Austria, Belgium, France, Germany, Poland and Switzerland have all experienced their hottest Septembers on record, with unseasonably high temperatures set to continue into October, in a year likely to be the warmest in human history. As 31C (88F) was forecast in south-west France on Sunday and 28C in Paris, the French weather authority, Météo-France, said September’s average temperature was 21.5C, between 3.5C and 3.6C above the norm for the 1991-2020 reference period. That made it the hottest September – by more than 1C – since records began in 1900, the meteorologist Christine Berne said, adding that in several regions, the deviation from the September average of the past three decades had exceeded 4C, sometimes 6C. “A great many” monthly records had been broken across the country during an “exceptional” month, Météo-France said, with the temperature average higher than in July and August, and heatwave alerts issued in September for the first time. Germany’s weather office, DWD, said this September had been the hottest since national records started, almost 4C higher than the 1961-1990 baseline, while Belgium’s 19C average temperature was also almost 4C warmer than the norm. David Dehenauw of the Belgian Royal Meteorological Institute said: “Here too, September was hotter than July and August, which has not happened since 1961. “Belgium has never experienced a month of September this warm.” Poland’s weather institute has also announced September temperatures were 3.6C higher than average, and the hottest for the month since records began more than 100 years ago, as have authorities in Austria and Switzerland. The unseasonably high monthly averages were boosted by an unprecedented heatwave in the first half of last month in which France recorded its highest ever September temperature of 38.8C in the centre-west département of Vienne. In southern Spain, meanwhile, where what is believed to be the highest September temperature ever recorded in Europe – 45.7C – was registered on 5 September at Montoro, near Córdoba, the mercury hit 35C this weekend. The EU climate monitor said in early September that global temperatures in the northern hemisphere summer were the hottest on record. The Copernicus Climate Change Service also expects 2023 to be the hottest year humanity has experienced. Scientists say climate change driven by human activity is pushing global temperatures higher, with the world at around 1.2C of warming above pre-industrial levels. The disruption to the planet’s climate systems is making extreme weather events such as heatwaves, drought, wildfires and storms more frequent and more intense. Météo-France’s Berne said heatwaves were also occurring outside the usual high summer months of July and August. “We’re seeing them in spring and September, even October, as modelled by the Intergovernmental Panel on Climate Change (IPPC),” she said.