Climate change: 2023 on track to be planet’s warmest year in history, after record September heat and hottest month ever in July

“Unprecedented” heat last month has marked this September out as the planet’s hottest ever recorded – by a considerable margin.

According to scientists, September was “the most anomalous warm month of any year” in records stretching back to 1940.

Global air surface temperature for the month was 16.38C – 0.93C above the 30-year average and 0.5C hotter than the previous warmest September, in 2020. 

Europe experienced even more extraordinary heat – 2.51C higher than the 1991-2020 average, and 1.1C above the 2020 high. 

Worldwide, the month was around 1.75C warmer than Septembers in 1850-1900, the pre-industrial period used as a baseline when measuring global warming. This is well above the internationally agreed 1.5C ‘safe’ limit for warming, and not far off the 2C ‘danger’ level.

The high September temperatures continue a trend that has been playing out for most of the year, with a series of record-breaking heatwaves in many parts of the world in previous months.

The year is firmly on track to be crowned the hottest yet globally, stealing the title from 2016 and 2020, which are tied in first place.

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Last month was the hottest September on record globally, with "extraordinary" high temperatures in may places – the UK experienced a heatwave during the month, bringing the year's hottest day and an unexpected extension to summer for Britons. Picture: Getty Images

Meteorologists have put the extremes down to climate change.

Samantha Burgess, deputy director of the EU-backed Copernicus 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 1.4C above pre-industrial average temperatures. Two months out from COP28 – the sense of urgency for ambitious climate action has never been more critical.”

Even the UK experienced an unusually warm September, with a heatwave that saw two records broken in a single day – September 9 was both the hottest day of 2023 and the latest hottest day of the year ever known.

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The month was the UK’s joint-warmest September on record in a series going back to 1884, according to provisional Met Office statistics. It was Scotland’s third-warmest, with an average mean temperature of 12.8C.

“This September’s temperature records are heavily driven by how significantly warm the first half of the month was,” said Met Office scientific manager Mark McCarthy.

“Not only did September have the hottest day of the year – something that has only happened on four previous occasions in our observations – but it also had seven consecutive days where temperatures were above 30C somewhere in the UK, which had never happened in this month in Met Office observations.”

The global temperature for January to September was 0.52C higher than average, and 0.05C higher than the equivalent period in the warmest calendar year. The mean temperature for the first nine months of the year is 1.40C higher than the pre-industrial average, just 0.1C below the Paris Agreement’s target warming limit of 1.5C.

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Even the oceans have been warmer than usual, with average sea surface temperature last month the highest on record for September and the second-highest of any month – behind August. El Niño conditions, which can drive up temperatures, continued to develop over the equatorial eastern Pacific.