One of the most extreme marine heatwaves ever recorded is currently affecting the waters of the Baltic Sea and around the coasts of Britain and Ireland, according to a press release issued by the European Space Agency on 20 June 2023. The Baltic Sea is currently 8°C above the annual average for June, based upon data from the years 1981-2016, while the North Sea is currently 5°C above average, with the northwest coast of the UK between Durham and Aberdeen particularly affected.
Sea surface temperatures on 18 June 2023, relative to average June temperatures for the period 1981-2016. European Space Agency.
Marine heatwaves tend to be closely linked to other extreme weather events, typically causing these to be longer and more intense, with the two systems potentially creating a feedback loop in which each system intensifies the other. They are also often associated with mass deaths of Fish and other marine organisms, as warmer water is capable of retaining less dissolved oxygen than cool water.
This event is part of a trend of rising ocean and atmospheric temperatures, with the global average sea surface temperature in both April and May being the highest ever recorded in those months, according to the UK's Met Office, which has temperature records going back to 1850.
These high sea temperatures are linked to other extreme weather events which have been affecting the planet this year, including the fires sweeping across the forests of Canada, the heatwaves being experienced in many parts of the world, and a sharp reduction in the levels of sea ice around Antarctica.
June 2023 looks likely to be another record-breaking month, with the Copernicus Climate Change Service reporting that the first 11 days of the month each saw the hottest global average temperatures recorded for that date, and average global temperatures exceeding pre-industrial temperatures by 1.5°C, the first time this has ever happened in June.
While the high temperatures in the North and Baltic seas are expected to be a temporary event, further high temperature events are expected in the coming months, driven by an emerging El Niño system in the South Pacific, with predictions currently indicating that 2024 will be the hottest year ever recorded.
El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.
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