For 100 consecutive days between June 2 and Sept. 10, the global ocean outside of polar regions sustained record-high average sea surface temperatures, according to data from the Climate Reanalyzer, a platform overseen by the University of Maine’s Climate Change Institute in the US
On each of the 100 days, sea surface temperatures exceeded those on the same date in every other year on record since 1982. One of the highest readings occurred on Aug. 22, when global ocean sea surface temperatures reached 21.10° Celsius (69.98° Fahrenheit), according to the European Union’s Copernicus Climate Change Service.
The Climate Reanalyzer reported temperatures climbing even higher between Aug. 22 and 27, with average ocean sea surface temperatures hitting 21.18° C (70.12° F). The platform draws on global sea surface temperature data recorded by the US National Oceanic and Atmospheric Administration (NOAA).
These record temperatures are likely to remain elevated in the near future “given the state of the intensifying El Niño,” said Zachary Labe, a climate scientist at the US-based nonprofit Climate Central, which communicates climate change science.
In a Sept. 10 press briefing that discussed the Climate Reanalyzer data, Labe said this record ocean heat is part of a long-term trend driven by the human-induced climate crisis. Without a reduction in greenhouse gases, he said the oceans will continue to warm.
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It really shows that high sea temperatures are not confined to the sea; they affect marine life, the food and tourism industry, as well as humans’ day-to-day life.
Claire Bergin, researcher, ICARUS Climate Research Centre
“The driver of this record warmth is climate change,” he said, “and more than 90 per cent of that excess heat from burning fossil fuels and those greenhouse gas emissions goes into the ocean.”
Experts say the unprecedented ocean heat is affecting marine ecosystems, global weather patterns, and economies that depend on the ocean for food security, livelihoods and coastal protection.
Ocean heat affects ecosystems, economies and health
The ocean absorbs an exceedingly high amount of heat each year. An analysis published in Advances in Atmospheric Science found that during 2025, the ocean absorbed 23 zettajoules, a quantity of energy equivalent to about 12 atomic bombs exploding in the ocean every second of every day. This was more than a 43 per cent increase from the 16 zettajoules of heat the ocean took in during 2024.
Warming isn’t only affecting the sea surface layer, which extends to a depth of 200 meters (660 feet), but is reaching the deeper layers of the ocean, Labe said.
“All of this has significant impacts,” he said. “It impacts marine ecosystems. It shifts the geographies of all parts of the marine ecosystem food chain. It also impacts our economy — things like fisheries, tourism. It also impacts the physical climate system and weather. It can affect hurricanes, or it can affect marine ecosystems through coral.”
High sea temperatures are also known to drive land-based heatwaves, particularly in coastal areas, according to Claire Bergin, a researcher at the ICARUS Climate Research Centre at Ireland’s Maynooth University. Bergin collaborates with World Weather Attribution, a team of scientists who evaluate whether extreme weather events are attributable to climate change.
“There’s a direct link between increased sea temperatures and the intensity of land-based heat waves,” Bergin said in the press briefing. She said the heat waves Europe experienced over the summer, especially in coastal areas, were “exacerbated” by high sea surface temperatures.
Bergin said high sea temperatures were also linked to an increased wet bulb temperature on land — that is, the lowest temperature air that can be reached through evaporation, which has implications for humans’ ability to cool themselves. The higher the humidity, the more slowly moisture evaporates.
“Higher wet bulb temperatures negatively affect human health, as the high moisture content reduces our ability to regulate body temperature,” Bergin said. “It really shows that high sea temperatures are not confined to the sea; they affect marine life, the food and tourism industry, as well as humans’ day-to-day life.”
El Niño amplifies threats
While experts agree that climate change is primarily responsible for these high ocean sea surface temperatures, the current El Niño that began in June, which NOAA predicts to be “very strong,” could add fuel to the fire by amplifying the warming caused by human activity.
El Niño is a naturally occurring phenomenon that forms part of the El Niño–Southern Oscillation (ENSO) cycle, a process in which sea surface temperatures and atmospheric pressure fluctuate across the tropical Pacific Ocean.
The El Niño is the “warm” part of the cycle, occurring when Pacific trade winds weaken and warm water accumulates along the west coast of South America, which raises global temperatures.
Scientists expect the current El Niño will peak toward the end of 2026 and its force will continue into 2027.
However, the underlying trend of warming sea temperatures in response to climate change remains the primary concern for experts.
In the press briefing, Pickerell, the global director of the ocean program at the US-based nonprofit World Resources Institute, emphasised the importance of reducing greenhouse gas emissions to keep that trend in check. This, he said, is not the responsibility of the individual, but of industry’s “big emitters” to transition away from oil and gas. Pickerell is also head of the secretariat at the High-Level Panel for a Sustainable Ocean Economy, a group of global leaders committed to the protection and sustainable management of the ocean.
The Paris Agreement, signed in 2015, intended to limit global warming to 1.5° C above preindustrial levels, a threshold scientists identified as being critical for avoiding the most dangerous impacts of climate change. But according to a new report from the UN Environment Programme, global temperatures are now likely to surpass that threshold within the next few years, pushing the planet into increasingly dangerous territory.
“Ultimately, we need to cut emissions,” Pickerell said. “That is the key thing here.”
This story was published with permission from Mongabay.com.
