October 15, 2023

2023 Had Warmest September on Record Globally; Set to be Warmest Year

Sandipan Talukdar

C3S bulletin revealed September 2023 was 1.75 degrees Celsius warmer than estimated value for September; Report also says September’s temperature record showed global temperature anomalies more positive than any month in any year in ERA5 dataset

AUTUMN this year appeared not to be so pleasant. On the contrary, the world witnessed the hottest September on record globally, that too by a record-breaking margin. September’s high temperature comes along with the hottest conditions that prevailed in the northern hemisphere during this summer.

The Copernicus Climate Change Service (C3S) bulletin revealed the shocking realities of global warming conditions, where it said that September this year turned out to be the warmest one ever recorded. According to it, the average surface air temperature was 16.38 degrees Celsius, around one degree (0.93) Celsius above the average temperature from 1991-2020 for September. Again, this temperature deviates by half a degree Celsius above the previous warmest September recorded in 2020. 

September 2023 was 1.75 degrees Celsius warmer than the estimated value for September of the period 1850-1900. Notably, this period is the designated pre-industrial reference period. Again, the period 1991-2020 is considered the baseline for ‘using as a practical tool for climate-sensitive sectors like agriculture’, according to the United Nations (UN). 

The C3S report also says that September’s temperature record showed global temperature anomalies more positive than any month in any year in the ERA5 dataset. Temperature anomaly means the departure from a reference point or long-term average; a positive anomaly indicates an increase in the temperature in comparison to the reference value. The C3S produces the ERA5 dataset and is the ‘fifth generation ECMWF (European Centre for Medium-Range Weather Forecasts) atmospheric reanalysis of the global climate covering the period from January 1940 to present’.  This clearly states that September has been the warmest month ever since the recording of temperature began in 1940. 


The deputy director of C3S, Samantha Burgess, termed the year 2023 to be receiving the dubious honour of being the warmest year. In a statement, Burgess was quoted to have 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.” 

WMO Terms it an Ominous Signal, Will Produce its Global Climate Report at COP28

World Meteorological Organisation (WMO) has called the September extreme temperature an “ominous signal about the speed with which greenhouse gases are changing our climate.” “The year 2023 is now on track to be the warmest year on record. Numerous high-temperature records have been broken in recent months,”—it wrote in its release. 

“Since June, the world has experienced unprecedented heat on land and sea. The temperature anomalies are enormous – far bigger than anything we have ever seen in the past. Antarctic winter sea ice extent was the lowest on record for the time of year. What is especially worrying is that the warming El Niño event is still developing. So we can expect these record-breaking temperatures to continue for months, with cascading impacts on our environment and society,” commented Petteri Taalas, secretary-general of WMO, in a comment. 

WMO will produce its provisional report on the State of the Global Climate in 2023 at the start of the climate summit COP28 in November, to be held in Dubai this year, combining the ERA5 dataset of C3S and other leading international datasets.

January-September 2023: Higher Global Average Temperature

The C3S also said that in the first nine months of 2023, from January to September, the average global temperature is higher by 0.52 degrees Celsius compared to the average value of 1991-2020. It was also higher by 0.05 degree Celsius than the first nine-month average of 2016; thus, 2023 becomes the ‘warmest calendar year on record’ as C3S has termed. 

Again, for 2023, the global average temperature for the first nine months is 1.40 degrees Celsius, higher than the pre-industrial average temperature, that is, during the period 1850-1900. 

Earlier, C3S termed August to be the hottest month on record as the global mean temperature for the month was 0.7 degrees Celsius higher than the 1991-2020 value. The year 2023 also had the hottest summer on record, from June to August. 

Sea Ice Content Remained at a Record Low

Antarctic sea ice extent also remained at a record low level this year. During September, the monthly extent remained 9 per cent below the average per satellite records. On the other hand, the monthly Arctic sea ice extent went 18 per cent below the average, which is the fifth lowest. 

Experts opine this record is alarming and further calls for urgent actions to be planned at the climate summit COP28 in November in Dubai. Countries will meet to formulate action plans towards meeting the goals set in the Paris Agreement of limiting the global temperature rise to 1.5 degrees Celsius above the pre-industrial level.