Adugna Woyessa was a little boy the first time drought tore his country apart. As harvests failed in rain-starved regions of Ethiopia in the early 1970s, and his school turned a classroom into a grain store for farmers to send aid, he had no idea that scientists were beginning to connect the force parching its fields with cyclical shifts in trade winds that had long supercharged violent weather from South America to Australia.

The now notorious El Niño – Spanish for “little boy” – was named by fishers in the Pacific in the 1800s, but it was not until the 1970s that scientists understood its global nature and began to piece together the historical impact of the natural weather pattern characterised by hot years and brutal extremes.

The 1972-73 El Niño warmed Peruvian waters to levels that collapsed the world’s largest anchovy fishery – prompting scientists to conduct the first forecast of its state the following year – and brought harsh drought to south Asia, the Sahel and parts of east Africa ahead of an oil crisis that deepened global hunger. In Ethiopia, protests against the emperor’s handling of the famine helped a military coup that ushered in a communist dictatorship.

“El Niño is one of the most challenging climate phenomena,” said Woyessa, who grew up to become an epidemiologist at the Ethiopian Public Health Institute and has studied its effects on malaria epidemics. “Nutrition is everything for your capacity to withstand the challenges of its negative impacts on human health.”

All too often, though, nutrition is what El Niño takes away from those who most need it. Woyessa was in high school when a stronger El Niño hit a decade later in 1982-83, forcing some of his classmates to travel 150km to help with harvests on state farms. By his first year of university, further crop failures and civil war had escalated widespread hunger into an even more ruinous famine, which drew global attention through the Live Aid concert. Woyessa and his fellow students took turns helping people in shelters near their college. “We had two breads in the morning, and we were supposed to share our breakfast.”

Scientists are quick to caution that climatic shifts are only one factor among many when a society collapses, but at the extreme end of the spectrum, El Niño can spell apocalyptic suffering. In the worst El Niño years in the 19th century, the death toll from famines in India, China and Brazil stretched into the tens of millions. There is some evidence to suggest it set the scene for the French Revolution in the 18th century with erratic weather that ruined harvests, and it helped the Spanish conquer the Inca empire in the 16th century with rains that nourished the desert vegetation that sustained their march. Looser theories suggest it brought down ancient civilisations from Egypt to China.

This year, El Niño is back – and scientists fear it will resemble a young man more than a little boy. The National Oceanic and Atmospheric Administration in the US said El Niño conditions had formed in the Pacific last week and carried a 63% chance of being “very strong” by the peak near the end of the year. Australia’s Bureau of Meteorology followed on Tuesday, warning it would worsen the extreme heat and wildfires that engulf the country each year.

Some scientists have informally dubbed it a “super” or “Godzilla” El Niño based on the expected size of the temperature anomaly, which will push global heat higher at a time when extreme weather events such as Europe’s recent heatwaves and slew of storms are pushing the boundaries of what societies can handle. The World Meteorological Organization (WMO) used more measured language when it warned us to prepare for its return earlier this month, arguing a wide spread in model results made it too early to call its strength.

But even if it falls short of doom-laden predictions, it will be arriving amid unprecedented conditions that will make its effects more complex. Scientists say next year is almost certain to be the hottest on record, while a host of economic factors have left vulnerable countries more exposed. “My worry is not for the El Niño alone,” said Sonali McDermid, a climate scientist at New York University who shares the WMO’s caution about its intensity. “I’m worried about the confluence of multiple stressors happening at the same time.”

About half of the world’s 68 poorest countries are experiencing debt distress or at high risk of it, the International Monetary Fund warned in March, and the Iran war has since led to high energy prices and restricted fertiliser supplies that have weakened buffers against weather shocks. This month, the Famine Early Warning Systems Network projected 115-125 million people would need urgent food assistance by December, with risks of famine in Sudan, South Sudan and Somalia. The gutting of US overseas aid and the shrinking of European development budgets means less support may come when crises hit.

On Thursday, the threat posed by El Niño prompted the UN’s World Food Programme and its Food and Agriculture Organization to issue their first joint appeal for funds to avert a crisis before it happens. Citing research that shows every $1 spent in “anticipatory action” saves $7 in humanitarian relief costs, the agencies said they were $167m short of the $202m needed to help 8.8 million people with drought-resistant seeds, flood defences, water storage systems and cash transfers.

The good news, if there is some, is that El Niño is not expected to lead to worse outcomes for crops at a global scale, as gains in some regions typically offset losses in others, but the losers will include those least able to cope. Many of the African and Asian countries most exposed have also been hit hard by fertiliser shocks, and have some of the highest levels of food import dependence and debt stress, said Anne Jellema, the executive director of 350.org, a climate campaign group. “That means El Niño removes the last domestic lifeline for people who can’t access markets, increasingly can’t get humanitarian aid, and can’t move around freely.”

Shockwaves are also set to be felt in the rich world as El Niño brings stronger heatwaves and wider spread of some vector-borne diseases. Its arrival “persistently” slows improvements in mortality even in wealthy countries such as the US, Australia, Japan and South Korea, according to a study published in January in Nature Climate Change.

To some degree, the damage done by El Niño has in recent decades been checked by a level of predictability – but it provides a taste of the cascading horrors that climate scientists warn will destabilise societies as the planet heats up.

Deepened by geopolitical tensions, high energy and fertiliser prices and fragile supply chains, El Niño-related shocks may be “increasing the likelihood of compound and non-linear systemic impacts”, a study by the European Commission’s Joint Research Centre warned on Monday, with knock-on effects that run the gamut of economic sectors connected to the natural world.

“A plausible transmission pathway would run from droughts, floods and heat stress affecting agricultural production, labour productivity, water availability, hydropower generation and transport systems, to higher food and energy prices, inflationary pressure, fiscal stress and weaker borrower repayment capacity,” the authors wrote.

Can such calamities be avoided next year? El Niño does not have to be “a recipe for disaster”, according to the WMO, which said its forecasts are more a call to action before hazards escalate into crises. Its secretary general, Celeste Saulo, urged the world to intensify efforts to build multi-hazard early warning systems, as only 128 countries report that they have such systems in place.

Climate campaigners, meanwhile, have called for the cancellation of global south debt and the funding of social protections through windfall taxes on excess profits of oil and gas companies, rather than funding fossil fuels. “There’s a lot of research showing that targeted social protection is way more effective than subsidising fossil fuels and fertilisers because it goes to the people who need it most,” said Jellema.

António Guterres, who ends his terms as UN secretary general at the end of this year, has been making similarly desperate calls to global leaders for years – pleading with them to break the addiction to fossil fuels that has driven the overheating of the planet and the degradation of the natural world. The world has warmed by about 1.3C since the Industrial Revolution, and temperatures are rising so fast that the worst El Niño years of the recent past – such as 1997-98 – are far less hot than current years in which the system shifts to La Niña, its cooler counterpart.

For Woyessa, the rise in temperatures and loss of forests had disrupted rainfall patterns even around the village he grew up in. The river he used to swim in as a boy has been reduced to a small stream and the rainfall that previous generations used to rely on for planting crops has grown erratic. When he used to phone his late father, he added, asking about rain was a typical way to start a conversation.

“The main concern is the shifting of the rainy season,” he said. “The onset is totally changed compared with my childhood.”