September 2023 was the hottest September ever recorded on Earth, according to a report issued by the Copernicus Climate Change Service on 5 October 2023, with an average global surface air temperature of 16.38°C, which is 0.93°C above the global average for September in the years 1990-2020, and 0.5°C higher than the previous hottest September ever recorded (September 2020). A 0.5°C increase over the hottest equivalent month is also a new record. The previous two months were the hottest August ever recorded and the hottest July ever recorded globally. This September was also 1.75°C warmer than the average for September between 1850 and 1900, taken as the pre-industrial reference period.
The average global temperature for the first nine months of 2023 (January-September) was 0.52°C above the average for the period 1990-2020, and 0.05°C higher than the previous highest ever recorded for this period in 2016. It was also 1.40°C higher than the average for the period 1850-1900.
Temperatures this September were particularly extreme in Europe, 2.51°C hotter than the average for the period 1990-2020, and 1.1°C hotter than the previous warmest ever September, in 2020. Many European countries recorded their warmest ever Septembers, with temperatures below the average for 1990-2020 recorded only in Iceland, Svalbard, Iberia, and Greece.
Exceptionally high temperatures were also recorded across much of Asia and Africa, with Sudan2, South Sudan, Ethiopia, and Eritrea particularly affected. Higher than average temperatures were recorded across much of North and South America, as well as Australia, with Western Australia recording its warmest ever September. Lower than average temperatures from the month were only recorded in parts of the western USA, southern Greenland, southern South America and Southern Africa.
Sea surface temperatures were also high, with the average sea surface temperature between 60°S and 60°N for the month being 20.92°C, the highest ever recorded in any September, and the second highest for any month ever, behind August 2023. Air temperatures over the ocean were also above average across much of the globe, driven by a developing El Niño system over the equatorial Pacific. High air surface temperatures were above average around the Antarctic, where sea-ice cover has been exceptionally low in 2023. Unusually mild temperatures were recorded across the southern parts of the Atlantic, Indian, and Pacific Oceans, although the temperature in the Wedel Sea was below average for the time of year, as was the sea around the southern tip of South America. Other areas of lower than average sea surface temperature were recorded off the west coast of Southern Africa, north-east of Iceland, west of Greenland, and south of Alaska.
The past twelve months (October 2022-September 2023) have been 0.46°C warmer than the average for 1991-2020, this joins three other twelve month periods (October 2015-September 2016, June 2019-May 2020, and July 2019-June 2020) as the joint warmest twelve month periods recorded.
The warmest full calender year ever recorded was 2016, when the global average temperature was 0.46°C above the average for the period 1990-2020, although 2020 came close to this, being 0.45°C above this average, while 2019 was 0.40°C above average, and 2017 0.34°C.
The first nine months of 2023 have been 0.52°C above the 1990-2020 average, making it the hottest year ever so far; for comparison the first nine months of 2016 were only 0.44°C above average. Temperatures are expected to remain significantly above average for the remainder of 2023, as the El Niño system over the Pacific continues to develop.
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