During the 2015-2016 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."
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 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.
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.
REUTERS
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