Earth's surface was warmer last month than during any September on record, with temperatures since January tracking those of the hottest ever calendar year in 2016, the institution said Wednesday.
Record warmth in 2020 happened in the months of January, May, and September with June and April virtually tied for first, reported the Copernicus Climate Change Service.
"There is currently little difference between 2020 and 2016 for the year-to-date," Copernicus Senior Scientist Freja Vambourg told AFP.
For the 12-month period through September, the planet was nearly 1.3 degrees Celsius above pre-industrial levels.
That is alarmingly close to the 1.5C threshold for severe impacts detailed in a major 2018 report by the UN's climate science advisory panel, the IPCC.
The Paris Agreement has enjoined nations to cap global warming at "well below" 2C, and 1.5C if feasible.
So far, Earth has warmed on average by one degree, enough to boost the intensity of deadly heatwaves, droughts and tropical storms made more destructive by rising seas.
Climate change driven by greenhouse gas emissions from burning fossil fuels has picked up pace in recent decades.
Nineteen of the 20 last years are the warmest since accurate readings began in the late 19th century.
Since the late 1970s, the global thermometer has crept up 0.2C every decade, according to EU data.
Temperatures in September were "exceptionally high" over northern Siberia, which — along with much of the Arctic Circle — has seen freakishly warm weather for months.
The previous month was brutal in the Middle East, with new high temperatures reported in Turkey, Israel and Jordan in line with being the warmest September on record.