El Nino: What is it and how does it affect weather patterns?

It's back

With news that El Nino conditions have developed in the tropical Pacific for the first time in seven years, the stage has been set for a surge in global temperatures and disruptive weather and climate patterns. With record temperatures, devastating droughts and epic storms on the way, we look at what this weather phenomenon actually is and how it will impact you.

What is El Nino?

El Nino is a climate pattern that sees the unusual warming of surface waters in the eastern tropical Pacific Ocean. It is declared when the waters off the Pacific coast between Southern Mexico and Northern Peru rise 0.5°C (33°F) above the long-term average. Even in its mildest form it causes the Pacific jet stream to move south of its neutral position, triggering wide-ranging changes in weather and climate patterns around the globe, including devastating floods in South America and chronic droughts in Australia and Indonesia.

And La Nina?

La Nina is the opposite side of the fluctuation – a climate pattern that sees cooler than average sea surface temperature in the eastern tropical Pacific Ocean. It is caused by unusually strong, eastward-moving trade winds combining ocean currents to bring cold water to the surface in what's known as "upwelling". It brings heavy rains to Australia and India and drier conditions to the Americas. The 2010 La Nina brought the worst flooding in history to Queensland, Australia. And the great Dust Bowl drought of the 1930s is thought to have been caused by a decade of La Nina-like conditions.

Both are part of a larger weather phenomenon

The El Nino-Southern Oscillation (ENSO) is one of the most important climate phenomena on Earth, determined by the intricate interaction between the ocean and the atmosphere. It has the ability to change the global atmospheric circulation (the movement of air around the planet), which in turn influences temperature and precipitation across the globe. El Nino and La Nina are the ocean part of the equation, representing a “warm phase” and a “cool phase” respectively. The Southern Oscillation is the change in atmospheric pressure between the east and west tropical Pacific that accompanies these phases.

 

It’s all about push and pull

Climate scientist Michelle L’Heureux from the National Oceanic and Atmospheric Administration (NOAA) suggests thinking of La Nina and El Nino as events that push the weather system from the Pacific either east or west resulting in ripple effects worldwide. During an El Nino event, westward-blowing trade winds weaken allowing warm surface water to flow eastward towards the coast of northern South America. During a La Nina event those same trade winds strengthen, pushing the warm water back towards Australia and the rest of the western Pacific.

It was first observed by Peruvian fishermen in the 1600s

El Nino was first recognised by fishermen off the coast of Peru in the 1600s. When the warmer waters arrived, they noticed that it had a detrimental effect on their fishing stocks. The fishermen were also the ones who gave El Nino its name. The effects of El Nino often peaked during December so they christened it "El Nino de Navidad", the little boy of Christmas, in honour of the birth of Christ. La Nina, on the other hand, simply means the opposite: “Little Girl.”

 

El Nino has always packed a punch

The impact of El Nino has always been far-reaching. El Nino-related droughts and floods are believed to have led to the demise of the Moche civilisation in Peru. Its impact on crop yields between 1789 and 1793 in Europe is said to have triggered the French Revolution. And the severe drought caused by the 1876 El Nino is estimated to have killed 18 million people across India and China. Scientists have also noted its 'signature' in the tree rings of 500-year-old Douglas fir trees in New Mexico; thin for El Nino, thick for La Nina.

How often does El Nino occur?

El Nino doesn’t follow a schedule but generally occurs on average every two to seven years. Episodes typically last nine to 12 months but can go on for years. Australia’s CSIRO science agency, however, has noted that global warming has made El Nino and La Nina more frequent and unpredictable. Dr Mike McPhaden, a senior research scientist at the US government’s National Oceanic and Atmospheric Administration (NOAA), says this will translate into more frequent extreme droughts, floods, heatwaves, wildfires and severe storms.

No two El Nino are exactly alike

In recent years climate experts have noticed that El Nino (and La Nina) events come in all manner of varieties. The standard El Nino, such as it is, warms the eastern tropical Pacific Ocean and is known as a Conventional or Eastern Pacific El Nino. A Central Pacific El Nino, however, warms the mid-Pacific to a greater degree than the east or west. Throw in temperature fluctuations and you’ve got an entire spectrum of El Ninos. The variations change where the effects of that particular El Nino will be felt most and its intensity. Weak temperature increases of about 7-9°C (4-5°F) will have only moderate local effects on weather and climate. Strong increases of about 25-32°C ( 14-18°F) cause worldwide climatic changes.

Climate change has made the impact of El Niño worse

Australia’s government scientific organisation, CSIRO, have found that since 1960, human-caused greenhouse gas emissions have led to an increase in the “variability” of the El Nino-Southern Oscillation. This departure from the average often results in stronger El Nino and La Nina events. According to WMO’s State of the Global Climate Report the “double whammy” of a very powerful El Nino event and human-induced climate change will result in a 66% chance that the annual average near-surface global temperature will be more than 1.5°C (35°F) above pre-industrial levels between 2023 and 2027. 

