The North Atlantic experienced one of the most intense and prolonged marine heatwaves (MHWs) on record in 2023, according to a major new global study.

Researchers found that global MHWs in 2023 reached unprecedented levels in intensity, duration, and scale—covering 96% of the world’s ocean surface and lasting four times longer than historical averages. The North Atlantic stood out among the worst affected regions, alongside the Tropical Pacific, North Pacific, and Southwest Pacific.

The North Atlantic event, which began in mid-2022, persisted for a staggering 525 days—well over a year—making it one of the most prolonged heat anomalies in the region’s recorded history. The study, led by Tianyun Dong and colleagues, combined satellite data with high-resolution ocean reanalysis models (including ECCO2 data) to trace and analyse the drivers behind the 2023 events.

Marine heatwaves are extended periods of unusually high sea temperatures and pose serious threats to marine life, ocean health, and the economies that rely on them. In Irish waters and the broader North Atlantic, such warming episodes disrupt ecosystems, threaten fish stocks, and may even affect weather patterns on land.

The study identified several overlapping causes for the 2023 heat extremes, including reduced cloud cover (allowing more solar heating), weaker winds, and altered ocean currents. These regional triggers combined with broader global warming trends to drive the scale and severity of the North Atlantic event.

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