An El Niño appears increasingly likely this year, according to the National Oceanic and Atmospheric Administration (NOAA) and Australia’s Bureau of Meteorology (BOM). If it starts relatively quickly, then 2014 could well be the hottest year on record, but if it is a strong El Niño, as many currently expect, then 2015 would likely break all previous global records.

The BOM’s biweekly ENSO (El Niño Southern Oscillation) Wrap-Up begins:

The likelihood of El Niño remains high, with all climate models surveyed by the Bureau now indicating El Niño is likely to occur in 2014. Six of the seven models suggest El Niño thresholds may be exceeded as early as July.

The latest weekly ENSO report from NOAA’s National Centers for Environmental Prediction (NCEP) puts the chances of an El Niño by the end of the year at almost 2 out of 3:

 

ENSO 4-22

An El Niño is marked by unusually warm ocean temperatures for a period of several months in the Equatorial Pacific, as I discussed in March. In contrast, a La Niña has cooler than normal temps in the same region. Both tend to drive extreme weather worldwide.

The following chart from NASA shows that El Niños are generally the hottest years on record — since the regional warming adds to the underlying man-made global trend — whereas La Niña years are usually below the global warming trend line.

 

temperature anomalies

Chart of global temperature since 1950, also showing the phase of the El Niño-La Niña cycle. Via NASA.

The El Niño event of 1997-1998 “was so powerful, it created a +0.2 degrees Celsius temperature anomaly (on top of the 30-year average trend),” as BitsOfScience pointed out earlier this month. That event “started somewhere in May of 1997 and ended almost a full year later, around April 1998. Globally 1997 indeed turned out to be relatively warm (>0.05C above average)” but 1998 was nearly four times as hot.

When the El Niño forms and then peaks is crucial to whether 2014 or 2015 (or both) will be the hottest year on record. A 2010 NASA study found the 12-month running-mean global temperature tends to lag the temperature in the key Niño 3.4 region of the equatorial Pacific “by 4 months.”

Because 1997/1998 was a “super El Niño,” and because we haven’t had one of those since — or indeed any El Niño at all since 2010 — it can appear as if global warming has slowed (if you cherry-pick a relatively recent start year). But in fact several recent studies have confirmed that planetary warming continues apace everywhere you look, especially the ocean.

Recent research finds that one reason the rate of surface warming has the slowed down is that trade winds have sped up in an unprecedented fashion, mixing more heat deeper into the oceans, while bringing cooler water up to the surface. Remember, more than 90 percent of human-induced planetary warming goes into the oceans, while only 2 percent goes into the atmosphere, so small changes in ocean uptake can have huge impact on surface temperatures. The lead author of this study explained when that process ends “as it inevitably will –- our research suggests heat will quickly accumulate in the atmosphere. So global temperatures look set to rise rapidly.”

As meteorologist Eric Holthaus notes on Slate, a major El Niño could in fact be the triggering event to the return of the rapid phase of warming surface air temperatures.

In that regard, it’s worth noting that as of this week, “With the ever-more certain approach of El Nino, the world ocean surface is starting to radiate more and more heat.” In fact, “temperatures had spiked to an extraordinary +1.12 C hotter than ‘normal’ for the entire global ocean system.”

Since this El Niño could be the defining climate event for the next few years, Climate Progress will be reporting on it regularly.

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