World's oceans hit hottest temperature ever recorded in August as El Niño takes hold

The average global sea surface temperature outside polar regions reached 21.1°C on Saturday. The world's oceans have reached their highest daily temperature on record, with global sea surface temperatures hitting 21.1°C on 22 August - a new high made particularly striking by the time of year, according to the European Union's climate change data. The reading, recorded by the EU's Copernicus Climate Change Service, narrowly surpassed the previous daily record of 21.09°C, set in March 2024. Ocean temperatures typically reach their global peak in March and April, following the southern hemisphere summer, Copernicus explains. This new record being set in August, when temperatures would normally be declining, highlights the persistent warmth spreading across the world's oceans. The latest figure also beats the previous August record of 20.98°C, set in 2023. While swimmers may like warmer oceans, the consequences are devastating and wide reaching for both humans and animals. What is the link between El Niño and warmer oceans? The record comes as a strong El Niño develops in the tropical Pacific, adding further heat to an ocean that has already warmed significantly over decades because of human-driven climate change. El Niño is expected to strengthen in the coming months, with the World Meteorological Organization forecasting a strong event. Copernicus seasonal forecasts suggest it could reach levels not seen for several decades. But scientists caution against viewing El Niño as the sole explanation for the record. “This record is another clear signal of an ocean under growing stress,” says Samantha Burgess, strategic lead for climate at the European Centre for Medium-Range Weather Forecasts. “El Niño is adding heat to the system, but it is doing so on top of decades of human-driven warming,” she says. What is the problem with warmer oceans? "From the Atlantic waters off Ireland to the Mediterranean Sea, Europe's seas are experiencing an alarming surge in temperatures," Thomas Frolicher, an environmental physicist at the University of Bern, Switzerland, said in a study published last week. "Our research shows clearly that this is being driven by climate change, in particular by the continued burning of fossil fuels," he adds. The consequences of warmer oceans stretch from marine ecosystems to coastal communities. Higher sea temperatures increase the likelihood and intensity of marine heatwaves, which can damage coral reefs and seagrass meadows and disrupt marine food webs. Fisheries and aquaculture industries can also be affected as marine species move in response to changing conditions. The global ocean has already experienced a sharp increase in marine heatwaves, with the number of marine heatwave days more than tripling since the early 1990s, according to Copernicus. Warmer seas also contribute to rising sea levels because water expands as it heats. At the same time, a warmer ocean can transfer more heat and moisture into the atmosphere, potentially increasing the intensity of some rainfall and storm systems. Another concern is that the ocean absorbs a large share of the carbon dioxide produced by human activity, but warmer water is less efficient at taking up CO2, Copernicus data revealed, noting that continued warming could weaken one of the planet's important carbon sinks against climate change. Scientists are now watching to see whether the latest record proves to be a short-lived spike or becomes part of a more persistent period of extreme ocean warmth.