Recent trends of SST in the Western Mediterranean basins from AVHRR Pathfinder data (1985–2007)

Climate change in the Mediterranean region cannot be understood without taking into account changes in the Mediterranean Sea, which is an important source of moisture and heat for the Mediterranean climate system. Many research papers have been published in the last two decades increasing our knowledge about long-term trends and inter-annual variability of temperature and salinity in the Western Mediterranean. Although recent changes have been better documented, there remain uncertainties because different results are obtained depending on the period of time analyzed or the geographic region selected. This paper analyses the regional, seasonal and decadal variability of sea surface temperature in the Western Mediterranean basins (Northern (Ligurian Sea and Gulf of Lions), Balearic, Algerian and Alboran) by means of thermal satellite images. Monthly data from the PO.DAAC (Physical Oceanography Distributed Active Archive Center) have been processed for the period 1985–2007. Results show an averaged warming linear trend of 0.03 °C/yr. This rate is higher during the spring (0.06 °C/yr) in all the basins and the highest values were registered in the Northern basin in June. The study suggests that an early warming of the Sea is occurring in all the basins during the spring, with an increment of 0.5–1 °C in the mean SST of April, May and June over the two decades studied. The analysis of thermal anomalies confirms the warming trend with a dominance of negative anomalies during 1985–1996 and a dominance of positive anomalies during the last decade (1997–2007). Intense anomalies are more frequent in the Northern basin.

► SST variability in Western Mediterranean has been analyzed from NOAA images
► A warming trend of 0.03 °C/yr has been registered for 1985–2007
► The highest warming rate occurs during the Spring season (0.06 °C/yr)
► Over the two decades analyzed the onset of summer has moved forward.
► Mean SST of April, May, June and July have increased nearly 1 °C during the two decades