How Detection Frameworks Shape Our View of 2024’s Mediterranean MHW

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Oceans absorb most anthropogenic heat and a large share of carbon emissions, driving sea surface temperature (SST) increases and intensifying marine heatwaves (MHWs). Although rising MHW frequency is well documented, most studies rely on the standard fixed‑baseline approach (Hobday et al., 2016), which uses a static climatology and is sensitive to long‑term warming, thereby amplifying recent extremes and raising concerns about future MHW “saturation” (Rosselló et al., 2023). To address these issues, we compare three detection frameworks—fixed baseline (1982–2011), 20‑year moving baseline (Rosselló et al., 2023), and a detrended method that removes the linear warming trend (Martínez et al., 2023)—across the Mediterranean Sea, a rapidly warming and ecologically vulnerable basin. Using SST data for 1982–2024, all three methods identify 2024 as the peak MHW year of the past two decades, with fixed and moving baselines also registering the longest‑lasting events. Regionally, the eastern Mediterranean, where warming is strongest, recorded the most MHW days in 2024, whereas the western basin experienced exceptionally intense events in 2022. Depending on the detection framework, estimated MHW exposure across the Mediterranean can vary by up to fourfold. Fixed baselines remain useful for assessing thermal stress relative to historical conditions, while moving and detrended methods better track anomalies in a changing climate. Aligning detection frameworks with research and policy goals is therefore crucial for reliable climate risk assessment and regional adaptation planning.

The research of this talk has been published on Ocean Science https://os.copernicus.org/articles/21/1987/2025/

Our speaker

Blanca Fernández‑Álvarez is a researcher at the IMEDEA CSIC and works with Ananda Pascual.

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