The latest El Nino has already arrived

On 4 July 2023 the World Meteorological Organization declared that El Nino conditions had developed in the tropical Pacific for the first time in seven years and that the stage had been set for “a likely surge in global temperatures and disruptive weather and climate patterns”. The WMO urged governments around the world to prepare for the impact on health, ecosystems and economies. “Anticipatory actions [ahead of] this major climate phenomenon are vital,” warned WMO Secretary-General Professor Petteri Taalas.

And it’s set to be a record-breaker

Historically, El Nino typically peaks around December. But the 2023 El Nino is an early starter and that’s not good news. The longer time frame gives El Nino longer to ‘grow’, resulting in a one-in-four chance of it becoming supersized and causing life-threatening, extreme weather events. The WMO has said it expects the 2023 El Nino to be at least of moderate strength, but a recent spike in the IRI plume has led the US National Oceanic and Atmospheric Administration to predict that the 2023 El Nino will be stronger and continue through to March 2024.

El Nino has always triggered civil unrest

In 2011 Columbia University economist Solomon Hsiang made a startling discovery. He reviewed 234 civil wars that have broken out in some 175 countries since 1950 and found that one in five civil conflicts have been influenced by El Nino. Tropical countries like El Salvador (pictured) were twice as likely to experience unrest. It is believed that droughts caused by El Nino are largely to blame because they tend to exacerbate longstanding food shortages. “This represents the first major evidence that global climate is a major factor in organised patterns of violence,” Hsiang said.

El Nino helps to spread mosquito-borne diseases too

The World Health Organization has also noticed that in South America the risk of a malaria epidemic increases around five-fold in the year after an El Nino event. The number of malaria-infected Venezuelans and Columbians goes up by 33% and there is a post-El Nino boom in other mosquito-transmitted ailments like Rift Valley fever, dengue and Zika too. On 21 June 2023, WHO’s director general, Tedros Adhanom Ghebreyesus, warned governments they should prepare for an increase in the spread of these viral diseases.

How will El Nino affect the US?

During El Nino, trade winds weaken and warm water is pushed back east towards the west coast of the Americas. The Pacific jet stream moves south and spreads further east, leading to wetter conditions in the Southern states and warmer, drier conditions in the North. That’s not good news for the South, where climate change has already made dangerously heavy rainstorms more common. El Nino will make these storms heavier and more intense, resulting in life-threatening floods when inadequate stormwater infrastructure is overwhelmed.

 

The north may not escape the brunt

A strong El Nino event disrupts the global atmospheric circulation that helps distribute thermal energy (heat) across the surface of Earth. If it moves eastward, the northern regions of the US experience longer, colder winters often resulting in blizzards like the one that hit New York during the 1982-83 El Nino event. If it moves in the other direction, the opposite happens – like during the 1997-98 event when the Midwest experienced record-breaking warm temperatures in what became known as “the year without a winter.”

El Nino impacts the US in unexpected ways

Scientists studying the 1982-1983 El Nino discovered a host of unexpected repercussions the event had on the USA. A warm wet spring brought mosquitoes and encephalitis outbreaks to the East Coast. Hot, dry weather in Montana saw rattlesnake bites increase. And a cool, wet spring in New Mexico proved ideal for flea-ridden rodents and a rise in cases of the bubonic plague. Warm seas saw an increase in shark attacks off the Oregon coast and a large number of spine injuries in California were attributed to the weather-altered coastal sea floors.

There may be one silver lining for the US

Southerly winds from the Gulf of Mexico tend to weaken during an El Nino event, effectively putting a lid on the conditions that form Midwestern tornadoes. This is good news as the last La Nina treated the American Plains states as a punching bag with a barrage of hurricanes and tornadoes like the December 2021 tornado outbreak in Kentucky, Tennessee, Missouri and Arkansas, which resulted in many deaths and billions of dollars' worth of damage. Climate disruption has kept Atlantic waters warm, however, so forecasters are still expecting a slightly above-average number of storms.

Having said that, Hawaii might be at high risk

Of all the US states, Hawaii is perhaps the most vulnerable to the effects of El Nino. The increased odds of a tropical cyclone that come with any El Nino year combined with climate-fuelled ocean warming means that those storms are getting bigger and more frequent. There is concern that the islands aren’t ready, with a lack of preparedness unnerving residents. There are also fears that the recent devastating fires on Maui will leave the topsoil more exposed, resulting in dangerous mudslides.

Things are looking grim for Canada too

For Canada, El Nino generally brings drier, warmer weather, with farmers enjoying a longer than normal season. But an abnormally hot spring, plus wildfires that raged from Alberta all the way to the Maritimes in the East, means that decent rains are needed now and El Nino will deny them. John Gyakum, from McGill University's Atmospheric and Oceanic Sciences department, points out that those warmer El Nino temperatures can also lead to inclement weather – like the devastating ice storm in Québec during the 1998 El Nino event.

