Oceans hit hottest June on record

Global ocean surface temperatures reached their highest June levels on record, European scientists said Wednesday, raising concerns that more heat records could fall as El Niño develops and climate change continues to warm the planet.

Two services under the European Union’s Copernicus Earth observation program said they independently confirmed record sea surface temperatures in June. The Copernicus Climate Change Service said global ocean temperatures outside the polar regions reached 20.86 degrees Celsius, or 69.54 degrees Fahrenheit, on June 21, surpassing the 20.83 degrees Celsius, or 69.49 degrees Fahrenheit, observed in 2023 and 2024. The Copernicus Marine Service recorded 21.0 degrees Celsius, or 69.8 degrees Fahrenheit, beating previous June records from 2023 and 2024 by 0.1 degree Celsius.

“The first six months of 2026 were characterised by persistently elevated sea-surface temperatures and widespread marine heatwaves across much of the global ocean,” the Copernicus Marine Service said in a statement.

Simon van Gennip, lead oceanographer for the Copernicus Marine Service, said marine heatwaves “expanded steadily throughout the period, ultimately affecting around 82 percent of the global ocean.” He said the Mediterranean, the central North Atlantic and the equatorial Pacific “all emerged as hotspots,” adding that the regional patterns “paint a consistent picture of an ocean under sustained thermal stress.”

Carlo Buontempo, director of the Copernicus Climate Change Service, warned that current conditions may signal a shift. “With ocean temperatures at these levels and El Niño on the horizon, we are likely to see more temperature records fall in the coming months,” Buontempo said. He said the world could be heading into “uncharted territory” and that conditions “could indicate the beginning of a new phase.”

El Niño is a naturally occurring climate pattern in which the central and eastern tropical Pacific Ocean becomes warmer than usual for months at a time. Scientists said the onset of a potentially powerful El Niño could further boost ocean and atmospheric heat in 2026 and into next year. Al Jazeera reported that El Niño can influence wind, cloud and weather patterns worldwide and raise the risk of extremes, including floods in Peru, droughts in parts of Africa and wildfires in Australia.

Richard Allan, a professor of climate science at the University of Reading in the United Kingdom, said the records match long-established climate science. “It’s consistent with what we’ve known for a long time — that the planet is warming because we’re emitting vast quantities of greenhouse gasses, primarily from fossil fuel burning, into the atmosphere and that’s stifling the ability of the planet to lose its heat to space,” Allan told NBC News.

Oceans absorb about 90% of the excess heat linked to human-caused greenhouse gas emissions, including carbon dioxide from burning oil, coal and gas. Warmer oceans can increase moisture in the atmosphere, fueling tropical cyclones and destructive rainfall, and they contribute to sea-level rise because water expands as it warms. Prolonged marine heatwaves can also create dangerous conditions for tropical reefs, where corals may bleach and die.

The findings came as heat gripped parts of the United States and Europe. More than 46 million people in the U.S. were under extreme heat alerts Wednesday, according to the National Weather Service, which warned that “dangerous heat” would build across the central and eastern U.S., with highs in the mid-to-upper 90s and some places above 100 degrees. The Ohio Valley, Mid-Atlantic and Northeast were expected to see record-breaking temperatures through Thursday.

In Europe, records were broken last week. World Health Organization chief Tedros Adhanom Ghebreyesus said more than 1,300 excess deaths had been recorded since June 21 “linked to high temperatures in Europe.” France’s national health ministry said Sunday that the country had about 1,000 more deaths than expected during the previous week amid its record-breaking heat wave.