A long-lasting marine heat wave hit the waters surrounding the United Kingdom and Ireland in spring 2025.
A long-lasting marine heat wave hit the waters surrounding the United Kingdom and Ireland in spring 2025. By mid-May, sea surface temperatures in some areas reached up to 4 degrees Celsius (7 degrees Fahrenheit) warmer than normal. The heat wave began in early March and continued into May, according to the U.K. Met Office, making it one of the region’s longest on record for this time of year.
Persistent high-pressure weather systems throughout the spring produced long spells of sunny, dry, and calm weather—ideal conditions for surface waters to warm, experts noted. Heat from the Sun can build up quickly in the topmost layer of water when winds and waves are too calm to churn up cooler water from below. Throughout April and May, surface water temperatures reached the highest values in satellite records going back to 1982. These conditions followed a winter where sea surface temperatures were already above average.
This map shows temperature anomalies across the water’s surface on May 22, 2025. The values reflect how far temperatures differed from the 2003-2014 average for that day. By this time in the heat wave, temperatures in the North Sea had already peaked, while surface waters west and south of Ireland were hitting some of their highest temperatures of the event so far.
Read More: NASA Earth Observatory
Photo Credit: NASA Earth Observatory/Wanmei Liang
