Hottest ever ocean temperatures recorded around the world

The surface temperature of the world’s oceans hit 21 degrees Celsius (70 degrees Fahrenheit) this week, a record-high, according to findings released Friday by European meteorological agency Copernicus.

We’ve collected reporting and insights about what the high ocean temperatures mean for climate change and the species inside.

• March, not August, is when oceans should be the warmest and seeing ocean temperature records now makes Samantha Burgess from the Copernicus Climate Change Service “nervous about how much warmer the ocean may get between now and next March.” She added that the marine heatwaves “are happening in unusual locations where we haven’t expected them.” This year is an El Niño year, so the oceans will be hotter than usual — but the weather phenomenon has not yet reached its peak, meaning temperatures will rise further. — BBC News
• Coral off the Florida coast are bleaching from the intense heat. There, temperatures reached 101.1 F, about as warm as the average hot tub. Some of the coral along the state’s Alligator Reef have persisted for thousands of years, but with temperatures this hot, they’re unlikely to survive. Marine biologists are trying to mitigate the damage by hauling crates of rescued coral onto shore and sheltering them in the shade. — Los Angeles Times
• The ocean absorbs the vast majority of the extra heat the world sees from anthropogenic climate change. All of the increased heat the world has seen over the past six decades has culminated in the ocean, effectively delaying how much we notice the planet warming. As water heats, however, it expands. The record-hot temperatures will, in turn, result in rising sea levels. — The New York Times

The ocean’s surface temperature this week is far above the seasonal average and breaks a record previously set in 2016, the warmest year ever recorded. July 2023 is widely expected to be the hottest month in history.

A study in 2019 found that marine heatwaves are becoming more common as the earth warms.

The effects to ocean species are akin to a wildfire sweeping through a forest: Heatwaves wipe out species, and can drive behavioral changes in some animals. Predatory animals, like sharks, can become aggressive in warmer temperatures because they are confused.