By Andrea Thompson
Every month since March, when the first El Niño Watch was issued, forecasters, government officials around the world, and yes, even those in the media, have been watching with bated breath to see whether various climate agencies would officially pronounce the arrival of that infamous climate phenomenon. So far, no clear-cut El Niño has been declared, but that hasn’t stopped the continual updates and dissections of the most recent seasonal forecasts and trends in ocean temperatures and winds, as if they were the latest juicy plot twist on “Scandal” or “Game of Thrones.”
If you aren’t among those obsessively tracking Kelvin waves and the Nino3.4 region — and the next “official” update is expected on Aug. 7 — you may wonder what all the fuss is about. After all, El Niño is just the warming of ocean waters in the tropical Pacific. So why the heck do we care so much about it?
We care because this seemingly isolated event is just one part of the global climate system and can actually have major influences on the weather and climate around the world, from the U.S. to Australia to eastern Africa. For example, El Niño shifts atmospheric patterns in a way that typically brings more rain to the southern U.S., but drought to Indonesia. Those changes can, in turn, have economic and health consequences, such as altering the crop yields in agricultural markets or providing a more conducive environment for the spread of malaria. Because of these impacts, groups at the U.S. National Centers for Environmental Prediction, or NCEP (which is part of the National Oceanic and Atmospheric Administration), the Australian Bureau of Meteorology, and other organizations around the world watch the changing conditions in the Pacific Ocean and make forecasts for whether and when an El Niño might develop.
El Niño also leads to warmer average global temperatures, which come atop the underlying trend of rising temperatures spurred by global warming. The only year in the top 10 warmest globally that wasn’t during the 21st century was 1998, when one of the strongest El Niños on record was in force.
Not all of El Niño’s effects are negative: The atmospheric changes it spurs tend to tamp down on tropical cyclones and hurricanes in the Atlantic Ocean basin, something denizens of the Caribbean and Gulf and East coasts of the U.S. surely appreciate.
“In an El Niño year, you have winners and losers,” Walter Baethgen, a senior research scientist with the International Research Institute for Climate and Society at Columbia University’s Earth Institute, said in an IRI video.
Exactly what impacts are seen and when they emerge can the timing of an El Niño — the current event is expected to emerge late this summer or early in the fall. But even while one is building, it can still influence weather conditions, as this event seems to be doing. The strength that a full-blown El Niño achieves can also affect the impacts it brings — for example, the excess rains that parched California so desperately needs seem only to be a feature of a strong El Niño.
“There is a lot of variety in exactly how strong they get, exactly what month they begin, or are identified as El Niño events, as well as the exact month in which they peak,” said IRI director Lisa Goddard during a press call held by the climate communication group Climate Nexus. “So all of these differences can influence (El Niño’s) regional climate impacts.”
What Is El Niño?
El Niño is a cyclical climate phenomenon that occurs every 3 to 5 years (though that return period can be as short as 2 and as long as 7 years). It’s defining characteristic is the buildup of warmer-than-normal surface waters over the eastern and central tropical Pacific Ocean. (This warm phase is part of a larger cycle called the El Niño-Southern Oscillation that also has a neutral phase and a cold phase, called La Niña.)
These warmer waters are linked to — or coupled with, as atmospheric scientists say — changes in the winds over the region. In neutral conditions, these winds blow from east to west across the basin, piling up the warm water in the western portion of the basin, near Indonesia. But during El Niño, the winds relax, and the warm water slides back east, like a ball rolling down a hill.
The warm water fuels thunderstorms in the atmosphere overhead, which in turn warms the atmosphere through a process called latent heating. The shift in where the warm water is and the increase in the heat the ocean releases cause a shift in this storminess and heating, which affects one of the main circulations of the atmosphere, the Hadley circulation. The Hadley circulation features air rising near the equator and traveling toward higher latitudes where it sinks and flows back to the equator. The increased heat from El Niño turbocharges the poleward flow, which in turn causes further changes in atmospheric flow, including to the jet stream over the Pacific.
“The phenomenon itself is specific to the tropical Pacific, even though it does have worldwide impacts,” Goddard said during the press call.
While the atmospheric conditions with the current anticipated event haven’t yet shaped up to the point that NCEP and IRI forecasters are willing to officially declare an El Niño, they still place an 80 percent chance on one happening by late fall.
“It’s fairly confident, but it’s not a slam dunk,” Anthony Barnston, IRI’s chief forecaster, told Climate Central.
Not every place in the world is affected by El Niño, and not every El Niño produces the same effects as previous ones. But “there are places that have fairly reliable” climate effects, or teleconnections, Barnston said.
The most robust effects are precipitation-related. Both Indonesia and northern South America typically see below-normal rains that can lead to drought, while more rain is typically seen over southeastern South America, eastern equatorial Africa and the southern U.S.
The above-average rainfall in the southern U.S. is linked to the changes in the jet stream, as it tends to funnel more storms over the region.
There is interestingly one tiny area of northern South America, along the coasts of Ecuador and Peru, that actually sees increased rainfall. The rains are driven by the warmer waters just off the coast as they fuel storm activity. Such rains were actually seen earlier this spring when a particularly warm blob of water worked its way over to the eastern Pacific and fueled storms.
Not all of the changes linked to El Niño always occur: El Niño is linked to a less active monsoon over India, leading to drought conditions there, but this effect was missing during the 1997-1998 El Niño, one of the strongest on record. (The monsoon has been lackluster so far this year, but it’s unclear whether or not that’s related to the burgeoning El Niño, Barnston said.)