Global sea surface temperatures have reached record highs for this time of year – the latest sign that the world’s oceans are entering what scientists describe as “uncharted territory”.
On 21 June, the global average reached 21.0°C, according to measurements taken by both the Copernicus Climate Change Service (C3S) and the Copernicus Marine Service (CMEMS). This beats the previous records from 2023 (20.83ºC) and 2024 (20.86ºC) by 0.1°C.
Although it might appear marginal, even tiny temperature shifts can wreak havoc on marine ecosystems, contribute to sea level rise and trigger extreme weather events.
While the onset of El Niño conditions in the Equatorial Pacific on 2 June has contributed to the record-breaking reading, it is part of a longer-term trend driven by climate change. Rising ocean temperatures outside the polar regions have been between 0.35ºC and 0.73ºC higher over the last three years compared with the long-term average, according to Copernicus.
Related“Current conditions could indicate the beginning of a new phase, leading, once more, to uncharted territory,” says Carlo Buontempo, Copernicus Climate Change Service Director at the European Centre for Medium-Range Weather Forecasts (ECMWF).
“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.”
It’s a warning that echoes recent UN projections, which found a 91 per cent chance that at least one of the next five years will exceed the 1.5°C warming threshold which the Paris Agreement warned the Earth should not surpass. The UN also predicted an 86 per cent chance that one of those years will surpass 2024 as the hottest on record.
What is the impact of a warmer ocean?
The impact of rising sea surface temperatures isn’t confined to the oceans. By heating up the atmosphere, warm oceans provide extra energy to storms and increase evaporation, which can lead to heavy rainfall and flooding.
Ocean warming also contributes to sea level rise and ice melt, and stresses marine ecosystems.
It can also contribute to more frequent and intense marine heatwaves, which disrupt ecosystems and fisheries, affect coastal economies and can intensify extreme heat on nearby land.
RelatedEl Niño worsens this by adding further heat into the atmosphere, increasing global temperatures and shifting weather patterns across the globe.
Climate scientist Friederike Otto of Imperial College London, who was not involved in the Copernicus analysis, has warned that any extended period above 1.5°C threatens “a whole range of extreme weather events that exceeds anything we’ve experienced in the past” – and that many cities remain unprepared.
Otto has also warned against placing too much emphasis on the natural El Niño phenomenon’s role in worsening global weather extremes: “It comes and goes. Climate change on the contrary gets worse as long as we do not stop burning fossil fuels,” she said in May.
Copernicus scientists are continuing to monitor the situation to assess whether the new high is temporary or longer-lasting.
