Kategorie: News
What’s happening behind the scenes with the reefs amid “extreme weather”
While meteorologists in Hamburg were discussing public perceptions of heat waves at this year’s Extreme Weather Congress, ocean data from that same summer provided its own, independently measured confirmation: The oceans also experienced a record-breaking summer in 2026—with direct consequences for coral reefs worldwide.
According to the Copernicus Climate Change Service, June 2026 was the warmest June ever recorded for the world’s oceans, and in August, the global ocean surface temperature reached a new record high of 21.11 degrees Celsius. By the end of June, approximately 82 percent of the world’s ocean surface was already experiencing a marine heatwave. A heatwave is defined as temperatures higher than those typically observed on 90 percent of past measurement days at that location—for at least five consecutive days. European waters were not spared either: in some areas, the Mediterranean, North Sea, and Baltic Sea were up to 5 degrees above the long-term average.
Reefs on Red Alert
The consequences are particularly evident in Florida: In September 2026, the National Oceanic and Atmospheric Administration (NOAA) raised the coral reefs around the Florida Keys and the Dry Tortugas to Bleaching Alert Level 4, and large parts of Florida Bay to Level 5—the highest warning level ever issued, associated with coral bleaching and die-off that had already been observed. Incidentally, NOAA has had to expand its coral bleaching alert scale in recent years because the previous categories no longer adequately reflected the extreme values observed.
The long-term trend is just as clear: According to data from the Australian Institute of Marine Science, nearly 10 percent of the world’s hard coral cover has already disappeared over the past 40 years—primarily due to repeated global heatwaves in the oceans, not isolated extreme events. Researchers emphasize that corals can recover from individual bleaching events if temperatures subsequently drop again. However, if heat waves occur too frequently or are too intense, the reefs simply lack the time to regenerate.
A Potentially Historic El Niño
Additional stress is on the horizon for the coming months. Since June 2026, an El Niño has been developing in the tropical Pacific, and according to the U.S. National Oceanic and Atmospheric Administration (NOAA), it continues to intensify. According to current forecasts from several international climate models, there is about a 75 percent probability that a historically strong event will occur between October and December 2026. It would be even stronger than any El Niño phase documented since 1950. According to the Climate Prediction Center (CPC), the probability of a “very strong” El Niño during the winter of 2026–27 is over 90 percent.
This is serious news for coral reefs: The fourth global coral bleaching event (2023 to 2025) was already significantly fueled by the preceding El Niño and reached an unprecedented scale. NOAA forecasts predict that, by the end of 2026, nearly half of the world’s ocean surface could be affected by harmful heatwaves due to the new El Niño event—with a particularly high probability off the coasts of California and Mexico, as well as in the Indian and Southern Oceans. Reefs, already weakened by the unusually hot summer of 2026, would thus have little time to recover before the next wave of stress sets in.
Further information:
WorldAtlas – The Warmest The Oceans Have Ever Been
The Conversation – Marine heatwaves are cooking our ocean ecosystems
Inside Climate News – Coral Reefs Can Recover But Relentless Marine Heat Waves Won't Let Them
NOAA Coral Reef Watch – Announcements
The Invading Sea (Kristopher Karnauskas)
IRI Columbia University – ENSO Forecast
NOAA Climate Prediction Center – ENSO Diagnostic Discussion