In September 2024, the Baltic Sea has experienced a marine heatwave recorded on the coast of Finland. This is the second heatwave of the year in the region, with the previous heatwave observed at the turn of May and June. Unusually high temperatures have been persisting for several weeks, exceeding the average sea temperatures by as much as 5°C in some stations.

Marine heatwaves are extended periods of unusually high sea surface temperatures in a specific sea- or ocean region. As global temperatures rise, marine heatwaves are becoming more frequent and intense, posing serious threats to marine life and ocean health.

ObsSea4Clim aims to improve the description and detection of marine heatwaves as one of the key focus areas of the project. As marine heatwaves can disrupt ecosystems, reduce biodiversity, and negatively impact coastal communities, it is particularly important to provide accurate analysis and monitoring of the events.

New tool for identification of ongoing heatwaves

Finnish Meteorological Institute (FMI), a partner at ObsSea4Clim, has just published a new tool to identify and classify ongoing marine heatwaves according to their intensity in the Baltic Sea.

With the help of this tool, daily assessment of the heatwave situation in the Northern Baltic Sea is possible. It compares real-time observations from temperature buoys with historical data from 1991–2020. A heatwave is considered to be in progress if the observed temperatures remain above the threshold for the highest 10 percent for five consecutive days. Events are then classified on a four-step scale depending on the magnitude of the temperature deviation. Since the temporal coverage of observational data is limited for many of the stations, reanalysis climatology is used for classifying the heatwaves. The reanalysis relies on a physical model that has been fine-tuned using observational data to ensure maximum accuracy.