Climate change dramatically reshapes the ocean conditions, manifested by ocean warming that extends from surface to subsurface waters across all ocean basins. Marine heatwaves (MHWs) are becoming more frequent, intense, and long-lasting across European seas. They are only partially predictable, and highly disruptive to
marine ecosystems, coastal communities, and ocean-based economies, requiring urgent integration into EU climate adaptation and marine policy frameworks. Scientifically, MHWs remain insufficiently understood and monitored, particularly when it comes to their subsurface manifestation and evolution.

To inform emerging European and international policy frameworks, ObsSea4Clim developed a dedicated policy brief on marine heatwaves, targeting European policymakers – including those contributing to the Ocean Act – and international organizations such as the World Meteorological Organization.

The policy brief is available here: https://zenodo.org/records/21032889

Our key policy recommendations related to marine heatwaves are:

• Establish a scalable and standardised MHW indicator framework for European seas, which is guided by the context of the impacts and ensures comparability and policy usability.
• Establish a future-proof, sustainable, and resilient ocean observing system under the frameworks of Global Ocean Observing System and the Ocean Act that fully addresses the ocean observation requirements for the early detection, monitoring, and warning of marine heatwaves across all European seas.
• The Subsurface Ocean Temperature Essential Ocean Variable should be integrated in the Global Basic Observing Network (GBON) as recommended by the Joint Collaborative board between WMO and IOC.
• Ensure broad access to Ocean Best Practices for monitoring and data management to support the required observational coverage, data quality, and data security.
• Support the development of an integrated multipurpose observing system that takes optimal advantage of platforms and new technologies. Such efforts are needed in order to deliver the suite of Essential Ocean Variables required for evaluation of multi stressors on the marine environment and ecosystem.
• Invest in Artificial Intelligence (AI) systems and coupled ocean-atmosphere models to improve seasonal and subsurface prediction skill and early warning for ecosystems in the coastal zone.

The policy brief “Europe’s Warming Seas” was presented at the European Maritime Days 2026.