These last few months have been marked by several record temperatures, both in the air and in the oceans. July was another historic milestone, with new temperature highs. During this critical period, which saw heat waves in various parts of the world, such as the Mediterranean, Portugal was spared, both in terms of temperatures felt on land and in maritime records. There are two main reasons, closely linked: anticyclone of the Azores and the phenomenon of coastal upwelling.
After a month of June that was very hot and dry, Portugal escaped the heat wave that devastated Southern Europe in July. Alessandro Marraccini, meteorologist at the Portuguese Institute of the Sea and Atmosphere (IPMA), then explained to the PUBLIC that the positioning of the Azores anticyclone caused mainland Portugal to be hit by fresh air masses coming from the north.
The oceans have also seen an unprecedented increase in temperature since spring. The global average surface temperature reached 20.9 degrees Celsius (ºC) in July, about half a degree above the average value from 1991 to 2020, according to a report from the National Climate Service. Climate Change of the European Copernicus program. In the North Atlantic, the waters were 1.05ºC above average for the month. However, similar to what happened with the atmospheric heat wave, Portugal did not record abnormally high temperatures in the waters off the continental coast.
According to data from the Copernicus Marine Environment Monitoring Service (CMEMS) collected and analyzed by PÚBLICO, July was a month of descent and stabilization of sea surface temperatures on the coast of mainland Portugal. The main reason is the phenomenon of coastal upwelling, or upwellingwhich occurs due to the movement of air masses coming from the North, explains Isabel Iglesias, researcher at the Interdisciplinary Center for Marine and Environmental Research (Ciimar) in the area of physical oceanography.
This oceanographic phenomenon is characterized by the displacement of surface waters caused by the wind, which leads to an “upwelling of deeper, colder waters”. The situation is normal in the summer months, being associated with the typical north wind felt on the beaches of the west coast of Portugal – a north-northwest wind that is related to the Azores anticyclone.
Isabel Iglesias states that the phenomenon has still occurred without change, despite the increase in global temperature and other changes that have occurred.
“It can be more or less intense, more or less prolonged, but that is why here in Portugal we do not see this temperature anomaly at the coast for now”, continues the researcher, adding that the scientific community does not know how climate change could affect the upwelling.
“Climate change is not just about warming seawater. It will produce changes in wind patterns and, producing these types of changes, can produce changes in the intensity of the upwelling”, he says, highlighting the importance that this phenomenon has for Portugal.
“THE upwelling is extremely important for fisheries. In addition to the cold water, it brings nutrients from the bottom, which become suspended again in the upper water layers. We wouldn’t have sardines if there weren’t upwelling”, he warns.
In addition to the coastal outcrop, Isabel Iglesias points out other factors, such as the mouths of rivers and the currents very typical of local circulation, due to the coast – which is the reason why this type of analysis is usually carried out on a larger scale, at the level of ocean basins.
Records on the Portuguese coast
Although I am not following the galloping rise observed in the North Atlanticthe surface sea water temperature on the Portuguese coast reached record values in the first half of 2023: the year began with historic records for the month of January, followed by an end of 2022 with high temperature values for the season. In June, the 24th had an average temperature of 20.3ºC, the highest record ever for that month since 1993, the year in which the Copernicus historical database begins.
The first three weeks of July, although below global records of the North Atlanticwere above the average temperature from 1993 to 2021. Only a short period in mid-May and a few days in July and August saw sea temperatures drop below the calculated average value.
“There have always been years that were warmer and others that were colder, both in terms of the ocean and the atmosphere. It has to do with the balance of the Earth system itself”, says Isabel Iglesias. But this variability does not remove urgency from the issue of climate change: “Climate change is there, and it is something we we should worry. The heat waves we’ve had lately are not normal, nor are the extreme events what we are witnessing.”
