In 2023, the average global temperature was at least 1.5C higher than pre-industrial levels on about a third of the days.

Climate change’s most damaging impacts can be avoided by staying below that marker long-term.

Yet 2023 is “on course” to be the hottest year on record, and 2024 could be even hotter.

We’re reaching levels we haven’t reached before, says Dr Melissa Lazenby of the University of Sussex. As political leaders gathered in Paris in December 2015, they agreed to keep global temperatures “well below” 2C and to make every effort to keep them below 1.5C.

In the pre-industrial period, between 1850 and 1900 – before fossil fuels were widely used – the agreed limits refer to the difference between current global average temperatures and the pre-industrial periods.

Paris thresholds are not breached for a day or a week, but rather over a period of 20 or 30 years.

Currently, the long-term average warming stands at around 1.1C to 1.2C.

It is also important to note that the more often 1.5C is breached for individual days, the closer the world gets to breaching this mark long-term. As politicians signed the deal on the 1.5C threshold in December 2015, this happened for the first time in the modern era.

Over the years, the limit has been repeatedly breached, typically only for short periods of time.

During 2016, the world saw around 75 days above that mark, as a result of a strong El Nio event – a natural climate shift that tends to increase global temperatures.