by Judith Curry
All eyes are on the tropical Pacific Ocean
El Nino events have major impacts on weather in many regions across the globe. Californians are hoping for an El Nino to end their drought. Many climate scientists are also hoping for an El Nino to put an end to that pesky ‘pause’. So what are the prospects for an El Nino in the coming year?
The following signals in the observations portend an El Nino this summer:
- Increased warming in the central and eastern tropical Pacific Ocean
- Positive thermocline slope index (between the western and eastern Pacific)
- Westerly wind bursts and Kelvin waves helping to push the warm water eastward.
Background information on El Nino and how it is forecast is provided at:
What the experts say
for a comprehensive list of forecast pages for El Nino.
The Australian Bureau of Meteorology estimates a 70% chance of developing an El Nino during SH winter (NH summer), in a brief
issued April 8.
The US NOAA Climate Prediction Center issued a new report
today, stating that the chances of El Nino exceed 50% by summer. The NOAA Report is very informative.
Several experts quoted in the media are more bullish than the NOAA forecast.
Spring ENSO predictability barrier
ENSO forecasts issued in spring are highly uncertain, owing to the so-called springtime predictability barrier. The canonical paper on the spring predictability barrier is a paper by Peter Webster entitled Monsoon and ENSO: Selectively Interactive Systems
Since this paper was published, coupled seasonal forecast models have improved, but this springtime predictability barrier remains, see this paper by Kim, Webster and Curry: Impact of Shifting Patterns of Pacific Ocean Warming on North Atlantic Tropical Cyclones
, especially Fig 3 and the associated discussion. The punchline is that for ECMWF System 4 seasonal forecasts initiated April 1, forecasts of tropical eastern Pacific surface temperatures (NINO3) rapidly lose skill, whereas forecasts for central Pacific surface temperatures (NINO4) retain skill out for 6 months. Forecasts initiated June 1 retain their skill out to 6 months, for both NINO3 and NINO4.
Seasonal forecast models (see the NOAA report for a summary) predict an El Nino for summer, perhaps starting as early as May. Here are the ECMWF forecasts, initialized April 1:
A recent example of a fizzled El Nino forecast was summer of 2012; there was only the barest hint of an El Nino during summer, and then it fizzled out.
Super El Nino?
Some scientists are predicting a super El Nino, such as seen during 1997/1998, and 1982. Mashable has two posts on this [here
] and [here
Both of these two super El Nino events occurred during the warm phase of the PDO. During the cool phase of the PDO (which we are currently in), overall the El Nino events are less frequent and of lower magnitude. The strongest El Nino in a previous cool phase of the PDO was in 1972/1973.
Apart from the difficulty of predicting the occurrence of an El Nino, predicting the strength and duration is even more difficult.
Which flavor of El Nino?
The impacts of an El Nino vary substantially with its ‘flavor’, i.e. whether the warming is concentrated in the East Pacific (NINO3), Central Pacific (El Nino Modoki; NINO4), or mixed. These impacts include tropical cyclone intensity and frequency [link
] and [link
], and drought and rainfall patterns. For example, for a regular El Nino in the easter Pacific, California will get plenty of rain in the winter. However, this is not the case for a Modoki El Nino, where warming is in the Central Pacific. Look at the ECMWF forecasts above; there is a hint that towards winter, the Modoki could be dominant with a mixed El Nino type, with little rain in California.
Joe Romm is clearly looking for a Super El Nino to shatter global temperature records [link]. The 1998 El Nino clearly had a very large warming effect on global surface and atmospheric temperatures. The 1982 and 1972/1973 El Nino events did not have much a an impact on global temperatures (although 1982 coincided with the eruption of El Chichon).
A new paper provides some insight into this issue:
The influence of different El Nino types on global average temperature
Sandra Banholzer and Simon Donner
Abstract. The El Niño/ Southern Oscillation (ENSO) is known to influence surface temperatures worldwide. El Niño conditions are thought to lead to anomalously warm global average surface temperature, absent other forcings. Recent research has identified distinct possible types of El Niño events based on the location of peak sea surface temperature anomalies. Here we analyze the relationship between the type of El Niño event and the global average temperature anomaly, using three historical temperature datasets. Separating El Niño events into types reveals that the global average surface temperatures are anomalously warm during and after traditional Eastern Pacific El Niño events, but not Central Pacific or Mixed events. Historical analysis indicated that slowdowns in the rate of global surface warming since the late-1800s may be related to decadal variability in the frequency of different types of El Niño events.
Published online J. Geophysical Research [link to abstract]
So will a 2014/2015 be a pause buster? Probably not, given that we are in the cool phase of the PDO.
It is likely that we will see an El Nino this summer. However, the intensity, duration and ‘flavor’ are uncertain at this point. In any event, we stand to learn something from whatever transpires. If I am allowed to ‘hope’ for anything, I hope that there will be regular El Nino conditions next winter so that Californians will get some rain.
With regards to the pause, I don’t see a pause buster given that we are in the cool phase of the PDO.
Time will tell.