Italian National Agency for New Technologies, Energy and Sustainable Economic Development
Environment: ocean 'fever' reached a new record in 2023
The 'ocean fever' is still rising. In 2023 seawater temperatures increased, recording a new record in water warming, with an increase in heat content, stratification and salinity. This is what emerges from the New Record Ocean temperatures and related climate indicators in 2023 article, published in the journal Advances in Atmospheric Sciences. The analyses were conducted by an international team, coordinated by IAP-CAS (Institute of Atmospheric Physics of the Chinese Academy of Sciences) and composed of American scientists mainly from the NCEI-NOAA (National Centers for Environmental Information of the National Oceanic and Atmospheric Administration), New Zealanders, French and, for Italy, by Simona Simoncelli of the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and Franco Reseghetti of the National Agency for new technologies, energy and sustainable economic development (ENEA).
In 2023, the temperature of ocean waters, which cover 70% of the planet and absorb about 90% of the heat caused by global warming, increased by a value between 9 (according to NOAA calculation) and 15 (IAP-CAS calculation) ZettaJoule compared to 2022 in the layer between 0 and 2000 meters deep, where 1 ZettaJoule is equivalent to double the amount of energy that powers the world economy every year. The different results seem to be mainly attributable to the different data quality control procedures and calculation methodologies.
In addition to the general warming of the marine waters, very strong anomalies were also found in the sea surface temperatures, with unexpected values attributable in this case not only to global warming, but also to the short-term thermal fluctuations of the Pacific Ocean due to the transition from La Niña to El Niño phenomena, starting from May 2023.
The overall warmer waters produced by the combination of these factors can change weather patterns worldwide. In particular, the variation in atmospheric precipitation and the evaporation of surface waters alter the ocean salinity, so that salty areas continue to become more and more salty and areas with fresher water continue to decrease their salinity, with direct consequences about marine life, ocean currents and interactions with the atmosphere.
Less dense, warmer and less salty waters tend to remain on the surface and are unable to transport heat, carbon dioxide and oxygen to deeper waters, with serious consequences for animal and plant life in the ocean. In this case, we are talking about "stratified" waters: according to the study just published, in the last year stratification has also increased further compared to 2022.
Due to warmer ocean waters, excess heat and moisture enter the atmosphere due to evaporation of surface waters, allowing storms to become more violent, with stronger rain and winds and, therefore, with a greater risk of flooding, even on Italy.
In this global scenario, the Mediterranean Sea in 2023 confirmed itself as the fastest warming basin among those analyzed in the study, reaching the highest thermal value since the beginning of modern records.
“In 2023, INGV and ENEA continued, as part of the MACMAP project financed by INGV, to collect sea temperature data on a seasonal basis, in particular along the Genoa-Palermo route in the Ligurian and Tyrrhenian Seas, thanks to the collaboration with the Grandi Navi Veloci (GNV) shipping company”, explains Simona Simoncelli, INGV researcher and co-author of the study. The analysis of these temperature data, as well as those collected at 400 meters deep by the CNR-ISMAR mooring in the Sicily Channel, indicates a clear warming in the layer between 150 and 450 meters depth since 2013, which extended to deeper (up to 700 meters) waters and northward. In this case between 2013 and 2016 the warming was above 0.4 °C, followed by a slight decrease and a stationary period. The water temperature has started to increase again in 2021, reaching its new record in September 2023".
“A systematical monitoring of the seas, namely the Mediterranean Sea, by measuring the values of some parameters such as temperature, salinity, PH and oxygen, is the only way to consolidate knowledge on the subject and improve the reliability of the forecasts that at the moment are not as accurate as necessary and desired, but there is a clear trend of temperature growth", adds Franco Reseghetti, ENEA researcher and co-author of the study.
“The Mediterranean strongly influences life in the countries bordering it: from agriculture, to fishing, hydrology, weather evolution, the health of populations and so on. Continuing to monitor it is the key to understanding the effects of global warming, raising awareness about this emergency and stimulating the adoption of necessary adaptation and mitigation measures. We must always keep in mind that due to this phenomenon enormous damages occur every year all over the world, often accompanied by the loss of human lives", conclude the researchers.
Figure 1 - Progressive ocean heat content since the late 1950s, based on the two datasets used in the study. The reference line corresponds to the average ocean temperature calculated for the period 1981-2010, The difference with this value is reported. Blue bars indicate colder waters than the 1981-2010 average, red bars represent warmer waters. The upper graph shows the results of the IAP, the lower one of the NOAA.
Figure 2 - Total variation in sea surface temperature (Sea Surface Temperature - SST) from 1955 to 2023, obtained from the analysis of data (1 m) of the first level of the IAP/CAS grid. The black line represents the annual value and the red line the monthly value. Anomalies relate to the reference period 1981-2010. The annual change in SST is shown in the inner panel, with 2023 values shown in black.
Figure 3 - Temperature along the MX04 Genoa–Palermo transect (western Mediterranean) recorded with XBT probes launched from ships of opportunity and monthly mean temperatures taken 400 m from the Sicilian Channel buoy. (a) XBT traces in the Tyrrhenian Sea and the Ligurian Sea. (b) Hovmöller plot of mean MX04 temperature anomalies over the period 1999–2023, calculated by subtracting the 1981–2010 baseline of IAP/CAS data. (c) MX04 mean temperatures calculated in the 100–700 m layers, and monthly mean temperatures taken 400 m from the Sicilian Channel buoy between 2004 and 2023, with error bars representing the relative standard deviations.
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