Wildfires that began smouldering in Indonesia’s rainforests and peat soils at the start of the year had burned about 1000 square kilometres by June. Then in July, the blazes started to accelerate, doubling that area in just a month, and then doubling it again. Hundreds of thousands of people have faced respiratory illness, and carbon emissions are on track to equal Indonesia’s catastrophic 2015 fires.

The acceleration came as the strongest El Niño on record started developing in the tropical Pacific. A blob of warm water began moving from Indonesia toward Peru, shifting atmospheric circulation eastward. Warm air that typically rises above the warm blob, raining out its moisture over Indonesia’s rainforests, was instead rising above the central Pacific. And rather than descending over East Africa, the resulting warm, dry air descended over Indonesia, encouraging slash-and-burn agricultural fires to spread out of control.

The super El Niño is still gaining strength and will persist for months, unleashing a panoply of extreme weather across the world. A stronger El Niño will likely mean stronger impacts – especially when it comes on top of 1.4°C of global warming.

“There’s more moisture in the atmosphere, there’s more energy in the system,” says Tim Stockdale at the European Centre for Medium-Range Weather Forecasts.

What might the next year hold? Past events suggest what extreme weather is likely and where it will hit.

As of the start of October, not a single full hurricane has formed in the Atlantic Ocean this year, the first time that has happened in more than a century. The El Niño circulation changes tend to amplify high-level winds and weaken low-level winds over the Atlantic, creating wind shear that breaks up hurricanes. “Those systems are being torn apart as they form,” says Nick Dunstone at the UK Met Office.

The flip side is that over the Pacific, the weakened winds reduce shear and encourage the air heated by the blob of warm water there to spin up into typhoons. And because the centre of rising air has shifted eastward, when these storms head toward Asia, they cover more distance and suck up more heat energy and moisture before landfall.

Nearly two dozen typhoons hit east Asia in the autumn during the three previous super El Niños. In October 2015, “super typhoon” Koppu destroyed thousands of buildings and killed at least 47 people in the Philippines. This came about two weeks after typhoon Mujigae set off tornadoes and landslides in China, killing at least 20, and super typhoon Dujuan killed at least two in Taiwan.

This year, typhoons have already blasted the Philippines and Japan, and more are likely to strike as sea-surface temperatures continue to rise.

November-December: Flooding, drought and disease in Africa

Northern and eastern Ethiopia have suffered crop failures and South Sudan is on the brink of famine after one of the driest June-September rainy seasons on record, a decline linked to El Niño.

As the El Niño strengthens through the autumn and winter, it is expected to bring heavy rainfall and flash floods to southern Ethiopia, Kenya and Somalia. Flooding killed almost 3000 people in eastern Africa during the 1997 El Niño and 700 people during the 2023 one.

At the same time, rainfall is forecast to reach the lowest levels in 75 years in countries like Malawi, Zambia and Zimbabwe in late autumn and winter. That threatens an even worse maize harvest failure than during the 2015-16 super El Niño, when tens of millions of people went hungry and hundreds of thousands of livestock died.

Although the risks are clear, the US, UK and other high-income countries have slashed foreign aid budgets in recent years. While the United Nations is allocating $100 million to high-risk areas as a stopgap, it has only been able to provide about a third of the necessary funding for El Niño response plans in vulnerable Somalia, Sudan and South Sudan.

“Weather does not have to mean disaster,” says Ilan Kelman at University College London. “The reason disasters have happened is because we haven’t invested in avoiding disasters.”

January-February: Flooding and landslides in the Americas

Peru, where El Niño was identified and named, tends to bear some of the greatest impacts. During the super El Niño in early 1998, massive rainfall turned a desert in Peru into a giant lake, washed away roads and bridges in Ecuador and buried infrastructure like a goldmine in Bolivia, killing hundreds of people. Flooding and disease killed more than 9000 people in Peru in the 1982-83 super El Niño.

