(CNN)Siberia's prolonged period of unusually warm weather is an "alarming sign," according to climate change scientists.

Surface temperatures in Siberia were up to 10 degrees Celsius (18 degrees Fahrenheit) higher than average last month, making it the vast Russian region's hottest May since records began in 1979, according to research by the Copernicus Climate Change Service (C3S), a program affiliated with the European Commission. Siberia's warmer weather came as the world experienced its hottest May on record, the C3S findings show.