... But have we not passed the 1.5C threshold already?
The year 2023 is on track to be the hottest on record. It brought the world's hottest July in 120,000 years, and September was also the hottest on record by a large margin.
The global average daily temperature was more than 1.5C more than the preindustrial average for roughly one-third of days in 2023. Needless to say, this was a record number of days above the 1.5C daily limit.
But there is a big difference between the global temperature on individual days, and the long-term average. The latter is what's meant when the 1.5C threshold is discussed in negotiations like COP28 -- 1.5C warming is an average figure over a decadal time scale. This is a hard thing to measure, says Allen, and we know the global decade-to-decade average to within about a tenth of a degree at best.
Just as if you look at individual days rather than long-term averages, if you zoom in on particular regions of the world, we can also see that the 1.5C is being breached on local and regional levels.
The Arctic has warmed nearly four times faster than the rest of the world since 1979. Africa, too, warmed by around 0.3C per decade between 1991 and 2020, faster than the global average and faster than the 0.2C per decade in the 30 years before that.
When might we pass 1.5C on our current track and how will we know?
Earlier in 2023, the IPCC calculated that by the mid-2030s there would be a 50% chance of the world commiting itself to a rise of 1.5C. However, a new analysis taking into account more recent data suggests we could reach this threshold sooner " as early as 2029. ...
