Is El Niño changing the weather?

Ian Evenden January 28, 2016

Floodwaters have been rising along the lower Mississippi river in the United States, causing an estimated $1billion of damage, both physical and economic. Meanwhile, in Ethiopia, the worst drought in decades has left more than eight million people in need of emergency food aid. In Bolivia, Lake Poopó, the country’s second-largest body of fresh water, stands at 2% of its average level. Near Hawaii, a tropical storm formed in January for only the third time in 40 years. Oh, and NASA says 2015 was the warmest year on record.

Such disparate events, many of them thousands of miles apart, can be completely natural and, coming after the hottest year since records began, we can’t rule out man-made interference. But there may be a common cause behind their ferocity: El Niño.

This curiously named phenomenon (meaning “little boy” or “the Christ child” in Spanish) is a periodic warming of the tropical Pacific Ocean, specifically the waters off the coast of Peru, reaching across to the International Date Line. It was first recognised by Spanish fishermen in the 1600s and got its name from the time of year the warmer water makes itself felt through a drop in fish numbers – the end of December.

In order to qualify as an El Niño event, the sea surface temperature must rise 0.5ºC above average for a period of three months. This warming period occurs semi-regularly every two to seven years, then lasts nine to 24 months, and is able to affect the atmosphere – and, therefore, the weather – of our whole planet.

And it’s happening right now.

A “noisy system”

Winds across the Pacific generally blow from the east, pushing the surface waters to the west and causing cold, nutrient-rich water to well up close to the coast of South America. Thanks to this, surface temperatures are cool, the fish population booms and wet stormy weather, which tends to form over warmer waters, is pushed to the west and affects Indonesia and other parts of Asia. In an El Niño year, however, these winds weaken and the system reverses.

“1997-8 held the record for the number of strong tropical cyclones in the north Pacific (17), until 2015 smashed it with 21.”

“The climate in the tropical Pacific is a noisy system that’s bouncing back and forth between several states,” says climate scientist Dr Chris Brierley of University College London. “As it levels off, it can get a kick in the right direction, what’s referred to as a westerly wind burst. This week or so of wind counteracts the normal current for a little bit and acts as a trigger that pushes you into an El Niño.

“The tropical Pacific is a big convection cell,” says Brierley. “Imagine the warm waters over by Indonesia are a radiator that’s created lots of hot air, which is rising, and then because of the structure of the wind and the spin of the Earth it hits the top of the atmosphere as it rises, and some of it heads off to South America where it sinks and cools and you get a sort of return flow. So you’ve got one big convection flow driven by warm waters over by Indonesia. When you have an El Niño, you start having predominantly warm waters over in the east Pacific as well. So you’re moving the position of your heat source in these big global circulations.”

The El Niño that began in 2014 and has persisted into 2016 isn’t typical, with sea temperatures 3ºC higher than usual – leading Brierley to refer to it as “a whopper”. The current event bears similarities to the powerful El Niño of 1997-8, which saw record rainfall in California, drought in Indonesia and is estimated to have caused the death of 16% of the world’s coral reefs thanks to increased water temperatures. 1997-8 held the record for the number of strong tropical cyclones in the north Pacific (17), until 2015 smashed it with 21.

The phenomenon dates back a lot further than that, though. “The oldest is probably 100-something million years ago, they’ve been around a very long time and are an inherent part of having an ocean,” says Brierley. “But whether they’ve got the same properties all the way through is a different matter.”

Stacking on top of man-made climate change

As the warmest year on record, we could expect 2015 to come up with some violent weather on its own, without help from the Pacific. “2015 was remarkable even in the context of the ongoing El Niño,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said in a statement. “Last year’s temperatures had an assist from El Niño, but it is the cumulative effect of the long-term trend that has resulted in the record warming that we are seeing.”

“The human contribution to the atmosphere can have an influence on El Niño itself.”

The high temperatures are also being caused by man-made climate change and the El Niño effect simply stacks on top, as Brierley explains: “Presently it’s the biggest [El Niño] that’s ever been recorded. But there’s a subtlety in that because El Niños are a variability about the average climate state, and clearly we’re changing the climate state of the world. Currently, we’re warming the whole world up.”

The human contribution to the atmosphere can have an influence on El Niño itself. “Another thing that’s happening at the moment is that there’s massive amounts of tropical forest burning in Indonesia, for palm oil plantations and the like,” says Brierley. “The human-set fires are raging out of control due to the fact that, by changing where the rain is happening, there’s a drought going on in Asia, so there’s rather a worrying amount of burning going on over there.”

“El Niño may be able to affect weather worldwide, but Brierley doesn’t think it’s to blame for Britain’s unseasonable warm winter.”

El Niño may be able to affect weather worldwide, but Brierley doesn’t think it’s to blame for Britain’s unseasonable warm winter – or the second largest snowstorm in New York since 1869. In an El Niño year, the weather across the UK tends to be warmer and wetter at the beginning of winter but becomes drier and colder as the season marches toward spring. We’ve clearly seen the first part of that, but as 2016 advances a cold, dry period has yet to appear.

And while El Niño can have an effect in the Atlantic, and the smaller ocean has its own warming oscillation that’s weaker than the much larger Pacific’s, they’re both overwhelmed by local weather conditions before they can really make themselves felt in Europe.

So the answer to the question that opened this article is: “It depends on where you live”. While it would be easy to point to the periodic warming of the Pacific as a scapegoat for climate woes, we should perhaps look to ourselves for the root cause of the bad weather El Niño merely amplifies.

Images: Department for International Development, NASA and US Geological Survey used under Creative Commons