The Mediterranean breaks records and exposes Catalonia to increasingly extreme weather events.
Sea level rise and sea temperature have been exceptionally high again this year, especially in summer.
BarcelonaWe've been recording heat records in the Mediterranean Sea for quite a few years, and 2025 is no exception. Extreme heat has left unprecedented levels in recent months, and this summer the high temperatures caused a new record for sea level rise. Specifically, on August 28, a temporary peak of 40 centimeters above the reference value for the years 1990-1995 was recorded in L'Estartit (Baix Empordà). A record never seen since records began.
This is the conclusion of a report published this Friday by Meteocat based on data from Josep Pascual, a meteorological observer in Estartit who has the most reliable and oldest data for the entire Mediterranean Sea. "This [sea level] rise is primarily driven by marine warming during the summer, associated with air temperatures that have been more than 2°C above average," explains Marc Prohom, head of climatology at Meteocat, in the report.
The expert points out that this has been the second warmest summer on record in Catalonia, which has led to a "significant thermal expansion" of water in the western Mediterranean. The 40-centimeter rise in sea level recorded this summer was a one-off peak, but it is estimated that since the 1990s the average level of the Mediterranean Sea has already risen between 10 and 11 centimeters.
"This measurement is a frame of a larger picture that reflects the progressive rise in sea level associated with the climate emergency," Pascual says in the report. He has been collecting sea level data weekly since 1990 using a tide gauge.
An increasingly warmer sea
The warming of the Mediterranean Sea continues unabated, and the latest example is the exceptionally high temperature of the first half of October. According to data obtained by Pascual, a sea surface temperature of 21.7°C was recorded in L'Estartit on October 8, 1.8°C above the reference climate average for the years 1998-2022.
And this figure has been no exception, as we are coming off a summer and September that also saw clearly above-average values and new sea temperature records. Of note was the 26.8°C measured on the sea surface in L'Estartit on July 18, a value around 4°C above the average for the years 1998-2022. This exceptional figure surpassed the record for this month set on July 23, 2023, when 26°C was recorded. "This high sea surface temperature has been repeated almost every month this year and favors the formation of extreme weather events, among other consequences," says Prohoms.
In this sense, warmer sea water can cause stronger and more violent storms in our country. This situation also favors autumn rains being more torrential and abundant when large low-pressure systems arrive with cold air at altitude and moisture-laden offshore winds. The latest example was in Terres de l'Ebre, where rainfall dumped between 200 and 300 l/m² in just a few hours, causing significant flooding and damage.