In the masterfully constructed fantasy world of Westeros, George R.R. Martin’s characters have a saying — Winter is Coming.
The words are spoken with an air of dread as winters in this realm can extend for years, starve entire cities, and push civilizations to the brink. In a world impacted by human climate change, the words El Nino might be uttered with a similar dread, as it foreshadows a dumping of Pacific Ocean heat back into an already warming atmosphere.
The result is that most moderate to strong El Nino years are record hot years, pushing the global temperature average ever higher through a cycle of natural variability warped toward hot by human greenhouse gas forcing. And, in fact, even two of the recent weak El Nina years, 2005 and 2010, were both hottest years on record:
(NASA GISS temperature graph showing global increases since 1950 reflecting El Nino, La Nina, and ENSO neutral years. Image source: NASA GISS.)
These new record high temperatures occurred during a period when cold water upwelling in the Pacific was particularly strong. Driven by the most powerful trade winds on record, this ocean surface and atmosphere mixing dumped an unprecedented amount of heat into Pacific waters. It is a period known as negative Pacific Decadal Oscillation and it usually reflects a time of cooling for the atmosphere. But, despite this rather intense period of heat transfer from atmosphere to ocean, the atmosphere remained at or near record hot levels, only slightly slowing in its rate of upward rise.
El Nino is Coming
Now, according to reports from NOAA, the waters just below the surface of the Eastern Pacific are starting to warm and rise. This warm water pulse, known as a Kelvin Wave, is proceeding from west to east even as it is rising from the depths. The source of these warm waters is a deep, hot pool in the Central and Western Pacific. A pool of warmth that has been intensified over the last 14 years by a near constant bombardment of above normal ocean surface temperatures. The hot ocean waters evaporated, becoming more heavily burdened with saline and eventually sank far into the depths.
Now, as the trade winds have weakened and westerlies sporadically began to emerge, this pool of hot water was drawn eastward by upwelling currents near the South American Continent. Should these hotter waters break the surface, the world will experience a moderate to strong El Nino along with global atmospheric temperatures that are likely to be the hottest on record.
From the NOAA ENSO forecast:
While all models predict warming in the tropical Pacific, there is considerable uncertainty as to whether El Niño will develop during the summer or fall. If westerly winds continue to emerge in the western equatorial Pacific, the development of El Niño would become more likely. However, the lower forecast skill during the spring and overall propensity for cooler conditions over the last decade still justify significant probabilities for ENSO-neutral. The consensus forecast is for ENSO-neutral to continue through the Northern Hemisphere spring 2014, with about a 50% chance of El Niño developing during the summer or fall.
Meanwhile, the latest Climate Prediction Center forecast now shows a 52% chance that El Nino will form by the months of October, November and December:
(CPC ENSO forecast through December of 2014. Image source: IRI CPC)
This is slight increase of about 2% from even the late February analysis.
It’s worth noting that though continued forecast agreement across agencies through early March provides increased likelihood of El Nino’s emergence later this year, spring forecasts are typically somewhat unreliable due to atmospheric instability. In addition, the Pacific Ocean remaining in a negative PDO state over the last 14 years also produces some uncertainty in the forecast.
“Impressive” Subsurface Warming
In addition to models showing an increased chance of El Nino starting in April and rising through November, projections imply that this El Nino, should it emerge, may be the strongest in over a decade. As noted above, a very large pool of warm water is rising up from the depths. Meanwhile, model runs show sea surface temperatures warming to an average deviation above 1.25 degrees Celsius with some showing values above 2.5 C. Such moderate to strong values, should they emerge, could produce the warmest conditions for the Eastern Pacific since 1998, a powerful event that spiked surface water temperatures for that region up to 2.9 C above normal.
(Strong Kelvin Wave spreads eastward and features subsurface temperature anomalies in the range of 4-6 C above average in a wide zone at 150 depth. Note the wave beginning to push above 60 meters in a region near the Eastern Pacific during late February. Image source: NOAA.)
Mark Halpert, acting director at the Climate Prediction Center, noted that subsurface warming was “impressive” and seemed quite confident for early spring that this region of the world was developing toward a substantial El Nino event later this year.
Globe to Warm. Amped Hydrological Cycle, Sea Ice Loss to Play a Role in El Nino Induced Weather Swings?
Should the predicted El Nino emerge and be as strong as average model values indicate, global surface temperatures could rise by between .05 and .15 degrees Celsius, pushing climatology into a range of .85 to .95 degrees Celsius above 1880s values. This would be a substantial jump for a single year, resulting in yet one more large shift toward an ever more extreme climate.
Perhaps also as concerning is the fact that El Nino often results in severe weather shifts around the globe. With drought and flood events already being amplified by a 6% increase in the hydrological cycle since 1880 and with a massive reduction in Arctic sea ice coverage playing havoc with the Jet Stream, adding an excess of heat over hundreds of thousands of square miles of Eastern Pacific waters is likely to further increase instability.
As examples, the last, rather mild, El Nino of 2010 coincided with one of the worst heatwaves and wildfire outbreaks ever experienced in Russia, while the powerful 1998 El Nino battered California with a winter-long series of extraordinarily intense storms.
(El Nino flattens and amplifies storm track while aiming it at the US West Coast. In combination with already excessive atmospheric moisture levels driven by human-caused warming, such a situation can result in an extraordinarily extreme progression of storms for California in the event that a strong El Nino combines with human-warming driven weather alterations. Image source: ZoomRadar.)
For the potentially arising El Nino, farmers in California may experience a switch from extreme drought conditions to extreme deluge. The result of a flattening pattern in the Pacific Jet Stream that tends to coincide with El Nino to funnel a river of Pacific moisture directly over the US West Coast. With the hydrological cycle already amped up by human-caused warming, such a large moisture dump could be even worse than those previously experienced.
As observed in 2010, high temperature anomalies over Central Asia that typically coincide with El Nino can, in the current climate state, result in severe droughts and wildfire outbreaks. This could result in an expanding zone of drought and fire as well as produce a troubling hot air pool that could occasionally spill into the Arctic. If the pattern emerges during summer or early fall, the result could be both record sea ice melt and severe heatwaves, wildfires and droughts from the center of the Eurasian Continent all the way to the Arctic Ocean.
It’s worth noting that both increased rates of evaporation and very low levels of Arctic sea ice could amplify some aspects of El Nino induced weather extremes. So the combination of spiking global temperatures and adding yet more weather instability to an already amped up system could make a moderate to strong 2014 El Nino a severe event indeed.