Global oceans were warmer last month than any other May in records stretching back to the 19th century, the European Union’s climate monitoring unit reported Wednesday.

Sea temperatures at a depth of about 10 meters were a quarter of a degree Celsius higher than ice-free oceans in May averaged across 1991 to 2020, according to the Copernicus Climate Change Service (C3S).

Year-round, long-term trends have added 0.6C to the ocean’s surface waters in 40 years, said C3S deputy director Samantha Burgess, noting that April had also seen a new record for heat.