How El Nino could impact the world's weather in 2023-24
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[June 09, 2023]
By Gloria Dickie
LONDON(Reuters) - Countries are racing to prepare for extreme weather
later this year as the world tips into an El Nino — a natural climate
phenomenon that fuels tropical cyclones in the Pacific and boosts
rainfall and flood risk in parts of the Americas and elsewhere.
On Thursday, the U.S. National Oceanic and Atmospheric Administration
(NOAA) declared that an El Nino is now underway. The past three years
have been dominated by the cooler La Nina pattern.
Scientists say this year looks particularly worrying. The last time a
strong El Nino was in full swing, in 2016, the world saw its hottest
year on record. Meteorologists expect that this El Nino, coupled with
excess warming from climate change, will see the world grapple with
record-high temperatures.
Experts are also concerned about what is going on in the ocean. An El
Nino means that waters in the Eastern Pacific are warmer than usual. But
even before this El Nino began, in May, the average global sea surface
temperature was about 0.1C (0.2F) higher than any other on record. That
could supercharge extreme weather.
"We're in unprecedented territory," said Michelle L'Heureux, a
meteorologist with NOAA's Climate Prediction Center.
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This year's El Nino could lead to global economic losses of $3 trillion,
according to a study published last month in the journal Science,
shrinking GDP as extreme weather decimates agricultural production,
manufacturing, and helps spread disease.
Governments in vulnerable countries are taking note. Peru has set aside
$1.06 billion to deal with El Nino's impacts and climate change, while
the Philippines — at risk from cyclones — has formed a special
government team to handle the predicted fallout.
Here is how El Nino will unfold and some of the weather we might expect:
WHAT CAUSES AN EL NINO?
El Nino is a natural climate pattern borne out of unusually warm waters
in the eastern Pacific.
It forms when the trade winds blowing east-to-west along the equatorial
Pacific slow down or reverse as air pressure changes, although
scientists are not entirely sure what kicks off the cycle.
Because the trade winds affect the sun-warmed surface waters, a
weakening causes these warm western Pacific waters to slosh back into
the colder central and eastern Pacific basins.
During the 2015-16 El Nino — the strongest such event on record —
anchovy stocks off the coast of Peru crashed amid this warm water
incursion. And nearly a third of the corals on Australia's Great Barrier
Reef died. In too-warm waters corals will expel living algae, causing
them to calcify and turn white.
This build-up of warm water in the eastern Pacific also transfers heat
high into the atmosphere through convection, generating thunderstorms.
"When El Nino moves that warm water, it moves where thunderstorms
happen," said NOAA meteorologist Tom DiLiberto. "That's the first
atmospheric domino to fall."
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HOW DOES EL NINO AFFECT THE WORLD'S WEATHER?
This shift in storm activity affects the current of fast-flowing air
that moves weather around the world — called the subtropical jet
stream — pushing its path southward and straightening it out into a
flatter stream that delivers similar weather along the same
latitudes.
"If you're changing where the storm highway goes ... you're changing
what kind of weather we would expect to see," DiLiberto said.
During an El Nino, the southern United States experiences cooler and
wetter weather, while parts of the U.S. West and Canada are warmer
and drier.
Hurricane activity falters as the storms fail to form in the
Atlantic due to changes in the wind, sparing the United States. But
tropical cyclones in the Pacific get a boost, with storms often
spinning toward vulnerable islands.
Some parts of Central and South America experience heavy rainfall,
although the Amazon rainforest tends to suffer from drier
conditions.
And Australia endures extreme heat, drought and bushfires.
El Nino could offer a reprieve to the Horn of Africa, which recently
suffered five consecutive failed rainy seasons. El Nino brings more
rain to the Horn, unlike the triple-dip La Nina which desiccated the
region.
Historically, both El Nino and La Nina have occurred about every two
to seven years on average, with El Nino lasting 9 to 12 months. La
Nina, which takes hold when waters are cooler in the Eastern
Pacific, can last one to three years.
IS CLIMATE CHANGE AFFECTING EL NINO?
How climate change might be affecting El Nino is "a very big
research question," said DiLiberto. While climate change is doubling
down on the impacts from El Nino — layering heat on top of heat, or
excess rainfall on top of excess rainfall — it's less clear if
climate change is influencing the phenomenon itself.
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Scientists are not sure whether climate change will shift the
balance between El Ninos and La Nina, making one pattern more or
less frequent. If ocean temperatures are rising across the board, it
is unlikely the cycle would change, scientists said, as the basic
mechanics behind the phenomenon stay the same.
However, if some parts of the ocean are warming faster than others,
that could influence how El Nino plays out by amplifying temperature
differences.
(Reporting by Gloria Dickie in London. Editing by Angus MacSwan)
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