NEA IRAKLEIA, Greece, Nov 4 (Reuters) - Strolling along the coast of Nea Irakleia village where he would go swimming as a young man, George Perperis points to where there was once a beach, now submerged by seawater. "Here was a 20 metre-wide beach that has completely vanished," says Perperis, 59. "Families would gather here for a swim and fishermen would lay their nets." Accelerating coastal erosion due to climate change pose an existential threat to places such as Nea Irakleia in western Halkidiki, a three-pronged peninsula of lush forests and golden sands in northern Greece that lives off tourism. The region was one of those worst-hit by the financial crisis that ravaged Greece from 2010 to 2018, shrinking the economy by a quarter and tipping many into poverty. Now the impact of rising temperatures, freak weather and accelerating coastal erosion on key sectors such as tourism and agriculture could again jeopardise the finances of Europe"s most indebted country. "The crisis years were really difficult, a lot of stores closed and tourism tapered off. Then there was COVID," said Perperis, a retired mechanic and local community leader. "But climate change might be worse. What will a tourist do here if there is no beach left?" Experts say coastal erosion at Halkidiki, which attracts about 10% of Greece"s annual 30 million visitors, has intensified in the recent years. An observatory set up two years ago in Thessaloniki, monitors the phenomenon using satellite photos, sea floats and algorithms. Eighteen areas that authorities call "red points" have been identified in the region, showing intense coastal vulnerability. "Unfortunately we can see regions where we will have serious problems across the coastline," said Costas Gioutikas, vice-prefect for the environment in central Macedonia. "We see beaches literally vanish." MEETING THE COST Before the pandemic, tourism accounted for about a fifth of Greece"s economy and a similar proportion of jobs, earning revenue of 18 billion euros in 2019. Economists warn that the challenges posed by climate change - freak weather patterns, tides flooding beaches, scorching summers and a decline in rainfall - could all pose a significant drag on Greece"s growth potential. Research by Greece"s Central Bank from 2009, the most recent available, showed the cost of inaction on climate change to Greece"s economy topping 700 billion euros by 2100, representing a 2% drop in national output every year. It said adaptation action could reduce the cost by 30%, and mitigation policies by a further 30%. An updated report will be ready in a few months. With a public debt estimated at 196.6% of GDP, Greece is the most indebted economy in the euro zone, making it vital that the country can sustain growth to keep up repayments. "It is important to realise that Greece should be at the forefront of countries that initiate mitigation policies," said Stavros Zenios, a professor at the University of Cyprus and a non-resident fellow at think-tank Bruegel. "For countries like Greece the expected GDP growth rate could drop to one-third by the end of the century of what it is today." Yannis Stournaras, Greece"s Central Bank Governor, told Reuters that the country"s finances were manageable. Interest payments on its mountain of debt - most of it refinanced at very low rates of around 1.5% - translate to less than 3% of national output annually. Growth rates should exceed borrowing costs to keep a lid on that debt, Stournaras said. But, as world leaders meet in Glasgow for the COP26 global climate conference, he said he worried that not enough was being done to tackle the most damaging effects of global warming. "It is not only a theory or an academic issue, it is with us now and I am afraid the world is not doing enough," said Stournaras. "The horizon is so distant that nobody thinks we should take action now to solve what will mostly appear 50 years from now." SCORCHING DAYS, FREAK WEATHER This summer Greece has already seen a glimpse of what a warmer future may bring, with thousands of hectares of forest burning for days in wildfires that tore through the outskirts of Athens and other areas. read more Working on a scenario of a 2.5 degrees Celsius rise by 2046-2065, compared with 1971-2000, a team at the University of Athens predict that heatwave days - defined by at least 3 days over 40C - will increase by 15-20 days annually by 2050, while rainfall will decrease by 10% to 30%. Scientists warn that sea levels could rise by 20 to 50 cm (8 to 20 inches) in the same period. This could render Greece"s 16,000-km (9,940-mile) coastline vulnerable as one-third of the population lives at a distance of up to 2 km from the coast and 90% of the country"s tourism infrastructure sits on coastal areas. Increasingly, bursts of extreme weather are also expected. On the night of July 11, 2019, at least seven people were killed and more than 100 hurt from a violent, short-lived "supercell" storm that lashed an area not far from Nea Irakleia. "Of course its all linked to the disturbances to the climate," said Christos Zerefos, a professor at the Academy of Athens and a climate expert. "If nothing is done to stabilise the climate such phenomena will only continue, and increase in coming years." Writing by George Georgiopoulos; Editing by Alex Richardson