Marine extreme events, encompassing phenomena such as storm surges, marine heatwaves, biogeochemical extremes, harmful algal blooms, jellyfish blooms, extreme storms, and even unique occurrences like medicanes (Mediterranean hurricanes), are becoming more common. These events have profound consequences for marine ecosystems, coastal communities, and global economies. Extreme sea level events, driven by intense storms and rising sea levels, can inundate coastlines, leading to devastating flooding and erosion. Marine heatwaves, fuelled by climate change, can trigger mass coral bleaching events, disrupting delicate marine ecosystems and jeopardizing the biodiversity that they support. Harmful algal blooms and jellyfish blooms, exacerbated by nutrient pollution and warmer waters, can lead to oxygen depletion, cause mass mortality events in various species, and pose risks to human health. The concurrence of oceanic and atmospheric extremes, marine and atmospheric heat waves, wind and wave extremes, harmful algal blooms, hypoxic conditions, and high-acidity events may lead to a nonlinear increase in environmental stress.

Addressing the impacts of these events requires a comprehensive approach, involving measures to mitigate climate change, improve coastal resilience, and promote sustainable marine management practices. A crucial aspect of addressing and mitigating the impacts of marine extreme events lies in deepening our scientific understanding of these phenomena and in establishing solid methodologies for defining climatological baselines and for extreme analyses in a changing climate. Scientific research plays a pivotal role in unravelling the intricate mechanisms behind these events, predicting their occurrence, and formulating effective strategies to manage and adapt to their consequences. By exploring the underlying causes, interactions, and feedback loops, scientists can provide invaluable insights that guide policymakers, communities, and industries in making informed decisions.

The 55th Liége International Colloquium was dedicated to ocean extremes and motivated this special issue. We welcome all submissions in any of the above-mentioned topics, regardless of the authors’ participation or presentation at the 55th International Liége Colloquium.