Recent enhancement of central Pacific El Niño variability relative to last eight centuries

Abstract

The far-reaching impacts of central Pacific El Niño events on global climate differ appreciably from those associated with eastern Pacific El Niño events. Central Pacific El Niño events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NIÑO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Niño4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Niño-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.

A Review of Paleo El Niño-Southern Oscillation

“…The only qualitatively consistent conclusion among different simulations seems to be that the 20th century ENSO was intensified [37,[64][65][66]. Additionally, the hydroclimate responses show agreement in volcano-induced ENSO anomaly patterns between CESM-LME and tree-ring data following the eruption year but they somehow contradict during the eruption year [68].…”

“…The tree-ring compilation also suggests a robust ENSO response to large tropical eruptions, with anomalous cooling in the east-central tropical Pacific in the year of eruption, followed by anomalous warming one year after. The new δ 18 O reconstruction from tree cellulose in Taiwan [37] (Figure 2f) also reveals a late 20th century enhancement of interannual variability compared to any other intervals of the 818-year-long reconstruction, associated with relatively warmer Nino 4 sea-surface mean temperature. Before the 20th century, the largest interannual excursions occurred during the early to mid-seventeenth century.…”

“…Strong ENSO signals have been detected in tree rings from the tropics and the mid-latitudes. Recently, tree-ring cellulose δ 18 O, instead of the conventional width, was also measured to infer the SST change over the tropical central Pacific [37,47]. On rare occasions, oxygen isotope ratios from ice cores at low latitudes can provide a high-resolution record of climate variability in the tropics during the last millennium [38].…”

“…[23] Lake sediment 10 ka Bainbridge Crater Lake, Galápagos Islands Conroy et al, 2008 [24] Lake sediment 10 ka El Junco Crater Lake, Galápagos Islands Z. Zhang et al, 2014 [25] Lake sediment 10 ka El Junco Crater Lake, Galápagos Islands Thompson et al, 2017 [26] Lake sediment 10 ka Bainbridge Crater Lake, Galápagos Islands Rein et al, 2005 [27] Marine [36] Tree-ring synthesis 1 ka 8 circum-Pacific clusters Liu et al, 2017 [37] Tree-ring isotope 1 ka Taiwan A direct assessment of past SST variability in the tropical Pacific spanning several decades can be retrieved from oxygen isotope measurements on fossil corals, collected from the tropical central and eastern Pacific [33,35,[39][40][41], or from mollusk shells well preserved in the archeological sites on the coast of Peru [42]. The carbonate oxygen isotopes (δ 18 O) in such marine records reflect variations in both SST and the hydrological cycle at as high as monthly resolution [43].…”

“…Also, the averaged modern δ 18 O variance is found to be intermediate between the millennium maxima and minima but the exceptionally intense 1997-1998 El Niño has no match in the earlier part of the millennium. [39], modified from Otto-Bliesner et al [66]; (c) Lithic concentration in a marine sediment from off Peru (% of maximum) [27]; (d) δ 18 O variability from marine sediments from the tropical eastern Pacific [32]; (e) Tree-ring synthesis from circum-Pacific sites (modified from Li et al [36]); (f) δ 18 O variability in tree-ring from Taiwan (modified from Liu et al [37]). Vertical bars denote the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the industrial warming, respectively.…”