Record ‘fish-killer’ June twice as likely due to climate change

The hottest June on record, which caused ‘unprecedented’ fish deaths in rivers, was twice as likely to occur due to climate change, the Met Office has confirmed.

The average temperature for June 2023 hit 15.8C, 0.9C hotter than the joint previous record of 14.9C in 1940 and 1976, according to the forecaster’s provisional figures.

In total, 72 counties saw their hottest June since records began in 1884.

‘It’s officially the hottest June on record for the UK, for mean temperature as well as average maximum and minimum temperature,’ said the Met Office’s Mark McCarthy.

‘June started with a good deal of high pressure and temperatures initially around average for many, but once that subsided, warm, humid air began to influence temperatures, with 32.2C the highest temperatures reached.

‘What’s striking is the persistent warmth for much of the month, with temperatures widely into the mid 20s Celsius for many and even into the low 30s at times.’

Paul Davies, Met Office climate extremes principal fellow and chief meteorologist, added: ‘We found that the chance of observing a June beating the previous joint 1940/1976 record of 14.9C has at least doubled since the 1940s.

‘Alongside natural variability, the background warming of the Earth’s atmosphere due to human induced climate change has driven up the possibility of reaching record high temperatures.’

The unseasonal weather resulted in higher than average fish deaths, at levels generally seen later in the season.

‘The reports of the number of fish death incidents in rivers for this time of year has been unprecedented,’ said the Angling Trust’s head of freshwater Mark Owen, speaking to the BBC. ‘I would normally expect rivers to be affected later in the summer when it’s hotter and drier.’

Speaking to the BBC’s Today programme, John Ellis of the Canal and River Trust echoed Mr Owen’s words, and said: ‘It’s been an unprecedented month.

‘We’ve had more than 60 fish mortality incidents on 21 different canals up and down the UK, and to put that into perspective, in a typical year, we may see half a dozen incidents.’

Mr Ellis told the BBC the increase in incidents was down to a combination of factors.

‘When we have high water temperatures, that water then holds less oxygen than if it’s cooler.

‘Fish and other insects being cold-blooded, will also use up more oxygen. Added to that we had a very large number of thunderstorms across the UK from the South East right the way up to the North West, and associated with heavy thunderstorms are drops in air pressure, which in turn takes oxygen out of the water.

‘I’ve been in this job for 35 years and we’ve had lots of wet cold summers in my time, but we’re now seeing, on average, summers are certainly getting warmer and drier and [there are] more extreme weather events.’

In addition to a lack of oxygen, flash floods following dry spells can wash dried-up pollutants from vehicles on the road into streams, poisoning fish.

The Environment Agency has confirmed it had received more reports of fish deaths year-on-year.

It is not only fish suffering in the warmer weather. Speaking to the BBC, the Wildlife Trusts’ Ali Morse warned that plants wilting in the heat left bees, butterflies and other insects with less food available.

‘Every month seems to be the hottest, the driest, the wettest, or whichever record-breaking event it is,’ said Ms Morse. ‘If we have a one-off pollution event or a wildfire, then there is normally time for nature to bounce back, but now it seems to be continually pounded by extreme weather.’

The UK suffered a particularly cold and wet spring, while in Spain, temperatures hit 40C in April.

However, the UK is also witnessing a marine heatwave, which appears to have driven temperatures higher.

Met Office scientific manager Segolene Bethou said: ‘These settled conditions also contributed to a fast warming of the sea surface around the British Isles: a severe marine heatwave was declared mid-June. 

Provisional findings from the Met Office suggest this marine heatwave in turn amplified land temperatures even further to the record levels seen during the month.’

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