Question aimed mainly at AbruptSLR because he has mentioned some evidence about this topic (but rather obliquely) before but anybody else is welcome to comment. In a very simplistic way I see the default position to be that the (Pacific) ocean is absorbing more energy (temperature) as compared to the atmosphere. In El Nino conditions this changes and the main effect is (or main driver?) is that the Pacific ocean transmits energy to the atmosphere. Since with AGW the ocean is absorbing 90% of the additional energy then the differential between the (Pacific) ocean and the atmosphere is increasing (Is this correct?). Since El Nino is a main method for attempting to equalise this imbalance I would expect characteristics of El Nino to change. It seems that there are 3 main ways this could occur: El Ninos become more frequent, El Ninos become longer or El Ninos become stronger. Do the climate models make a prediction about this? To bring the discussion onto topic of this thread: Although this El Nino is a super-strength El Nino it is arguably no stronger than 1998 or 1983. I've seen no evidence that El Ninos are becoming more frequent. This only leaves El Ninos becoming longer: Since 2014 was predictied to be a El Nino year and spent a long time in almost El Nino conditions this would give some evidence that El Ninos are becoming longer. It would also suggest that if there is to be any variance from past behaviour in the latter stages of this El Nino then it will more likely be a lengthening of the transition to neutral conditions. Any thoughts?
I am running out of time to address the questions that you raise, so I point you to the 2015, and 2014, El Nino? threads linked below, and I provide a few selected extracts.
In summary, the question of whether global warming will result in more frequent, and/or stronger, El Ninos, is still under discussion, but I believe that that this discussion is leaning in favor of a "yes" answer. Observations of the non-proxy record of Super El Ninos is relatively sparse so it is hard to say with certainty, but I lean in favor of erring on the side of human safety and assuming that it is true that global warming will result in both more frequent and larger El Ninos; which by default means that climate sensitivity is higher than the IPCC commonly assumes. Certainly, if the NDJ, and/or the DJF, ONI index is at, or above, 2.5 for our current 15-16 event, then I would say that this evidence tends to support my position.
For 2015 see:http://forum.arctic-sea-ice.net/index.php/topic,1064.0.html
The following linked reference provides some more insights on the growing ENSO risks with continued global warming; however, it concludes with a call for still further research on this complex matter:
Wenju Cai, Agus Santoso, Guojian Wang, Sang-Wook Yeh, Soon-Il An, Kim M. Cobb, Mat Collins, Eric Guilyardi, Fei-Fei Jin, Jong-Seong Kug, Matthieu Lengaigne, Michael J. McPhaden, Ken Takahashi, Axel Timmermann, Gabriel Vecchi, Masahiro Watanabe & Lixin Wu (2015), "ENSO and greenhouse warming", Nature Climate Change, Volume: 5, Pages: 849–859, doi:10.1038/nclimate2743http://www.nature.com/nclimate/journal/v5/n9/full/nclimate2743.html
Abstract: "The El Niño/Southern Oscillation (ENSO) is the dominant climate phenomenon affecting extreme weather conditions worldwide. Its response to greenhouse warming has challenged scientists for decades, despite model agreement on projected changes in mean state. Recent studies have provided new insights into the elusive links between changes in ENSO and in the mean state of the Pacific climate. The projected slow-down in Walker circulation is expected to weaken equatorial Pacific Ocean currents, boosting the occurrences of eastward-propagating warm surface anomalies that characterize observed extreme El Niño events. Accelerated equatorial Pacific warming, particularly in the east, is expected to induce extreme rainfall in the eastern equatorial Pacific and extreme equatorward swings of the Pacific convergence zones, both of which are features of extreme El Niño. The frequency of extreme La Niña is also expected to increase in response to more extreme El Niños, an accelerated maritime continent warming and surface-intensified ocean warming. ENSO-related catastrophic weather events are thus likely to occur more frequently with unabated greenhouse-gas emissions. But model biases and recent observed strengthening of the Walker circulation highlight the need for further testing as new models, observations and insights become available."
For 2014 see:http://forum.arctic-sea-ice.net/index.php/topic,730.0.html
Furthermore, the following linked reference indicates that before 2040 CMIP5 models indicate that the amplitude of the ENSO phases will increase due to global warming:
Seon Tae Kim, Wenju Cai, Fei-Fei Jin, Agus Santoso, Lixin Wu, Eric Guilyardi & Soon-Il An, (2014), "Response of El Niño sea surface temperature variability to greenhouse warming", Nature Climate Change, doi:10.1038/nclimate2326http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2326.html
Abstract: "The destructive environmental and socio-economic impacts of the El Niño/Southern Oscillation (ENSO) demand an improved understanding of how ENSO will change under future greenhouse warming. Robust projected changes in certain aspects of ENSO have been recently established. However, there is as yet no consensus on the change in the magnitude of the associated sea surface temperature (SST) variability, commonly used to represent ENSO amplitude, despite its strong effects on marine ecosystems and rainfall worldwide. Here we show that the response of ENSO SST amplitude is time-varying, with an increasing trend in ENSO amplitude before 2040, followed by a decreasing trend thereafter. We attribute the previous lack of consensus to an expectation that the trend in ENSO amplitude over the entire twenty-first century is unidirectional, and to unrealistic model dynamics of tropical Pacific SST variability. We examine these complex processes across 22 models in the Coupled Model Intercomparison Project phase 5 (CMIP5) database, forced under historical and greenhouse warming conditions. The nine most realistic models identified show a strong consensus on the time-varying response and reveal that the non-unidirectional behaviour is linked to a longitudinal difference in the surface warming rate across the Indo-Pacific basin. Our results carry important implications for climate projections and climate adaptation pathways."
