Matthew England and Alex Sen Gupta from UNSW Sydney and Alistair Hobday from CSIRO discuss how a new El Niño will bring unprecedented ocean temperature records and extreme weather.
A version of this article was originally published by The Conversation (CC BY-ND 4.0)
The world’s oceans are the hottest on record for June, pushing past records set during the 2023–24 El Niño years.
Currently, the average sea surface temperature is less than 21°C in the warm and temperate oceans of the world. Before industrialization in the 1870s, the average temperature was about 19.6°C.
That may not sound like much of a difference. But heating the world’s oceans in this way requires a really large amount of energy. Of all the extra heat trapped in greenhouse gases from burning coal, gas and oil, more than 90pc has gone into the world’s oceans.
As a result, the oceans are warming rapidly. By 2025, the added heat was equivalent to about 12 Hiroshima nuclear bombs exploding every second of every day.
To find a climate analog comparable to what is happening now in the ocean, we would have to go back about 120,000 years before the last Ice Age. Back then, a slight shift in the earth’s orbit led to gradual warming over thousands of years. People have been experiencing the same effect for a little over a century.
But the heat in the ocean doesn’t just stay there. Warmer oceans generate stronger storms, more humid air, heavier rainfall and more heat in the air over the oceans, which can make global heat waves more frequent and intense.
The El Niño that is forming in the tropical Pacific right now is likely to be large. As it develops, we can expect to see warmer temperatures and more extreme events such as heat waves in the western Indian, tropical Atlantic and eastern Pacific Oceans.
Where are the hottest places on earth and in the ocean?
Europe is bracing for record-breaking heat. The seas surrounding the region and the enclosed seas are also incredibly hot.
Parts of the Mediterranean are up to 6°C warmer than the long-term average.
Parts of the North Sea are up to 3°C warmer than average.
The formation of El Niño led to sea temperatures about 1.24°C above average over the central eastern Pacific region.
There is a lot of heat under the surface as well. Subsurface conditions in the eastern Pacific are more than 6°C above average.
A typical El Niño lasts about a year. The full effect on atmospheric temperature becomes more apparent towards the end of the cycle. That means that while we can expect 2026 to be hotter – perhaps a new record – next year is likely to be even hotter, as ocean heat is returned to the surface. We saw this during the El Niño events in 2023–24 and 2015–16.
Steady ocean warming coupled with longer-lasting and more intense ocean heat waves pose a major threat to marine ecosystems such as coral reefs, seagrass meadows and coastal reefs. Research on the 2023–24 El Niño and the 2024 warm year showed widespread impacts.
From sea to land
What happens at sea does not stay there.
In June 2023, a record ocean heat wave broke previous temperature records across the North Atlantic Ocean. Soon after, large areas of Europe were hit by intense heat waves, while torrential rains caused deadly floods in Spain and massive forest fires broke out around the Mediterranean.
Rising ocean temperatures have many consequences.
The warm ocean cannot cool the land during the summer. Warmer oceans also lead to more evaporation, increasing humidity and fueling more heavy rain and flash floods. This can have devastating consequences.
During El Niño events, there is a clear spatial pattern. Regions that we expect to be warmer or cooler during El Niño probably indicate where we are least likely to experience ocean heat waves and more intense tropical storms.
Typical cyclone-prone areas such as the western Indian Ocean could see strong storms that dump heavy rain when they make landfall. El Niño tends to bring heavy rain and flooding in western South America and dry conditions in parts of Australia and Southeast Asia.
Can we prepare ourselves?
We are gaining a better understanding of how major climate drivers like El Niño shape the climate and how to use ocean data from around the world to develop better seasonal forecasts that authorities can use to prepare.
Over the past two years, we have improved our ability to predict ocean heat waves over the next three to four months in Australia, the United States and other regions. Forecasts give marine authorities the opportunity to take early action by reducing allowable catches and initiating efforts to conserve endangered species.
This initial breakthrough in ocean forecasting may be short-lived. The current US administration last year cut funding for climate data collection networks and worked to dismantle the National Center for Atmospheric Research.
This year, the administration announced it would end funding for a critical maritime surveillance network before withdrawing.
Continuous collection of ocean data is essential for ocean and land forecasts. If they are weakened or abandoned, we may face the challenge of dealing with the blinding effects of climate change.
Ending climate change mitigation will not stop it from happening. The only way to keep climate change from getting worse is to get to net zero as soon as possible. Until then, we must use forecasts to prepare for the inevitable.
Written by Matthew England, Alex Sen Gupta and Alistair Hobday
Matthew England is Professor of Science and director of the ARC Center of Excellence for Our Future Oceans. Since 1995, England has taught ocean physics and meteorology at the University of New South Wales. His expertise includes the physics of oceans and their role in climate variability and climate change.
Alex Sen Gupta is a Professor at the University of New South Wales in Sydney, where his work focuses on the role of the ocean in the climate system, how the ocean influences regional climate and what global climate models tell us about the future of the ocean.
Alistair Hobday is a principal research scientist in the Environment Division at the Commonwealth Scientific and Industrial Research Organization (CSIRO). His research covers many topics, including spatial management and migration of large pelagic species and determining environmental influences on marine species. The focus is on investigating the impact of climate change on marine resources, and developing adaptation strategies to support sustainable use in the future.
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