Britain is anticipating a complex autumn season, with experts warning that the lingering effects of a record-breaking summer heatwave, coupled with the influence of a developing Super El Niño, could lead to a less vibrant display of fall foliage and increased rainfall. The unusual summer temperatures, which peaked in the high 30s Celsius, have caused some deciduous trees to shed their leaves prematurely, a phenomenon known as 'false autumn,' a stress response to extreme heat and drought.
This early leaf drop means that the vibrant reds, deep browns, and mellow yellows typically seen in autumn may be less widespread. Kevin Martin, Head of Tree Collections at the Royal Botanic Gardens, Kew, explained that following the hottest summer on record, the usual widespread blaze of autumn color might not materialize all at once. He noted that many trees, particularly in the south of England, have already lost their leaves early. Martin added that while this year's display is more complicated, some individual trees might still offer strong colors in October, and certain species could even exhibit more impressive shows than usual.
The 'false autumn' phenomenon serves as a warning sign about the increasing pressure on trees from a rapidly changing climate, according to Martin. He highlighted that while autumn color is beautiful, it also reflects the health of the trees, which are long-lived organisms facing growing challenges.
Adding to the unpredictable autumn forecast is the Super El Niño, a naturally occurring climate phenomenon characterized by the warming of sea surface temperatures in the central-eastern Pacific. Current sea surface temperatures in this region have already surpassed those recorded during the strong El Niño of 2015. Experts predict that this Super El Niño could contribute to milder, wetter, and stormier weather in the UK in the coming weeks and into early winter.
Meteorologists have noted that unseasonably warm weather, with temperatures climbing back into the mid-20s Celsius in London, is possible due to high pressure drawing warm air from the south. However, this is occurring against a backdrop of human-caused climate change, which has elevated background temperatures, making warm weather patterns more intense. A rapid attribution study by the Met Office found that this year's record-breaking summer was made significantly more likely by climate change resulting from the burning of fossil fuels.
While El Niño has a strong influence on tropical weather patterns, its direct impact on the UK's weather systems is considered weaker and less consistent, with the Atlantic and the jet stream playing a more dominant role in shaping British autumn weather. Nonetheless, the developing El Niño is expected to contribute to above-average global temperatures in the coming months and into next year.