Ocean surface temperatures have reached a record high for June, raising concerns about another summer of extreme heat, according to the Copernicus Climate Change Service. On 21 June, temperatures outside the polar regions exceeded the extraordinary highs observed at the same time in 2023 and 2024.
Record-breaking ocean heat
Copernicus warned on Wednesday that the new peak would likely bring “consequences for weather patterns, global climate and marine ecosystems,” particularly as it coincides with the early phases of an El Niño event 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 expectations. That presaged an El Niño and a period of devastating global heatwaves, floods, and storms.
Broader climate implications
Last month, the UK and many other European countries sweltered under new heat records, while Antarctica experienced unprecedentedly warm winter conditions. Although the focus is often on land temperatures, oceans provide 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, primarily caused by burning fossil fuels such as oil, coal, and gas. That energy imbalance hit a record 23 zettajoules last year, more than double the average of the previous two decades.
Accelerating ocean warming
As a result, the oceans are warming at an accelerating rate. In 2020, the amount of heat added to the oceans was equivalent to about five Hiroshima bombs per second. Last year, it was closer to 11 Hiroshima explosions per second. UN Secretary-General António Guterres has warned that “Earth is being pushed beyond its limits.”
Scientists said it was too early to determine whether the sea surface heating would prove temporary or worsen, as annual peaks are usually registered in July and August. However, 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.
