Hottest January on record sees the world reach 1.7°C warming mark

The temperature records keep on coming. This January was the hottest on record, at 1.7°C above the pre-industrial average for the month, according to the European Union’s Copernicus Climate Change Service.

This means there has been a 12-month period in which the average global surface temperature was more than 1.5°C above the 1850 to 1900 average, the period taken as the pre-industrial reference point.

“2024 starts with another record-breaking month,” said Samantha Burgess at the Copernicus Climate Change Service in a statement. “Rapid reductions in greenhouse gas emissions are the only way to stop global temperatures increasing.”

At the Paris climate meeting in 2015, countries pledged to try to stop the global temperature rising more than 1.5°C above pre-industrial levels. Climate scientists will not regard this limit as having been breached until the long-term average global temperature has remained above this level for a number of years.

At present, the long-term average is 1.25°C above that of pre-industrial times, according to Richard Betts at the Met Office, the UK’s national weather service. But with carbon emissions still rising, it seems certain that, on this measure, the 1.5°C limit will soon be breached, probably around 2030.

The long-term global average is rising in line with the projections of climate models. However, the extremely rapid warming in the past year or two has far surpassed expectations. Among other records, 2023 saw the first day that was more than 2°C warmer than the 1850 to 1900 average.

It remains unclear why there has been such rapid warming in the past year or so and for how long it will continue. Possible factors that might have enhanced warming include the Tonga volcano eruption in 2022 injecting large quantities of water into the stratosphere and a reduction in aerosol pollution from ships.

Climate scientists have defined the pre-industrial temperature as the 1850 to 1900 average for practical reasons, as there are few temperature records before this. But using this as the baseline may mean that the level of warming due to fossil fuel emissions is being underestimated.

One 2017 study suggests that we have got it wrong by around 0.2°C. Another out this week, based on an analysis of sea sponges, puts the discrepancy at 0.5°C, meaning that the 1.5°C limit has already been breached – but other climate scientists aren’t convinced.