statistically significant change in ENSO variability between the MCA and the Little Ice Age (LIA) and highlight the need for additional high-resolution proxy records to fully characterize the range of ENSO variability over the Common Era [Emile-Geay et al, 2013b; Henke et al, 2017]
Summary
The El Niño-Southern Oscillation (ENSO) is a coupled ocean-atmosphere climate phenomenon with global impacts on temperature and precipitation patterns [Bjerknes, 1969; Ropelewski and Halpert, 1987]. Given the wide range of ENSO behavior simulated in the absence of forcings external to the climate system [Wittenberg, 2009; Deser et al, 2012], it is critical to ascribe the degree to which anthropogenic warming and internal climate variability are each contributing to future projections of ENSO in climate models [Collins et al, 2010; DiNezio et al, 2013] This motivates the use of paleo-ENSO reconstructions as out-of-sample tests of climate model simulations [Gagan et al, 2000; Cobb et al, 2013; Schmidt et al, 2014]. The consistent SST response at Vanuatu during the most recent ENSO events increases our confidence in using coral records from the tropical, southwest Pacific for paleo-ENSO studies.
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