The Eastern U.S. and the Caribbean could see less threat from hurricanes this fall — as the Pacific Coast sees more.
Those are just two possible ramifications if the tropical Pacific slips back into the warmer half of a key climatic pattern — something that seems likely, according to the World Meteorological Organization.
The U.N. agency announced Thursday that a reversal in the El Niño Southern Oscillation (ENSO) was about 80 percent likely by September.
The tropical Pacific is currently in the neutral part of that pattern. A return to the “warmer” El Niño half of the pattern — which happens every three to seven years — would “most likely lead to a new spike in global heating and increase the chance of breaking temperature records,” WMO Secretary-General Petteri Taalas said in a statement.
It also meant a reversal of the now-departed (and cooler) La Niña part of the pattern, which had “acted as a temporary brake on global temperature increase,” Taalas said.
But it is complicated to connect between something as big as a global annual mean temperature and specific on-the-ground weather.
While the odds are that global average temperatures will increase under El Niño conditions, “we don’t live in global mean temperatures,” said Michelle L’Heureux, a meteorologist with the Climate Prediction Center at the National Weather Service (NWS).
For the United States, any heat impacts are likely to be less dramatic than elsewhere, L’Heureux said — because peak heating effects in the U.S. come in winter.
Roughly speaking, the impacts of the El Niño on the jet stream will lead to colder conditions in the southern part of the country; wetter conditions across the West; and a dryer, warmer winter for the northern states.
That could broadly mean more chance of ice and snow in the southern U.S., and less chance in the North.
However, those patterns could simply get swallowed up against the greater rise of temperatures due to climate change. “Because climate change is so potent, it tends to override that signal,” L’Heureux said.
It also could mean fewer hurricanes hitting the Caribbean and East Coast. The switch of the ENSO pattern in the Pacific leads — by a circuitous atmospheric path across the gyres of North America — to the rise of powerful vertical winds in the Gulf and Atlantic.
Those winds can pull hurricanes apart before they can form into a stable horizontal cyclone, decreasing the chance of hurricanes.
The announcement from the WMO follows prior warnings from the U.S. National Weather Service that Niño conditions were about two-thirds likely between May and July.
Even if the El Niño develops, it would still take months for it to reach the United States — with peak effects likely arriving by the winter of 2023 or spring of 2024.
Assuming that it arrives at all, which is by no means guaranteed.
Starting in the spring, L’Heureux begins combing the tropical Pacific for evidence of the wind anomalies and rising ocean temperatures that could signal a burgeoning El Niño.
That’s inherently “anxiety inducing,” she wrote in a blog post Thursday, because El Niño isn’t an event but the lengthy, subtle emergence of a larger pattern out of more ambiguous conditions, like wind directions and changing ocean temperatures.
A developing El Niño requires a hotter tropical Pacific — but while that’s a necessary condition, heat won’t create the pattern on its own. There also has to be a lengthy east-blowing wind anomaly, which pulls against the usually west-blowing trade winds of the Pacific.
Those wind anomalies are present at a “low level” this year, NWS announced in April. But sometimes they fizzle out before summer, as happened before the “potentially major” El Niño event of 2014, L’Heureux wrote.
Even if El Niño does appear this summer, it will be winter or early spring before it begins to change conditions in the U.S., L’Heureux told The Hill.
The U.S. government tracks it so early because El Niño (or La Niña, for that matter) stacks the deck toward weather anomalies later in the year.
By watching the Pacific for signs of El Niño, “we’re often informed earlier than when the peak impacts occur, and we start tilting the given probabilities of outcomes and impacts over the United States,” L’Heureux said.
Being able to account for that noise helps make predictions on the whole more accurate. But on the individual scale, the subtle impacts of El Niño are often swallowed by both the background pattern of climate change, and the wilder noise of day-to-day weather.
The ENSO warming pattern is also distinct from the broader pattern of climate change, and the two sometimes mute each other — and sometimes they overlap.
In 2016, for example, the world saw its hottest summer on record, leading to deadly heat waves — the result of what the WMO called Thursday a “double whammy” of El Niño and climate change.
The increased average temperatures during El Niño is in part a bookkeeping error.
Because the Pacific Ocean is so large, a rise in temperature across much of its area has an outsized impact on the global average, even though it doesn’t actually represent additional heat entering the Earth system — just heat that was in the atmosphere getting moved into the ocean, according to an FAQ from Climate.gov.
“The whole climate system isn’t really cooling or warming. Heat energy that’s already present in the climate system is simply shifting back and forth between the atmosphere (where it shows up in the global surface temperature value) and the deeper layers of the ocean (where it doesn’t),” according to the fact sheet.