LONDON: Countries around the world are bracing for extreme weather later this year as the world grapples with El Nino – a natural weather phenomenon that fuels tropical cyclones in the Pacific and increases the risk of rainfall and flooding in the US and elsewhere.
On Thursday, the US National Oceanic and Atmospheric Administration (NOAA) announced that El Nino is now underway. A cooler La Nina pattern has dominated the last three years.
Scientists say this year is very worrying. Last year, 2016, when a strong El Niño was in full swing, the world saw its hottest year ever. Meteorologists expect this El Nino, coupled with extreme warming from climate change, to hit the world with higher temperatures.
Experts are also worried about what is happening in the ocean. El Nino means the waters in the eastern Pacific are warmer than usual. But even before this El Niño began, in May, the average global sea surface temperature was 0.1C (0.2F) warmer than any other record. It can exaggerate extreme weather.
„We’re in unprecedented territory,” said Michelle L’Heureux, a meteorologist with NOAA’s Climate Prediction Center.
El Niño could lead to $3 trillion in global economic losses this year, according to a study published last month in the journal Science, as extreme weather causes shrinking GDP, agricultural production, productivity and the spread of disease.
Governments in vulnerable countries are taking note. Peru has earmarked $1.06 billion to deal with the impacts of El Niño and climate change, while the Philippines – which is at risk from typhoons – has created a special government committee to deal with the predicted fallout.
Here’s how El Nino will play out and some of the weather we can expect:
What causes El Niño?
El Niño is a natural climate pattern that results from unusually warm waters in the eastern Pacific.
It forms when the east-to-west trade winds in the equatorial Pacific slow down or reverse as air pressure changes, though scientists aren’t entirely sure what initiates the cycle.
As the trade winds affect surface water warmed by the sun, this warm western Pacific water weakens and flows back into the cooler central and eastern Pacific basins.
During the 2015-16 El Niño – the strongest such event on record – anchovy stocks along the Peruvian coast crashed amid this influx of warm water. Almost a third of the coral reefs on Australia’s Great Barrier Reef died. In very warm waters, corals excrete living algae, turning them chalky and white.
This buildup of warm water in the eastern Pacific transfers more heat to the atmosphere through convection, creating thunderstorms.
„When El Nino moves that warm water, it’s going to move where the thunderstorms are,” said NOAA meteorologist Tom DiLiberto. „That was the first atmospheric domino to fall.”
How does El Niño affect global weather?
This change in storm activity affects the current of fast-flowing air – known as the subtropical jet stream – pushing its path south and straightening it into a flat stream that provides similar weather at the same latitudes.
„If you’re changing where the storm highway goes … you’re changing what kind of weather we’re expecting,” DiLiberto said.
During El Niño, the southern part of the United States experiences cooler and wetter weather, while parts of the western United States and Canada are hotter and drier.
Hurricane activity weakens as storms fail to form in the Atlantic due to wind changes, sparing the United States. But tropical cyclones are getting a boost in the Pacific, with storms often spinning toward vulnerable islands.
Parts of Central and South America experience high rainfall, although the Amazon rainforest suffers from drier conditions.
Australia endures extreme heat, drought and wildfires.
El Nino could provide a reprieve for the Horn of Africa, which has recently failed five consecutive rainy seasons. El Niño brings more rain to the Horn, unlike the triple dip La Niña that dries the region.
Historically, both El Niño and La Niña have occurred on average every two to seven years, with El Niño lasting 9 to 12 months. La Niña, when the water in the eastern Pacific is cooler, lasts one to three years.
Does climate change affect El Niño?
How climate change might affect El Niño is a „huge research question,” DiLiberto said. While climate change doubles the impacts of El Niño — layering heat on top of heat or more precipitation on top of more precipitation — it’s unclear whether climate change is affecting the phenomenon itself.
Scientists aren’t sure if climate change will alter the balance between El Niños and La Nina. If ocean temperatures are increasing across the board, the circulation is unlikely to change, the scientists said, because the basic dynamics behind the phenomenon remain the same.
However, if some parts of the ocean warm faster than others, it can amplify temperature differences and affect how El Nino plays out.
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