Kiev records warmest autumn in 140 years
Average temperatures reached 11.6 degrees Celsius, which is 3.6 degrees Celsius above the norm, the observatory said in a statement.
"Autumn in 2020 was the warmest since 1881," it said.
Ukraine has been hit by unprecedented heat waves this year, fuelling fires that are difficult to bring under control.
Scientists predict that climate change will increase the frequency and severity of extreme weather events such as catastrophic fires.
Fires in April ravaged more than 66,000 hectares (14.8 acres) in the exclusion zone around Chernobyl in northern Ukraine, the scene of one of the world's worst nuclear accidents in 1986.