Ocean Surface Temperatures Hit Record High, Raising Fears of Extreme Summer Heat

Temperatures on the ocean surface have hit a record high, raising fears of another burst of extreme heat this summer.

On 21 June, temperatures outside the polar regions exceeded the extraordinary highs observed at the same time in 2023 and 2024, the Copernicus Climate Change Service said on Wednesday.

It warned the new peak would probably bring “consequences for weather patterns, global climate and marine ecosystems”, not least because it would coincide with the earliest phases of an El Niño event they forecast to be the strongest in decades.

When the previous ocean record for June was set in 2023, scientists described the trends as “worrying”, “terrifying” and “bonkers” because they were so far outside their expectations. That presaged an El Niño and a period of devastating global heatwaves, floods and storms.

That 2023 record has now been surpassed and much of the world is once again seeing an alarming rise in temperatures. Last month, the UK and many other countries in Europe sweltered amid new heat records while Antarctica experienced unprecedentedly balmy winter conditions.

Although the focus is usually on land temperatures, oceans give a fuller picture of how much the climate is being pushed out of balance by human-caused warming.

Surface temperatures are affected by solar radiation, water currents and the buildup of heat in the depths.

Oceans absorb more than 90% of the excess energy in the Earth system, which is primarily caused by burning fossil fuels, such as oil, coal and gas. That imbalance hit a record 23 zettajoules last year, more than double the average of the previous two decades.

As a result, the oceans are warming at an accelerating rate. In 2020, the amount of heat being added to the oceans was equivalent to about five Hiroshima bombs a second. Last year, it was closer to 11 Hiroshima explosions a second. The UN’s secretary general, António Guterres, has warned “Earth is being pushed beyond its limits”.

Scientists said it was too early to say whether the sea surface heating would prove temporary or even worsen because annual peaks are usually registered in July and August.

But Carlo Buontempo, Copernicus director at the European Centre for Medium-Range Weather Forecasts, warned it could indicate the beginning of a new phase, leading, once more, to uncharted territory: “With ocean temperatures at these levels and El Niño on the horizon, we are likely to see more temperature records fall in the coming months.”

Copernicus is part of the EU’s space programme.