September temperatures around the world were the warmest on record for the month, breaking the previous record by a wide margin, according to the EU's climate service.
Last month was 0.93C warmer than the average September temperature between 1991-2020 and 0.5C warmer than the previous record set in 2020.
Experts believe that continued greenhouse gas emissions, in addition to El Nino, are driving the heat.
Some scientists said they were shocked by the news.
September's high comes on the heels of the hottest summer on record in the Northern Hemisphere, as rising temperatures show no sign of abating.
The data show that the month had the largest deviation from the long-term average in records dating back to 1940.
"This month was, in my professional opinion as a climate scientist, a story," wrote Zeke Hausfather, in X.
"The unprecedented temperatures for the time of year observed in September, following a record summer, have broken extraordinary records," says Samantha Burgess, Deputy Director of the Copernicus Climate Change Service (C3S).
Extreme heat has continued into October, breaking monthly high records in many countries as experts say global temperatures could rise further above normal.