September 2023 was the warmest September on record, with an average surface air temperature of 16.38 degrees Celsius, 0.93 degrees above the 1991-2020 average for the month, according to the European Union-funded Copernicus Climate Change Service.
This makes the last four months of the year the hottest on record, with 2023 on track to be the warmest year ever.
The average surface air temperature in September 2023 was also 0.5 degrees Celsius higher than the previous warmest September, in 2020, according to the Copernicus Climate Change Service (C3S), which is implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF).
C3S said the month as a whole was around 1.75 degrees Celsius warmer than the September average for 1850-1900, which is frequently used as a benchmark for the preindustrial period.
The global temperature for January-September was 0.52 degrees Celsius higher than average, and 0.05 degrees higher than the equivalent period in 2016 — the warmest calendar year.
During January to September, the global mean temperature was 1.40 degrees Celsius higher than the preindustrial average (1850-1900).
Scientists say the last four months have been extraordinary in terms of global average temperatures, with new monthly records set every month and often by a large margin.
Researchers at Berkeley Earth, an independent US-based non-profit organisation, said the longer recent period of warmth is driven by a combination of several man-made and natural factors acting together.
Firstly, man-made global warming has been raising the Earth’s temperature by about 0.19 degrees Celsius per decade. This is a direct consequence of the accumulation of additional greenhouse gases, especially carbon dioxide, in the atmosphere. This is the primary factor responsible for long-term warming, Berkeley Earth said.
However, global warming is a gradual process. It does not explain short-term spikes and fluctuations in the Earth’s average temperature. The main reason for such spikes is internal variability in the distribution of heat and circulation of the oceans and atmosphere, it said.
The largest and most well-known form of short-term internal variability is the El Niño/La Niña cycle originating in the Pacific. During the El Niño phase, global average temperatures tend to be slightly higher. As a result, record highs for global average temperature tend to be set during El Niño years. This year, a new El Niño officially began in June after a three-year La Niña period, it said.
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