At least 52 people have already been killed in Peru this year by flooding and landslides linked to the “coastal El Niño”. This occurs when the normally cold waters off Peru warm up, a phenomenon that often precedes the wider tropical Pacific warming of a full El Niño.

Heavy rains often extend to North America. California, where sea levels are now being raised by a giant swell of warm El Niño water known as a Kelvin wave, suffered hundreds of damaging landslides and mudslides in February 1998.

Rising waters can overwhelm sewage systems, contaminating drinking water and spreading diseases like cholera and leptospirosis, a bacterial infection that can be transferred from animals to humans. At the same time, standing water and warmer temperatures can help mosquitoes multiply and increase the transmission of malaria and dengue.

The massive El Niño rainfall across the top of South America in 1998 led to deadly outbreaks of cholera in Peru and other countries that spring. Meanwhile, torrential rains of up to 100 times the average in eastern Africa sparked a deadly outbreak of malaria as well as Rift Valley fever, a virus originating in livestock that can also be transmitted by mosquitoes.

Epidemiologists are worried about these hotspots not just because they are likely to be doused, but also because healthcare and sanitation systems are often under-developed, according to Rachel Lowe at the Barcelona Supercomputing Centre.

“The biggest problems tend to occur where unusual weather coincides with socio-economic inequalities,” says Lowe.

The world’s fourth mass coral bleaching event, which impacted 84 per cent of coral reefs, officially ended in June. But the respite may be short-lived.

Bleaching happens when warming waters disrupt photosynthesis by symbiotic algae, and the coral host rejects the algae. If the heat continues too long, the coral will essentially starve to death.

Because El Niño hinders the upwelling of cold, deep water, all three previous super El Niños were accompanied by mass bleaching. The US’s National Oceanographic and Atmospheric Administration (NOAA) has said reefs across almost all of the planet’s tropical oceans are now at high risk again. Sea-surface temperatures will probably peak at the end of austral summer.

Tropical coral reefs are already on the verge of collapse, undermining their benefits to a billion people, including providing food sources and coastal protection from storms. El Niño will probably cause widespread bleaching events there as well as outside the tropics, according to Michael Meredith at the British Antarctic Survey, who recently co-authored an article calling for ocean interventions including sunshades stretched over coral reefs.

“If it’s a tipping point, they won’t recover to the level that they were at before,” he says.

While El Niño is expected to peak at the end of the year, it will take three to four months for all its heat to be transported around the globe. Because of this lag, and because it comes in addition to global warming, 2027 is expected to be the hottest year on record, reaching a maximum during the northern hemisphere summer.

Heatwaves can cause tens of thousands of excess deaths, while also reducing crop yields and driving up costs. Past El Niños have increased inflation in some countries.

The biggest impact will be in often-vulnerable tropical countries, according to Liz Stephens at the University of Reading in the UK. She noted that temperatures reached 4°C above average in a heatwave in South Sudan during the 2023-24 El Niño.

“These events can be quite a shock compared to what communities are able to cope with, and can… surpass what the human body is physically able to deal with,” she says.

NOAA projects that the Pacific will likely return to weak El Niño or neutral conditions in April, May or June. Forecasts don’t extend beyond that yet, but strong El Niños in the past have often been followed by strong La Niñas, when enhanced winds increase the upwelling of cold, deep water. That cools the globe, but it also in many cases causes the opposite extreme weather, an especially devastating effect known as “climate whiplash”.

Drought and wildfires can kill vegetation and create a crust over the soil, reducing the land’s ability to absorb water. That increases flood and disease risk when La Niña finally brings rain. And small farmers often don’t have the resources to withstand a poor, wet harvest after a poor, dry harvest.

Some research has suggested that global warming will lead to wider swings between strong El Niño and strong La Niña, increasing the risk of whiplash in places like California and Spain. Kelman says that means we need to invest in making our food, health, transport and energy systems more resilient.

“We are much more frequently in either an El Niño or a La Niña than we are in the neutral phase,” he says. “We can and should be ready for it.”