September was the warmest on record globally, according to the weather service Copernicus.
It was 0.05C hotter than September last year, which in turn set the previous record high for the month.
Scientists say it’s a clear indication of temperatures being driven up by emissions from human society.
Copernicus, which is the European Union’s Earth observation programme, said warmth in the Siberian Arctic continues way above average.
And it confirmed that Arctic sea ice is at its second lowest extent since satellite records began.
This year is also projected to become the warmest on record for Europe, even if temperatures cool somewhat from now on.
The elevated heat globally contributed to record wildfires in California and Australia.
It also helped fuel the hottest day on record – a searing 54.4C (130F) in Death Valley.
And it had a hand in the torrential downpours that inundated the south of France with more than half a metre of rain in a day.
Météo-France, the French met office, said a downpour like this was expected once in 100 years – they had two in a month.
Samantha Burgess, deputy director of the Copernicus Climate Change Service, told BBC News: “Some of these events are extraordinary – although we mustn’t create a false expectation that temperatures will go up year on year.
“Climate and weather are highly variable. But we predicted that these sort of events would happen, given our effect on the climate.”
Weather records are always being broken naturally, but meteorologists say they’re disturbed by some of the new extremes.