Three individual years of high global average temperatures will be enough for scientists to conclude the 1.5掳C climate goal is lost, a new analysis reveals.
In the 2015 Paris Agreement, almost every nation in the world signed up to an international treaty promising to limit any rise in global average temperatures to 鈥渨ell below鈥� 2掳C above pre-industrial levels, and to aim for just 1.5掳C of warming.
Since then, the 1.5掳C goal has become the focus of global climate ambition, even as continued greenhouse gas emissions make it increasingly unlikely it will be achieved.
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Human activities have already increased average global temperatures by 1.26掳C above pre-industrial levels, with some years already coming very close to 1.5掳C of warming.
Most methodologies to calculate a breach of the Paris temperature targets rely on decades of data, meaning the world may only know a target has been missed around 10 years after the fact.
at the University of Leeds, UK, and his colleagues have for the first time identified that temperature data for individual years can be used to provide an indication the world has passed 1.5掳C in almost real time.
They combined analysis of historical temperature records with modelling data to predict future temperatures and year-by-year variation. 鈥淲e鈥檝e helped to throw a light on the relationship between annual temperature changes and the long-term Paris Agreement temperature change,鈥� says Jackson.
If average annual temperatures run at or more than 1.5掳C above pre-industrial levels for three years, whether those years are consecutive or not, it is almost certain the world has breached the goals of the Paris Agreement, says Jackson.
鈥淥nce you鈥檝e crossed the 1.5掳C threshold in your annual temperature changes on three occasions, it鈥檚 very likely that we will have crossed the Paris Agreement 1.5掳C level,鈥� he says.
The first annual breach may already be imminent. 2023 was a year of record-breaking heat, with average temperatures running 1.44掳C above pre-industrial levels. That was in part due to a major El Ni帽o event, a natural ocean phenomenon that affects global temperatures. The extraordinary run of high temperatures has continued into 2024, with April the hottest on record, the 11th consecutive month of record heat.
Meanwhile, the global average for the past 12 months is also the highest on record, running at 1.6掳C above the 1850 to 1900 average, the period used to gauge the pre-industrial temperature.
It is 鈥渃onceivable鈥� that 2024 could be the first year to breach 1.5掳C of warming, says Jackson, leaving just two more years of breaches until the target is lost.
Most climate models expect the 1.5掳C threshold to be exceeded at some point in the early 2030s, unless the world makes immediate, dramatic cuts to emissions.
at Imperial College London says the analysis, which hasn鈥檛 yet been peer reviewed, 鈥減rovides a very simple, easily explainable metric鈥� for judging an overshoot of 1.5掳C. 鈥淚t provides a relatively fast indicator to determine with high certainty that we have crossed the 1.5掳C global warming limit,鈥� he says.
, a researcher at both the University of Exeter, UK, and the Met Office, which is the UK鈥檚 national weather service, says the paper is 鈥渧ery interesting鈥�. But he suggests scientists should agree on one methodology to judge progress against the Paris Agreement, to avoid any technical arguments 鈥渄istracting鈥� attention from climate action.
Any breach of the Paris goals is likely to provoke a huge outcry, particularly from nations most imperilled by rising temperatures. , who has advised the UK government during international climate negotiations, says the ability to identify a breach of 1.5掳C in real time could 鈥渇orce a reckoning鈥� in international talks, intensifying disputes over issues such as climate reparations.
But she says the 1.5掳C target will remain as a 鈥減olitical slogan鈥� because many countries have shaped national climate targets around the goal. As a result, there may be more focus on carbon removal strategies, with the aim of bringing global average temperature rise back down to below 1.5掳C in the long term.
鈥淚 don鈥檛 think we will get away from 1.5掳C. I still think it will be an important part of the political conversation,鈥� she says. 鈥淏ut I think the texture of it will shift because it will be seen in a different light.鈥�
at Leipzig University in Germany says the paper takes a 鈥渘eat approach鈥�. However, he stresses 1.5掳C is an 鈥渁rbitrary target鈥� that is almost guaranteed to be breached. What matters more, he says, is to what extent the world can limit warming to below 2掳C. 鈥淓very tenth of a degree centigrade past this 1.5掳C threshold, that matters as much as this 1.5掳C threshold,鈥� he says.
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