Global ocean sea surface temperatures reached the highest levels recorded for June, surpassing marks set during the 2023ā24 El NiƱo period. The average temperature across tropical and temperate oceans now stands just under 21Ā°C, compared with roughly 19.6Ā°C before widespread industrialization in 1870. Although the increase appears modest, it represents an enormous addition of energy, with more than 90 percent of extra heat from greenhouse gases absorbed by the oceans. In 2025 this added heat equaled the energy of about twelve Hiroshima-scale nuclear bombs detonating each second. Comparable conditions last occurred around 120,000 years ago, before the most recent ice age, when gradual orbital changes warmed the planet over millennia rather than within a single century. Waters surrounding Europe have been especially warm, with parts of the Mediterranean up to 6Ā°C above the long-term average and sections of the North Sea 3Ā°C warmer than normal. The emerging El NiƱo has already raised sea surface temperatures by about 1.24Ā°C across a broad area of the central eastern Pacific, while subsurface temperatures there exceed the average by more than 6Ā°C. Hotter oceans intensify cyclones, increase atmospheric moisture, and heighten rainfall, while also raising the likelihood and severity of heat waves on land. A typical El NiƱo persists for roughly one year, with its strongest influence on atmospheric temperatures appearing toward the end of the cycle. Consequently, 2026 is expected to be exceptionally warm and 2027 potentially hotter still as stored ocean heat returns to the surface. Persistent ocean warming and more frequent marine heat waves threaten coral reefs, seagrass beds, and coastal ecosystems. In June 2023 a major marine heat wave in the North Atlantic preceded intense European heat waves, extreme rainfall, and Mediterranean wildfires. Rising ocean temperatures reduce the seaās capacity to cool adjacent land, boost evaporation, and fuel sudden heavy rains and flooding. During El NiƱo years, warmer or cooler regions align with areas more or less prone to marine heat waves and stronger tropical cyclones, affecting rainfall patterns across the western Indian Ocean, South America, and Australia.
