Sea temperature of 18.7C sets new record

The data, recorded by Guernsey Sea Fisheries, showed a high of 18.7C on 7 September – 0.3 higher than August the previous year.

But while the warm seas may be welcomed by the island’s swimmers, it could have long-lasting effects on the Bailiwick’s marine life.

Sea fisheries officer Simon Hall said that sea temperatures for the last two or three summers had seen an increase of roughly 1C to 1.5C on summer averages, whereas winters had been more ‘normal’.

‘We have seen anecdotal evidence from the UK with similar trends,’ he said.

‘And this has effectively seen marine species moving north in search of cooler waters.’

Sea Fisheries has recorded local temperatures at St Peter Port since 1980.

Guernsey Met Office senior meteorological officer Adam Heaume said the convention was to use a 30-year averaging period when comparing climate data, and Guernsey’s records were not extensive enough to show if this was conclusive proof of climate change.

‘If you compared mean annual temperature, the temperature over the last 10 years was about 1C warmer than it was in 1980s,’ he said.

‘While our dataset is limited, eight of the last 10 years have seen sea temperatures above the long-term average.

‘For 2023, the mean annual temperature was 0.5C above the 1991-2020 average.

‘Although this doesn’t necessarily give the full picture, with the first half of the year trending slightly colder than average, with a rapid warming around May and June.’

UK Met Office published data last June that showed that global sea surface temperatures for both April and May were the highest since records were first taken in 1850.

In the report it stated that these temperature increases were driven by a combination of human-caused climate change and natural variation of the climate system.

The Guernsey Met Office will be publishing its annual report for 2023 in the coming months, which includes further statistics on the trend for rising sea temperatures.