Understanding uncertainties in the response of ENSO to greenhouse warming

Collins, Matthew

doi:10.1029/2000gl011747

Cited by 107 publications

(78 citation statements)

References 16 publications

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“…The difference between the two versions of the GFDL model (a factor 1.21±0.12 higher standard deviation in CM2.0 and 0.88±0.13 in CM2.1) shows that the change in variability is due to small details of the model, similar to that seen in Collins (2000a). Note that the changes are of the same order as those observed in the SOI over the periode 1866-2004, so that the predicted change in standard deviation is often only significant with more than one ensemble member, and hence unobservable in reality.…”

Section: Enso In a Warmer Climatesupporting

confidence: 48%

El Niño in a changing climate: a multi-model study

2005

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Abstract. In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Niño -Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability.Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally.Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Niño-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations.Correspondence to: G. J. van Oldenborgh (oldenborgh@knmi.nl) Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Niño and La Niña events. Based on this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.

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Section: Enso In a Warmer Climatesupporting

confidence: 48%

El Niño in a changing climate: a multi-model study

2005

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“…Although this is a statistically significant difference at the 95% level using an F test, it has been noted that the amplitude of ENSO varies considerably on long time scales in HadCM3. In a 1000-yr run of HadCM3 using modern-day forcing, centuries with ENSO amplitude as low as that in the 6-ka run can be found (Collins 2000). Therefore, it is possible that the reduced ENSO activity at 6 ka is not the result of the external forcing but the result of internal variability within the model.…”

Section: A Modern-day and Mid-holocene Mean States Simulated By Hadcm3mentioning

confidence: 99%

ENSO in the Mid-Holocene according to CSM and HadCM3

Roberts

Battisti

Tudhope³

2014

Journal of Climate

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The offline linearized ocean-atmosphere model (LOAM), which was developed to quantify the impact of the climatological mean state on the variability of the El Niño-Southern Oscillation (ENSO), is used to illuminate why ENSO changed between the modern-day and early/mid-Holocene simulations in two climate modeling studies using the NCAR Climate System Model (CSM) and the Hadley Centre Coupled Model, version 3 (HadCM3). LOAM reproduces the spatiotemporal variability simulated by the climate models and shows both the reduction in the variance of ENSO and the changes in the spatial structure of the variance during the early/mid-Holocene. The mean state changes that are important in each model are different and, in both cases, are also different from those hypothesized to be important in the original papers describing these simulations. In the CSM simulations, the ENSO mode is stabilized by the mean cooling of the SST. This reduces atmospheric heating anomalies that in turn give smaller wind stress anomalies, thus weakening the Bjerknes feedback. Within the ocean, a change in the thermocline structure alters the spatial pattern of the variance, shifting the peak variance farther east, but does not reduce the overall amount of ENSO variance. In HadCM3, the ENSO mode is stabilized by a combination of a weaker thermocline and weakened horizontal surface currents. Both of these reduce the Bjerknes feedback by reducing the ocean's SST response to wind stress forcing. This study demonstrates the importance of considering the combined effect of a mean state change on the coupled ocean-atmosphere system: conflicting and erroneous results are obtained for both models if only one model component is considered in isolation.

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“…However, flux adjustments in HadCM3 have been shown to improve both these inadequacies (Inness et al, 2003;Turner et al, 2005) so these are unlikely reasons in this case. Earlier work with different versions of the Unified Model (Collins, 2000a(Collins, , 2000b saw increased ENSO activity at biennial timescales at 4 × CO 2 in HadCM2, but not HadCM3. This different response was not attributable to the removal of global flux corrections between HadCM2 and HadCM3.…”

Section: Reasons For the Biennial Tendency In Hadcm3ipfamentioning

confidence: 99%

The effect of doubled CO₂ and model basic state biases on the monsoon‐ENSO system. II: Changing ENSO regimes

Turner

Inness

Slingo

2007

Quart J Royal Meteoro Soc

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ABSTRACT:Integrations of a fully-coupled climate model with and without flux adjustments in the equatorial oceans are performed under 2 × CO 2 conditions to explore in more detail the impact of increased greenhouse gas forcing on the monsoon-ENSO system. When flux adjustments are used to correct some systematic model biases, ENSO behaviour in the modelled future climate features distinct irregular and periodic (biennial) regimes. Comparison with the observed record yields some consistency with ENSO modes primarily based on air-sea interaction and those dependent on basinwide ocean wave dynamics. Simple theory is also used to draw analogies between the regimes and irregular (stochastically forced) and self-excited oscillations respectively. Periodic behaviour is also found in the Asian-Australian monsoon system, part of an overall biennial tendency of the model under these conditions related to strong monsoon forcing and increased coupling between the Indian and Pacific Oceans. The tropospheric biennial oscillation (TBO) thus serves as a useful descriptor for the coupled monsoon-ENSO system in this case. The presence of obvious regime changes in the monsoon-ENSO system on interdecadal timescales, when using flux adjustments, suggests there may be greater uncertainty in projections of future climate, although further modelling studies are required to confirm the realism and cause of such changes.

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Understanding uncertainties in the response of ENSO to greenhouse warming

Abstract: Abstract.The response of ENSO to increases in greenhouse gases is found to be markedly different in climate change simulations using two different

Cited by 107 publications

References 16 publications

El Niño in a changing climate: a multi-model study

El Niño in a changing climate: a multi-model study

ENSO in the Mid-Holocene according to CSM and HadCM3

The effect of doubled CO₂ and model basic state biases on the monsoon‐ENSO system. II: Changing ENSO regimes

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Understanding uncertainties in the response of ENSO to greenhouse warming

Abstract: Abstract.The response of ENSO to increases in greenhouse gases is found to be markedly different in climate change simulations using two different

Cited by 107 publications

References 16 publications

El Niño in a changing climate: a multi-model study

El Niño in a changing climate: a multi-model study

ENSO in the Mid-Holocene according to CSM and HadCM3

The effect of doubled CO2 and model basic state biases on the monsoon‐ENSO system. II: Changing ENSO regimes

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Product

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The effect of doubled CO₂ and model basic state biases on the monsoon‐ENSO system. II: Changing ENSO regimes