Climate change
THE world seems to be getting ever hotter, but how will we know when we have missed the target of limiting global warming to 1.5°C? Just three individual years of high global average temperatures will be enough, anew analysis reveals.
In the 2015 Paris Agreement, almost every nation in the world signed up to an international treaty promising to limit any hike in global average temperatures to “well below” 2°C above pre-industrial levels, and to aim for just 1.5°C of warming.
Since then, the 1.5°C goal has become the focus of global climate ambition, even as continued greenhouse gas emissions make it unlikely it will be achieved. Human activities have already increased average global temperatures by 1.26°C above pre-industrial levels, with some years already coming close to 1.5°C of warming.
Most ways to calculate a breach of the Paris temperature limits rely on decades of data to discern the state of the climate in order to iron out short-term blips. This means we may only know a target has been missed 10 years after the fact.
But now, Lawrence Jackson at the University of Leeds, UK, and his colleagues have for the first time identified that temperature data for individual years can provide an indication the world has passed 1.5°C in almost real time. They combined analysis of historical temperature records with modelling data to predict future temperatures and yearby-year variation (Research Square, doi.org/mxnn).
“We’ve helped to throw a light on the relationship between annual temperature changes and the long-term Paris Agreement temperature change,” says Jackson.
If average annual temperatures run at or more than 1.5°C above pre-industrial levels for three years, whether those years are consecutive or not, it is almost certain the world has breached the lower goal of the Paris Agreement, says Jackson.
The first annual breach may already be imminent. Last year saw record-breaking heat, with average temperatures running 1.44°C above pre-industrial levels (see graph, right). That was in part due to a major El Niño event (see story, opposite). The extraordinary run of high temperatures has continued into 2024, with this April the hottest on record.
Meanwhile, the global average for the past 12 months is also the highest on record, running at 1.6°C above the 1850 to 1900 average, the period used to gauge the pre-industrial temperature. It is “conceivable” that 2024 could be the first year to breach 1.5°C of warming, says Jackson, leaving just two more years of breaches until the target is missed. Most climate models expect the 1.5°C threshold to be exceeded at some point in the early 2030s, unless the world makes fast,
