A Swiss weather balloon had to climb to an unprecedented 5,300 metres (17,400ft) before the temperature fell to 0C (32F), meteorologists have said, as a late summer heatwave and wildfires continue to pummel swaths of continental Europe. A man was found dead in a blaze raging north of Athens on Monday as the Greek government warned of an extreme risk of fire across the country, while more than half of mainland France was placed under an amber extreme heat alert and local records tumbled in the south-east. MétéoSuisse said the zero-degree line – the altitude at which the temperature falls below freezing, considered a key meteorological marker particularly in mountainous regions – was measured at 5,298 metres overnight. The figure, which was registered by a weather balloon flown from Payerne in western Switzerland, constituted “a record since monitoring began in 1954”, the service said, and surpassed the previous high of 5,184 metres that was “only set in July last year”. The 0C line “affects vegetation, the snow line and the water cycle, so has a considerable impact on the habitats of humans, animals and plants alike”, MétéoSuisse said. It averaged 2,570 metres above sea level from 1991 and 2020, fluctuating between 1,000 and 2,000 metres in winter, and 3,000 and 4,000 metres in summer. In recent decades “anthropogenic climate change has caused the altitude of the zero-degree line to rise significantly in every season”, the service said, noting that successive records for the indicator had all been set in the past 10 years. Experts have said an exceptional area of high pressure across continental Europe centred over the Alps has created a heat dome that is forecast to push temperatures to record or near-record levels in several regions until at least Wednesday. In Greece, a shepherd who tried to save his animals was found dead as a fire raged near Boeotia, about 60 miles (100km) north of Athens. People on a beach and in two communities near the blaze were ordered to evacuate, AFP reported. Another wildfire broke out on the island of Evia on Monday and at least four more were raging in north-eastern Greece in the regions of Rodopi and Kavala, Aspropyrgos west of Athens, and north-east Greece near the port city of Alexandroupolis, where 13 communities were evacuated over the weekend. The EU said it was deploying two Cyprus-based firefighting aircraft and a Romanian firefighting team via the bloc’s civil protection mechanism amid what it called “by far Greece’s worst summer” for wildfires since 2008. Civil protection authorities warned of an “exceptional” fire risk in the region around Athens and other parts of southern Greece. “We are facing extreme phenomena,” a fire service spokesperson said, urging people to follow authorities’ instructions. In Spain, the state weather agency, Aemet, has placed five provinces in the southern region of Andalucía on amber heat alert, warning that temperatures are forecast to rise to more than 40C around Seville, Córdoba and in the Guadalquivir valley. In the Canary Islands, 600 firefighters were making progress, however, battling an out-of-control blaze on Tenerife that was started deliberately and has forced more than 12,000 people to flee their homes and burned through more than 12,800 hectares (31,600 acres) of land, about 6.5% of Tenerife’s surface area. The prime minister, Pedro Sánchez, said during a visit to the island that he hoped better conditions would “help us declare the fire as stabilised in the coming hours, coming days. The next few hours are going to be very important.” Spain has suffered 340 fires so far this year, which have ravaged almost 76,000 hectares, EU figures show. In France, record temperatures of more than 42.5C were recorded along the Rhône valley and at several other south-eastern weather stations, with the mercury set to rise further on Tuesday and Wednesday. Fifty of the country’s 96 mainland departments were on amber heat alerts, with some expected to be placed on a maximum red warning over the next few days. After weeks of dry weather, local authorities in Gard département restricted access to forests due to the high risks of fires, while firefighters were battling a blaze near the village of Chanousse in the south-east that had so far consumed about 120 hectares (296 acres) of forest. The highest temperature ever recorded in France was 46C, registered in June 2018 in the village of Vérargues in southern France.