The world’s oceans have just experienced their hottest June ever observed and could break new records in 2026, under the combined effect of El Niño and global warming, the European Copernicus Marine Observatory announced on Wednesday July 1.
The average surface temperature of the oceans, which cover two-thirds of the planet, reached 20.98°C on average in June, beating the previous record of June 2024 (20.89°C). The first half of 2026 as a whole is the second warmest on record, just behind the first six months of 2024.
“Current conditions could indicate the start of a new phase, leading us, once again, into uncharted territory,” warned Carlo Buontempo, director of the Copernicus Climate Change Service, quoted in a press release. “With ocean temperatures at these levels and El Niño on the horizon, we should see more temperature records falling in the months to come,” he added.
Temperatures were particularly high in June in the central and eastern equatorial Pacific, the area which is bearing the brunt of the effect of El Niño, a natural climatic phenomenon which warms surface waters, leading to episodes of drought, floods and record temperatures around the world.
The tropical Pacific Ocean recorded its hottest first half in history (26.91°C), beating by a hair the previous record set in 2016.
“With the arrival of an El Niño year (…), we can expect 2026 to be among the warmest years on record,” said Simon van Gennip, oceanographer at Mercator Ocean International, during an online press conference. “It is still impossible to say exactly how much,” he added.
In 2024, the latest year marked by this phenomenon, the average ocean surface temperature reached a record level of 20.9°C on average, before falling slightly the following year, according to Copernicus statistics.
This natural climatic phenomenon, which returns every two to seven years, adds to an underlying trend of warming of the oceans, due to the accumulation of greenhouse gases in the atmosphere. The oceans play a role in regulating the climate by absorbing 90% of the excess heat generated by human activities, notably the combustion of oil, gas and coal.
Marine heatwave
Since the start of the year, four-fifths (82%) of the global ocean has experienced marine heatwaves. Nearly half of the ocean surface suffered from strong to extreme heatwaves. The tropical Pacific Ocean and the Mediterranean Sea were particularly affected.
A closed sea, very sensitive to changes in the atmosphere, the Mediterranean thus experienced heat waves over almost its entire surface (98%) in the first half of the year, and a record temperature in June 2026 at 24.34°C.
The north-west Mediterranean, in particular, is affected by a heat wave which reached a record peak of intensity for the area on Monday, with an average of 5.2°C difference from normal values, the Institute of Marine Sciences (CSIC), based in Barcelona, said on Tuesday, stressing that this record was largely due to the heatwave that Europe has just experienced.
Marine heatwaves put severe strain on the least mobile marine species, going so far as to cause massive mortality among corals, gorgonians, sea urchins, molluscs, etc.
“It is important to monitor these phenomena (marine heat waves, editor’s note), because they have significant repercussions on the weather,” pointed out Simon Van Gennip, adding that these high temperatures could “provide additional energy to the atmosphere” to create “favorable circumstances” for extreme rain phenomena, such as “Mediterranean episodes”.
Warming oceans expand water, which raises sea levels. It also aggravates extreme weather phenomena such as intense rains or cyclones.
