Global sea surface temperatures reached 21.0 degrees Celsius (69.8 degrees Fahrenheit) in June 2026, according to a report from the Copernicus Marine Service. This temperature exceeded previous records for June set in 2023 and 2024.

The Copernicus Marine Service, an agency of the European Union, reported that the first half of 2026 was marked by persistently high sea-surface temperatures and widespread marine heatwaves across the global ocean. "Record global sea surface temperatures of 21.0 degrees Celsius (69.8 degrees Fahrenheit) in June beat the previous records in the same month in 2023 and 2024," the service stated. "Marine heatwaves expanded steadily throughout the period, ultimately affecting around 82 percent of the global ocean," said Simon van Gennip, lead oceanographer for the service.

"The Mediterranean, the central North Atlantic and the equatorial Pacific all emerged as hotspots, and these regional signals paint a consistent picture of an ocean under sustained thermal stress," van Gennip said. Carlo Buontempo, director of the Copernicus Climate Change Service, noted that "current conditions could indicate the beginning of a new phase, leading, once more, to uncharted territory."

Buontempo added that "with ocean temperatures at these levels and El Nino on the horizon, we are likely to see more temperature records fall in the coming months." El Niño is a weather pattern characterized by unusually warm waters in parts of the Pacific Ocean. This phenomenon introduces heat into the atmosphere and influences global wind, cloud, and weather patterns. Land and sea temperatures reached an all-time high in 2024 during the previous El Niño event.

A United Nations scientific assessment issued in June 2026 stated that the world's oceans were in a "deepening crisis" due to warming and rising seas. Oceans absorb about 90 percent of the excess heat resulting from human greenhouse gas emissions. Warmer oceans contribute to increased atmospheric moisture, which can intensify tropical cyclones and heavy rainfall. The thermal expansion of warming seawater also directly contributes to sea-level rise. Prolonged marine heatwaves can cause coral bleaching and death in tropical reefs.

Why It Matters

The record-breaking global sea surface temperatures reported by the Copernicus Marine Service in June 2026, surpassing previous highs from 2023 and 2024, indicate a continuation of ocean warming trends. This development aligns with a June 2026 UN scientific assessment that characterized the world's oceans as being in a "deepening crisis" due to warming and rising sea levels. The presence of El Niño, a natural weather pattern associated with warmer Pacific waters, is anticipated to contribute to further temperature increases, consistent with observed land and sea temperature highs during the 2024 El Niño event.

Ocean warming has direct implications for various environmental systems. As oceans absorb approximately 90 percent of excess heat from human greenhouse gas emissions, observed warmth in regions such as the Mediterranean, central North Atlantic, and equatorial Pacific points to broad thermal stress. Warmer oceans are linked to increased atmospheric moisture, which can fuel more intense tropical cyclones and heavy rainfall, while the thermal expansion of seawater contributes to sea-level rise, and prolonged marine heatwaves can lead to coral bleaching and the destruction of tropical reefs.