 

A severe El Niño literally makes days longer

When David Salstein and Richard Rosten of Atmospheric and Environmental Research, Inc. in Cambridge, Massachusetts studied the effect of the 1982-1983 El Niño they made an astounding discovery. The changes in the jet stream and trade winds were so intense that the angular momentum of Earth shifted slightly. Even more incredibly, in late January, at El Niño's peak, that shift stretched the length of a day by 0.2 milliseconds.

El Nino is Australia’s climate nemesis

As one of the driest countries on the planet, Australia is particularly vulnerable to the effects of El Nino. Reduced rainfall and higher temperatures turn its forests into tinderboxes and the resulting droughts decimate its agriculture. The government scientific agency CSIRO has warned farmers to monitor pasture growth and make stock adjustments and urged local bush fire brigades to increase hazard reduction burns after the recent wetter conditions have increased available fuel for bushfires. The International Monetary Fund is predicting a drop in the country’s real GDP growth as a result.

El Nino brings food insecurity to southern Africa

El Nino historically brings record heat temperatures and droughts to southern Africa, often leading to food insecurity in the region. South Africa's Agricultural Business Chamber noted that when El Nino hit the region in 2015 the production of staple crops such as maize dropped by almost three million tonnes. Countries like South Africa had to import maize to make up the shortfall – something they may not be able to afford this time around with the war in Ukraine driving prices sky high.

El Nino means higher food prices

El Nino is already affecting future food prices across the world, according to the Energy and Climate Intelligence Unit (ECIU). With grain supplies already squeezed in Ukraine and the threat of an El Nino-induced drought heading for Asia, people are already panic buying rice in India. The Asia-Pacific region grows 90% of the world’s rice and, according to the head of the ECIU’s International Programme Gareth Redmond-King, the confirmation of El Nino’s return has seen prices rise. As the climate crisis combines with Putin’s reluctance to agree to a grain deal, there are concerns they will go even higher. 

El Nino will add to the UK’s inflation woes

The UK imports almost 50% of its food. And half of that comes from areas of the world most vulnerable to heat, drought, flooding and other climate impacts. Gareth Redmond-King from the ECIU believes that makes the UK's food prices particularly vulnerable to the impact of El Nino. “We can’t simply grow ourselves out of the problem,” he says. British families already struggling to make ends meet could be in for a difficult couple of years.

 

The 1982-1983 El Nino is considered the worst ever

The 1982-1983 El Nino is widely regarded as the most devastating recorded, causing weather-related disasters on almost every continent. Australia, much of Africa and Indonesia suffered droughts, dust storms and wildfires. Peru was hit with the heaviest rainfall it had ever seen (with 11 feet/3m of rain where 6 inches/15cm was normal). Canada’s salmon harvest collapsed. Alaska registered record temperatures and typhoons struck Hawaii and Tahiti. In all, nearly 2,000 lives were lost and more than £10 billion ($13 bn) damages caused.

El Nino can have a positive impact on some countries

A study by the International Monetary Fund has shown that certain economies actually benefit from El Nino. Following the 2010 event, Argentina’s GDP rose by 1.08%, Canada’s by 0.85% and Mexico’s by 1.57%. How did that happen? El Nino led to a decrease in east coast hurricanes which was great for the Mexican oil industry. A warm weather influx meant that Canada’s fisheries yielded a greater output. And more rain helped Argentinian soybean farmers produce a bumper crop. Lime, almond, and avocado farmers in California benefitted from the wetter weather too.

Indigenous communities are often the worst affected

The impact of El Nino is most keenly felt by Indigenous communities who rely on the land and rudimentary agriculture to survive. The United States Environmental Protection Agency (EPA) has noted that both droughts and flooding have a very detrimental effect on the supply and quality of traditional foods, subsistence foods and cultivated crops on both sides of the Pacific. Flooding has washed away entire communities in Bolivia, Ecuador and Peru, while in Mindanao in the Philippines, communities struggle to feed their families.

 

The impact on the world’s stock of fish is biblical

El Nino also has a strong effect on marine life off the Pacific Coast. During normal conditions, upwelling brings cold, nutrient-dense water from the depths to the surface. But during El Nino, this process weakens or stops completely. Without these nutrients, there are fewer phytoplankton. This affects species of fish that eat phytoplankton and, consequently, everything that eats those fish too. The warmer waters can also bring species such as yellowtail and albacore tuna into areas whose temperatures would usually be too low. 

Seabirds end up in weird places

Peruvian boobies can usually be found hunting anchovies off the coast of Peru, venturing south to Chile and north to Ecuador, but rarely any further. But when El Nino comes and the anchovies disappear, they head further north in search of food. During the 1982-83 El Nino they were seen as far north as Panama, with a colony of 3,500 boobies roosting on Pachecha Island alone.

The very strange case of Mr Al Niño

The 1997-98 El Nino brought record rains to California – in fact, they were so relentless that angered Californians began taking out their frustrations on a man living in Nipomo. People began phoning him to scream obscenities and, bizarrely, to stay away from Cayucos. Most simply asked “Why are you doing this?”. Such was his notoriety that David Letterman contacted him with an invitation to appear on The Late Show. The man’s name? Alfonso Niño. Listed in the phonebook as Al.

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