Super El Niños Becoming More Frequent As Climate Warms

[bluewave]

https://www.pnas.org/content/early/2019/10/15/1911130116

          PNAS first published October 21, 2019

Significance

How the magnitude of El Niño will change is of great societal concern, yet it remains largely unknown. Here we show analysis of how changing El Niño properties, due to 20th century climate change, can shed light on changes to the intensity of El Niño in the future. Since the 1970s, El Niño has changed its origination from the eastern Pacific to the western Pacific, along with increased strong El Niño events due to a background warming in the western Pacific warm pool. This suggests the controlling factors that may lead to increased extreme El Niño events in the future. If the observed background changes continue under future anthropogenic forcing, more frequent extreme El Niño events will induce profound socioeconomic consequences.

Abstract

El Niño’s intensity change under anthropogenic warming is of great importance to society, yet current climate models’ projections remain largely uncertain. The current classification of El Niño does not distinguish the strong from the moderate El Niño events, making it difficult to project future change of El Niño’s intensity. Here we classify 33 El Niño events from 1901 to 2017 by cluster analysis of the onset and amplification processes, and the resultant 4 types of El Niño distinguish the strong from the moderate events and the onset from successive events. The 3 categories of El Niño onset exhibit distinct development mechanisms. We find El Niño onset regime has changed from eastern Pacific origin to western Pacific origin with more frequent occurrence of extreme events since the 1970s. This regime change is hypothesized to arise from a background warming in the western Pacific and the associated increased zonal and vertical sea-surface temperature (SST) gradients in the equatorial central Pacific, which reveals a controlling factor that could lead to increased extreme El Niño events in the future. The Coupled Model Intercomparison Project phase 5 (CMIP5) models’ projections demonstrate that both the frequency and intensity of the strong El Niño events will increase significantly if the projected central Pacific zonal SST gradients become enhanced. If the currently observed background changes continue under future anthropogenic forcing, more frequent strong El Niño events are anticipated. The models’ uncertainty in the projected equatorial zonal SST gradients, however, remains a major roadblock for faithful prediction of El Niño’s future changes.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083906?af=R

  First published: 25 October 2019

Abstract

The El Niño‐Southern Oscillation (ENSO) represents the largest source of year‐to‐year global climate variability. While earth system models suggest a range of possible shifts in ENSO properties under continued greenhouse gas forcing, many centuries of preindustrial climate data are required to detect a potential shift in the properties of recent ENSO extremes. Here, we reconstruct the strength of ENSO variations over the last 7,000 years with a new ensemble of fossil coral oxygen isotope records from the Line Islands, located in the central equatorial Pacific. The corals document a significant decrease in ENSO variance of ~20% from 3,000 to 5,000 years ago, coinciding with changes in spring/fall precessional insolation. We find that ENSO variability over the last five decades is ~25% stronger than during the preindustrial. Our results provide empirical support for recent climate model projections showing an intensification of ENSO extremes under greenhouse forcing.

Plain Language Summary

Recent modeling studies suggest El Niño will intensify due to greenhouse warming. Here, new coral reconstructions of the El Niño‐Southern Oscillation (ENSO) record sustained, significant changes in ENSO variability over the last 7,000yrs, and imply that ENSO extremes of the last 50 years are significantly stronger than those of the pre‐industrial era in the central tropical Pacific. These records suggest that El Niño events already may be intensifying due to anthropogenic climate change.

Key Points

 

• Line Island corals provide 1,751 years of monthly‐resolved ENSO variability from the mid‐Holocene to present
• ENSO strength is significantly weaker between 3,000 and 5,000 years ago compared to the 2,000‐year periods both before and after
• ENSO extremes of the last 50 years are significantly stronger than those of the pre‐industrial era in the central tropical Pacific

 

 

 

 

        

          
 
 

 

 

 

 

 

[raindancewx]

This is why I always argue ENSO events should be defined against a long-term, stable period. I use 1951-2010. CPC adjusts the baseline for El Nino and La Nina every five years, as if there is some law of the universe that says we have to have a 30-40-30 split between El Nino/Neutral/La Nina. I think its pretty likely that we're moving to a state where El Nino is the most likely outcome of the three, even recognizing that the PDO base state has some say in ENSO frequency historically.

Also, a lot of the effects that are supposed to be canonical to the three states really have to do with ENSO order more than anything. I think the tendency for the West will be more warm/wet winters generally, but the increasing likelihood of El Nino means that when we do see harsh winters - generally El Ninos after La Ninas - they will be fierce, like 2018.

[LibertyBell]

On 10/29/2019 at 9:10 PM, raindancewx said:

This is why I always argue ENSO events should be defined against a long-term, stable period. I use 1951-2010. CPC adjusts the baseline for El Nino and La Nina every five years, as if there is some law of the universe that says we have to have a 30-40-30 split between El Nino/Neutral/La Nina. I think its pretty likely that we're moving to a state where El Nino is the most likely outcome of the three, even recognizing that the PDO base state has some say in ENSO frequency historically.

Also, a lot of the effects that are supposed to be canonical to the three states really have to do with ENSO order more than anything. I think the tendency for the West will be more warm/wet winters generally, but the increasing likelihood of El Nino means that when we do see harsh winters - generally El Ninos after La Ninas - they will be fierce, like 2018.

California has been having a lot of dry winters even during el ninos.

 

[raindancewx]

Not really. Most of the recent El Ninos have been good for at least parts of California for moisture. Without looking, I think maybe 2014 and 2002 are the exceptions since 1997. 

[LibertyBell]

On 11/1/2019 at 7:19 PM, raindancewx said:

Not really. Most of the recent El Ninos have been good for at least parts of California for moisture. Without looking, I think maybe 2014 and 2002 are the exceptions since 1997. 

Yep 2014 was the one which disappointed.  I thought 2015 wasn't that good there either?

 

[raindancewx]

California largely ended its drought from the 2015-16 El Nino favoring the North for snow, and then the 2016-17 La Nina producing a lot of storminess in Nov/Jan/Apr throughout the SW. The 2018-19 winter was better than 2016-17 in the SW for snow-pack, but not due to moisture - it just didn't melt quickly because it was far colder in Spring.