Abstract
Sea surface temperature (SST) variability of El Niño–Southern Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue. In its sixth assessment, the IPCC reports no systematic change in ENSO SST variability under any emission scenarios considered. However, comparison between the 20th and 21st century shows a robust increase in century-long ENSO SST variability under four IPCC plausible emission scenarios.
Highlights
Oscillation (ENSO) underpins its global impact, and its future change is a long-standing science issue
The summary for policymakers of the IPCC Sixth Assessment Report[1] (AR6) has reaffirmed that it is “very likely that the ENSO rainfall variability is projected to be amplified by the second half of the 21st century” in most emission scenarios, consistent with findings by previous studies of a stronger rainfall response to ENSO sea surface temperature (SST) variability even if ENSO SST variability itself does not change[2–4]
The AR6 report further states that “there is no model consensus for a systematic change in intensity of ENSO sea surface temperature (SST) variability over the 21st century in any of the shared socioeconomic pathways (SSP) scenarios assessed,” which we find does not reflect findings of the latest research
Summary
Sistent with previous results in terms of ENSO rainfall variability, which show a continuous increase after global mean temperature stabilizes[4]. Nonlinear Bjerknes feedback is important, in which once warm SST anomalies establish deep atmospheric convection in the equatorial eastern Pacific, the response of equatorial zonal wind anomalies increases nonlinearly to further sea surface warming[19], amplifying El Niño growth[10] An inter-model consensus of increased ENSO SST variability emerges in a subset of models that simulate a reasonably realistic nonlinear positive feedback[10]. The inter-model consensus, in the scenario with the strong mitigation pathway, highlights the need to consider the possibility of increased ENSO SST variability in addition to increased ENSO-induced rainfall variability. Received: 25 August 2021; Accepted: 6 January 2022; Published online: 31 January 2022
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