Der El Nino kommt alle zwei bis sieben Jahre und treibt die globalen Temperaturen kurzfristig nach oben. Immer wieder orakeln Forscher, dass es in Zukunft viel mehr El Ninos geben könnte, als Folge des menschengemachten Klimawandels. Lässt sich dieses Konzept anhand der Klimageschichte validieren? Gab es zu kalten Zeiten weniger El Ninos als in Warmzeiten? Eine Arbeit von Steinke et al. 2014 brachte Überraschendes: Während der Kleinen Eiszeit gab es nicht weniger, sonder sogar mehr El Ninos! Und während den Mittelalterlichen und Römischen Wärmeperioden gab es weniger El Ninos. Hier der Abstract:
Upwelling variability off southern Indonesia over the past two millennia
Modern variability in upwelling off southern Indonesia is strongly controlled by the Australian-Indonesian monsoon and the El Niño–Southern Oscillation, but multidecadal to centennial-scale variations are less clear. We present high-resolution records of upper water column temperature, thermal gradient, and relative abundances of mixed layer- and thermocline-dwelling planktonic foraminiferal species off southern Indonesia for the past two millennia that we use as proxies for upwelling variability. We find that upwelling was generally strong during the Little Ice Age (LIA) and weak during the Medieval Warm Period (MWP) and the Roman Warm Period (RWP). Upwelling is significantly anticorrelated to East Asian summer monsoonal rainfall and the zonal equatorial Pacific temperature gradient. We suggest that changes in the background state of the tropical Pacific may have substantially contributed to the centennial-scale upwelling trends observed in our records. Our results implicate the prevalence of an El Niño-like mean state during the LIA and a La Niña-like mean state during the MWP and the RWP.
Auch eine Arbeit von Tierney et al. 2015 nimmt den El Nino-Alarmisten den Wind aus den Segeln. Die Autoren finden in den tropischen Meerestemperaturen eine deutliche Ozeanzyklus-Signatur. Die El Nino-Dynamik jedoch blieb stabil und wurde weder durch natürliche noch anthropogene Faktoren verändert. Abstract:
Tropical sea surface temperatures for the past four centuries reconstructed from coral archives
Most annually resolved climate reconstructions of the Common Era are based on terrestrial data, making it a challenge to independently assess how recent climate changes have affected the oceans. Here as part of the Past Global Changes Ocean2K project, we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics, based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives. Validation exercises suggest that our reconstructions are interpretable for much of the past 400 years, depending on the availability of paleoclimate data within, and the reconstruction validation statistics for, each target region. Analysis of the trends in the data suggests that the Indian, western Pacific, and western Atlantic Ocean regions were cooling until modern warming began around the 1830s. The early 1800s were an exceptionally cool period in the Indo-Pacific region, likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century. Decadal-scale variability is a quasi-persistent feature of all basins. Twentieth century warming associated with greenhouse gas emissions is apparent in the Indian, West Pacific, and western Atlantic Oceans, but we find no evidence that either natural or anthropogenic forcings have altered El Niño–Southern Oscillation-related variance in tropical sea surface temperatures. Our marine-based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change.
Im Januar 2015 stellte eine Gruppe um Kathrin Keller eine Modellierungsstudie vor, in der die El Nino- La Nina Dynamik während der Kleinen Eiszeit zunimmt und während der Warmphase abnimmt:
Detecting changes in marine responses to ENSO from 850 to 2100 C.E.: Insights from the ocean carbon cycle
It is open whether El Niño–Southern Oscillation (ENSO) varies under climate change and how potential changes in the marine system are detectable. Here differences in the influence of ENSO on biogeochemical tracers, pH, productivity, and ocean temperature are analyzed in a continuous 850–2100 Common Era (C.E.) simulation with the Community Earth System Model. The modeled variance in ENSO amplitude is significantly higher during the Maunder Minimum cold than during the 21st century warm period. ENSO-driven anomalies in global air-sea CO2 flux and marine productivity are two to three times lower, and ocean tracer anomalies are generally weaker in the 21st century. Significant changes are detectable in both surface and subsurface waters and are earlier verifiable and more widespread for carbon cycle tracers than for temperature. This suggests that multitracer observations of both physical and biogeochemical variables would enable an earlier detection of potential changes in marine ENSO responses than temperature-only data.
Lewis & LeGrande 2015 schauten sich den El Nino-Verlauf der letzten 1000 Jahre im Modell an und fanden Schwankungen, jedoch keinen ENSO-Langfrist-Trend:
Stability of ENSO and its tropical Pacific teleconnections over the Last Millennium
Determining past changes in the amplitude, frequency and teleconnections of the El Niño-Southern Oscillation (ENSO) is important for understanding its potential sensitivity to future anthropogenic climate change. Palaeo-reconstructions from proxy records can provide long-term information of ENSO interactions with the background climatic state through time. However, it remains unclear how ENSO characteristics have changed on long timescales, and precisely which signals proxies record. Proxy interpretations are typically underpinned by the assumption of stationarity in relationships between local and remote climates, and often utilise archives from single locations located in the Pacific Ocean to reconstruct ENSO histories. Here, we investigate the long-term characteristics of ENSO and its teleconnections using the Last Millennium experiment of CMIP5 (Coupled Model Intercomparison Project phase 5; Taylor et al., 2012). We show that the relationship between ENSO conditions (NINO3.4) and local climates across the Pacific basin differs significantly for 100-year epochs defining the Last Millennium and the historical period 1906–2005. Furthermore, models demonstrate decadal- to centennial-scale modulation of ENSO behaviour during the Last Millennium. Overall, results suggest that the stability of teleconnections may be regionally dependent and that proxy climate records may reveal complex changes in teleconnected patterns, rather than large-scale changes in base ENSO characteristics. As such, proxy insights into ENSO may require evidence to be considered over large spatial areas in order to deconvolve changes occurring in the NINO3.4 region from those relating to local climatic variables. To obtain robust histories of the ENSO and its remote impacts, we recommend interpretations of proxy records should be considered in conjunction with palaeo-reconstructions from within the central Pacific.
Auch Zhong et al. 2017 weisen auf den Einfluss der Ozeanzyklen auf das El Nino-Geschehen hin:
A decadal tropical Pacific condition unfavorable to central Pacific El Niño
The frequency of central Pacific (CP) El Niño events displays strong decadal variability but the associated dynamics are unclear. The Interdecadal Pacific Oscillation (IPO) and the tropical Pacific decadal variability (TPDV) are two dominant modes of tropical Pacific decadal variability that can interact with high-frequency activities. Using a 500 year control integration from the Geophysical Fluid Dynamics Laboratory Earth System Model, we find that the difference in mean state between the low-frequency and high-frequency CP El Niño periods is similar to the decadal background condition concurrently contributed by a negative IPO and a positive TPDV. This decadal state features strengthened trade winds west of the International Date Line and anomalous cool sea surface temperatures across the central tropical Pacific. As such, positive zonal advection feedback is difficult to be generated over the central to western tropical Pacific during the CP El Niño developing season, resulting in the low CP El Niño frequency.
Die zahlreichen Hinweise auf natürliche die Variabilität und Langfrist-Stabilität des El Nino-Geschehens lassen ernsthaft an Alarmszenarien zweifeln, wie sie z.B. Mojib Latif zusammen mit Kollegen vorschlägt. Sie haben die Idee, dass der Klimawandel zu Super-El Ninos führen könnte. Damit steht er wohl mittlerweile ziemlich allein da.
