Unprecedented temperature anomalies in September have put 2023 on track to be the warmest year on record, according to the latest monthly climate bulletin from the Copernicus Climate Change Service (C3S).

Copernicus routinely publishes monthly climate bulletins reporting on the changes observed in global surface air temperature, sea ice cover and hydrological variables. The findings are based on computer-generated analyses using billions of measurements from satellites, ships, aircraft and weather stations around the world.

September 2023 was the hottest month in terms of global temperature - the most anomalous warm month of any year in the ERA5 dataset, which dates back to 1940. 

Globally averaged surface air temperature anomalies relative to 1991–2020 for each September from 1940 to 2023. Data source: ERA5. Credit: Copernicus Climate Change Service/ECMWF.

The month as a whole was around 1.75°C warmer than the September average for 1850-1900, the preindustrial reference period. 

Surface air temperature of 16.38°C, 0.93°C above the 1991-2020 average for September and 0.5°C above the temperature of the previous warmest September, in 2020. 

The global temperature for January-September 2023 was 0.52°C higher than average, and 0.05°C higher than the equivalent period in the warmest calendar year (2016). 

For January to September 2023, the global mean temperature for 2023 to date is 1.40°C higher than the preindustrial average (1850-1900), putting it close to the goal to limit global warming to 1.5 C (2.7 F) above pre-industrial levels set in the 2015 Paris Agreement.

Samantha Burgess, Deputy Director of the Climate Change Service C3S said:

"The unprecedented temperatures for the time of year observed in September - following a record summer - have broken records by an extraordinary amount. This extreme month has pushed 2023 into the dubious honour of first place - on track to be the warmest year and around 1.4°C above preindustrial average temperatures. Two months out from COP28 – the sense of urgency for ambitious climate action has never been more critical.”

For Europe, September 2023 was the warmest September on record, at 2.51°C higher than the 1991-2020 average, and 1.1°C higher than 2020, the previous warmest September. 

The average sea surface temperature for September over 60°S–60°N reached 20.92°C, the highest on record for September and the second highest across all months, behind August 2023.

Antarctic sea ice extent remained at record low level

The data for September 2023 show Antarctic sea ice extent remained at a record low level for the time of year.  Both the daily and monthly extents reached their lowest annual maxima in the satellite record in September, with the monthly extent 9% below average. 

In the Arctic, daily sea ice extent reached its 6th lowest annual minimum while the monthly sea ice extent ranked 5th lowest, at 18% below average. 

September 2023 – hydrological anomalies

September 2023 saw wetter-than-average conditions along many parts of the western seaboard of Europe, including the western Iberian Peninsula, Ireland, northern Britain, and Scandinavia.

It was also wetter than average in Greece following extreme rainfall associated with storm Daniel; this event was also responsible for the devastating flooding in Libya.

Southern Brazil and southern Chile also experienced extreme precipitation events.

Drier-than-average regions included parts of Europe, the southeastern USA, Mexico, central Asia, and Australia, where the driest September on record was recorded.