In 2023, the temperatures of the Mediterranean Sea reached the highest thermal value since the beginning of modern records, with an increase in the average surface temperature of over 1°C in 25 years, a progressive increase since 2013 in the southern Tyrrhenian Sea, extending northwards, and the warming of the deepest layers, up to 800 metres. This is what emerges from the activities conducted by e INGV within the MACMAP project[1] and presented on the occasion of the 25th anniversary of the activity of detecting the temperature of the waters of the Ligurian and Tyrrhenian seas, along the Genoa-Palermo route, in collaboration with , the MSC Group ferry company. In addition to the increase in average surface temperature, the “thermal photography” of the Mediterranean, carried out in 100 campaigns during which over 3 thousand probes were launched, also highlights an increase in the deeper layers (100-450 meters: +0,4 - +0,6°C; 450-800 m: +0,3 - +0,5°C).
Furthermore, the analysis of the measurements shows that between 2013 and 2016 the warming was greater than 0,4 °C, followed by a slight decrease and a stationary period in the following years, and then it started to increase progressively again from 2021 until September 2023, when it reached its maximum. For an indication of the extent of the phenomenon, it is worth noting both the short time span in which this change occurred and the fact that to induce in the Tyrrhenian Sea the increase in temperature measured between 2015 and 2023 in the layer between 200 and 800 m deep, an amount of energy equal to tens of times the electricity consumption in Italy in a year would be necessary.
“The historical series of temperature data along the same route is crucial for climate studies because it allows us to evaluate its temporal evolution, highlighting possible variations and therefore understanding whether there has been warming or cooling along the water column in the monitored area over time,” explain the ENEA researchers, including Franco Reseghetti, who recently retired and personally carried out the campaigns.
"This collaboration is part of GNV's broader sustainability strategy through which we intend, among other things, to make our active contribution to preserving biodiversity and the marine ecosystem. In fact, we hope there will be a way to further strengthen this project by bringing it to the other routes operated by our Company in the Mediterranean. The long-term goal is to also use the data collected for ever better management of our ships by optimizing, for example, the maintenance of hulls and propellers", says Ivana Melillo, Head of Energy Efficiency at GNV.
"What will the near future hold? The indications of the available models lean towards a possible further increase in water temperatures, but the veracity of these forecasts can only be confirmed by the measurements that the actors of this twenty-five-year activity have every intention of continuing to carry out, starting with the hundredth campaign scheduled for next December", says Simona Simoncelli, researcher at the INGV.
MACMAP - A Multidisciplinary Analysis of Climate change indicators in the Mediterranean And Polar regions
figure - Progressive ocean heat content since the late 50s, based on the two data sets used in the study. The baseline is the average ocean temperature calculated over the period 1981-2010 and the difference from this value is shown. The blue bars indicate colder waters than the 1981-2010 average, while the red bars represent warmer waters. The top graph shows the results from IAP, the bottom from NOAA.
On the cover: Franco Reseghetti ENEA. Launch of an XBT probe into the sea. The probe falls due to the force of gravity. The tube is used to distance the point of impact with the sea surface of the probe from the wake caused by the ship. The black cable near the operator's hand connects the probe to the acquisition system managed by a laptop computer that records the resistance measured by the probe as it moves towards the seabed. This resistance is then transformed by the software into the temperature value of the water and this data is saved in a file, one for each probe launched.
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