Record ocean heat signals institutional stress as El Niño intensifies

The European Union’s Copernicus Climate Change Service has confirmed that average global sea surface temperatures reached a record high of 21.1 degrees Celsius in August. This figure surpasses the previous benchmark of 21.09C established in March 2024, marking a significant shift in the trajectory of global oceanic heat.

The agency attributes this development to a rapidly intensifying El Niño event occurring against a backdrop of long-term human-caused climate change. Samantha Burgess, the strategic lead for climate at the European Centre for Medium-Range Weather Forecasts, described the situation as placing “unprecedented strain” on the world’s oceans. She noted that while El Niño adds heat to the system, it does so on top of decades of human-driven warming.

The timing of this record is considered particularly notable by Copernicus, as global ocean temperatures typically peak in March or April. The current record was set in August, suggesting that the underlying thermal dynamics are shifting. The World Meteorological Organization also anticipates that El Niño will strengthen in the coming months, with seasonal forecasts indicating the event could reach levels not seen for several decades.

Policy implications are significant, as long-term fossil-fuel-driven warming has already raised ocean temperatures by 0.8C. Copernicus warns that rising temperatures have far-reaching consequences for marine ecosystems and coastal communities. Warmer oceans contribute to sea-level rise through thermal expansion and increase the likelihood of marine heatwaves, which can damage coral reefs and seagrass beds.

These environmental changes threaten to disrupt food chains and impact industries such as fishing and aquaculture. Furthermore, the agency highlights that warmer oceans are less able to absorb carbon dioxide, thereby weakening one of the planet’s key defences against climate change. Higher ocean temperatures also supply more heat and moisture to the atmosphere, enhancing the potential for extreme weather events.

Jane Lubchenco, an oceanographer and former head of the US National Oceanic and Atmospheric Administration, characterised the finding as “very troubling.” She warned that an ocean this warm destabilises weather patterns and threatens food security, economic prosperity, and marine life, stating that a warmer ocean is not a friend to global stability.