The following two abstracts from the 2014 Ocean Sciences Meetings, in February 2014 in Hawaii clearly supports the conclusion that due to global warming we can expect to experience more frequent strong El Nino events, both now and in the future:
"MORE FREQUENT EMERGENCE OF EL NIÑO PROPAGATION ASYMMETRY DUE TO GREENHOUSE WARMING
Sea surface temperature anomalies typically propagate westward along the equatorial Pacific during both El Niño and La Niña events. Since the late 1970’s however, an opposite propagation has been observed, most prominently during extreme El Niño events. This propagation asymmetry challenges existing theories on how ENSO works. Through heat budget analysis utilising various observational data assimilation systems, the equatorial Pacific currents are found to be an important element for this asymmetry, whereby the westward flowing currents are enhanced during La Niña but reversed during extreme El Niño events. Our results highlight that propagation asymmetry is favoured when the westward mean currents weaken. By analysing climate models that participated in the Coupled Model Intercomparison Project phases 3 and 5, it is found that as the mean currents weaken under global warming, an aggregate of models with more realistic propagation behaviour indeed simulate a doubling in the frequency of eastward propagating El Niños. Our results have implications for understanding ENSO behaviour across models, and suggest that more frequent emergence of eastward El Niño will be a symptom of a warming climate."
Santoso, A., University of New South Wales, Australia, firstname.lastname@example.org
McGregor, S., University of New South Wales, Australia, email@example.com
Jin, F. F., University of Hawaii, USA, firstname.lastname@example.org
Cai, W., CSIRO, Australia, email@example.com
England, M. H., University of New South Wales, Australia, firstname.lastname@example.org
"INFERRED CHANGES IN EL NIÑO-SOUTHERN OSCILLATION VARIANCE OVER THE PAST SIX CENTURIES
It is vital to understand how the El Niño–Southern Oscillation (ENSO) has responded to past changes in natural and anthropogenic forcings, in order to better understand and predict its response to future greenhouse warming. To date, however, the instrumental record is too brief to fully characterize natural ENSO variability, while large discrepancies exist amongst paleo-proxy reconstructions of ENSO. These paleo-proxy reconstructions have typically attempted to reconstruct ENSO’s temporal evolution, rather than the variance of these temporal changes. Here a new approach is developed that synthesizes the variance changes from various proxy datasets to provide a unified and updated estimate of past ENSO variance. The method is tested using surrogate data from two coupled general circulation model (CGCM) simulations. It is shown that in the presence of dating uncertainties, synthesizing variance information provides a more robust estimate of ENSO variance than synthesizing the raw data and then identifying its running variance. Synthesizing existing ENSO reconstructions to arrive at a better estimate of past ENSO variance changes, we find robust evidence that the ENSO variance for any 30-year period during the interval 1590-1880 was considerably lower than that observed during 1979-2009."
McGregor, S., Climate Change Research Centre, UNSW, Australia, email@example.com
Timmermann, A., IPRC, University of Hawaii, USA, firstname.lastname@example.org
England, M. H., Climate Change Research Centre, UNSW, Australia, email@example.com
Elison Timm, O., University at Albany, State University of New York, USA, firstname.lastname@example.org
Wittenberg, A. T., GFDL, NOAA, USA, email@example.com
The linked reference indicates that following a RCP 8.5 scenario will result in a tripling of the frequency of extreme positive IOP events, indicates that extreme El Nino events will also become more frequent in the future:
Wenju Cai, Agus Santoso, Guojian Wang, Evan Weller, Lixin Wu, Karumuri Ashok, Yukio Masumoto & Toshio Yamagata, (2014), "Increased frequency of extreme Indian Ocean Dipole events due to greenhouse warming", Nature, 510,254–258, doi:10.1038/nature13327http://www.nature.com/nature/journal/v510/n7504/full/nature13327.html
Abstract: "The Indian Ocean dipole is a prominent mode of coupled ocean–atmosphere variability, affecting the lives of millions of people in Indian Ocean rim countries. In its positive phase, sea surface temperatures are lower than normal off the Sumatra–Java coast, but higher in the western tropical Indian Ocean. During the extreme positive-IOD (pIOD) events of 1961, 1994 and 1997, the eastern cooling strengthened and extended westward along the equatorial Indian Ocean through strong reversal of both the mean westerly winds and the associated eastward-flowing upper ocean currents. This created anomalously dry conditions from the eastern to the central Indian Ocean along the Equator and atmospheric convergence farther west, leading to catastrophic floods in eastern tropical African countries but devastating droughts in eastern Indian Ocean rim countries. Despite these serious consequences, the response of pIOD events to greenhouse warming is unknown. Here, using an ensemble of climate models forced by a scenario of high greenhouse gas emissions (Representative Concentration Pathway 8.5), we project that the frequency of extreme pIOD events will increase by almost a factor of three, from one event every 17.3 years over the twentieth century to one event every 6.3 years over the twenty-first century. We find that a mean state change—with weakening of both equatorial westerly winds and eastward oceanic currents in association with a faster warming in the western than the eastern equatorial Indian Ocean—facilitates more frequent occurrences of wind and oceanic current reversal. This leads to more frequent extreme pIOD events, suggesting an increasing frequency of extreme climate and weather events in regions affected by the pIOD."