By Mandy Freund

The world is preparing for what could be the strongest El Niño in history. The United Nations has issued a stark warning that the planet has entered the "danger zone" of extreme weather, based on data indicating that the current El Niño will break all previous records.

El Niño is a naturally occurring weather phenomenon that drives variations in temperature and winds across the Pacific Ocean and influences weather around the globe. It is the warm phase of the El Niño–Southern Oscillation (ENSO), a recurring climate pattern that alternates with its cool counterpart, La Niña, typically every two to seven years. During El Niño, trade winds weaken and warm water that normally pools in the western Pacific shifts east toward the Americas, setting off knock-on effects on rainfall, storms and temperatures far beyond the tropics. The world has experienced many strong El Niños in the past, but none has been as exceptionally strong or has developed as quickly as this one.

So what is behind this potentially record-breaking event, and how might it affect weather worldwide?

How scientists measure El Niño

Scientists track El Niño activity using temperature data from the tropical Pacific Ocean near the equator. Historically, this involved simply measuring how high or low temperatures were across the region. Today, however, scientists and weather organizations — including Australia's Bureau of Meteorology — use a relative index. Rather than measuring temperatures alone, this index accounts for background warming due to climate change, making it far easier to identify how intense an El Niño is in a warming climate.

The current El Niño stands out for two main reasons:

It arrived extraordinarily early. El Niño typically peaks between November and January, but this one is already unusually warm early in the season and has yet to peak during summer.

It is extraordinarily hot. Recent data show the relative index for August was 2.3°C above average — stronger than in other El Niño years.

In Australia, El Niño years tend to bring hotter and drier conditions, though every event differs in its impacts. El Niño's influence on global temperatures also tends to lag: because the ocean releases stored heat gradually, its full warming effect on global average temperatures is usually felt in the year after the event peaks. This El Niño, however, is set to drive record-breaking global temperatures in 2027.

How is it affecting the world's weather?

This historic El Niño is already altering weather patterns around the globe, with the most direct and severe impacts in countries bordering the Pacific Ocean. Indonesia, for instance, spent this month battling massive wildfires, and scientists identify the current El Niño as a major driver of the increasingly fierce blazes. Along South America's west coast, the influx of warm Pacific water has historically disrupted fisheries by suppressing the upwelling of cold, nutrient-rich water that sustains marine ecosystems — one of the phenomenon's best-documented regional effects.

El Niño is also reshaping how and where cyclones form. Satellite imagery shows four active tropical cyclones in the Pacific, from near Japan to as far away as Hawaii — an extremely unusual situation. El Niño typically boosts cyclone activity in the eastern and central Pacific by carrying warmer water into those regions, and normally only one or two such cyclones are seen at a time.

Australia is somewhat more removed from El Niño's direct effects, but its presence will be felt more strongly as spring approaches. The Bureau of Meteorology's seasonal forecast indicates the country has so far had a textbook response to El Niño: temperatures are climbing — reaching an unseasonable 37°C this week in parts of northern Australia — and conditions are becoming drier. Much of eastern and central Australia can expect an unusually dry spring and summer, potentially heightening bushfire risk.

A record-breaking El Niño will not necessarily trigger catastrophic bushfires in Australia, however. Of the last three strong events, the robust El Niño of 1982 coincided with drought-like conditions, while during 1997-98 and 2015-16 some parts of Australia received drenching rain even as other regions barely registered any moisture.

What may lie ahead

The intensifying El Niño is likely to exacerbate the consequences of climate change. As it strengthens, countries worldwide will be forced to grapple with increasingly extreme weather. Tragically, the most disadvantaged communities will be hit hardest, with nearly 50 million people in vulnerable regions likely to be pushed into acute hunger. Farmers across the globe face more unpredictable weather, from crop destroying floods in South America to severe drought in parts of Africa — disruptions that ripple through global food supply chains, as past strong El Niños have shown in commodity production across multiple regions.

To protect people and ecosystems, governments must invest in robust research. More modeling capability is urgently needed to identify which regions will be worst affected by the strengthening El Niño — particularly in Australia, where there remains limited understanding of how climate change layered on top of a strong El Niño will affect local conditions.

This record-shattering El Niño is already compounding the destructive effects of climate change. But it may also prove to be the catalyst the world needs to finally abandon fossil fuels and curb its warming emissions.

The Conversation via Reuters Connect

Mandy Freund is a lecturer in Climate Science Geography at the University of Melbourne. She receives funding from the ARC Centre of Excellence for the Weather of the 21st Century.