The world has already warmed by about 1.2°C since pre-industrial times. Within the next four years, there is a 48 per cent chance temperatures could breach the 1.5°C threshold for the first time, according to the UK Met Office. At most, the world has nine years until breaching 1.5°C for at least one year is inevitable, .
It would be a totemic milestone. The 1.5°C target has become a guiding light for the climate movement, after it was included as a “stretch goal” in the 2015 Paris Agreement. In the document, the world’s nations promise to limit any global rise in average temperatures to “well below” 2°C and to strive for warming of no more than 1.5°C.
That inclusion of 1.5°C in the agreement – fought for by campaigners and small island states at risk of rising seas – focused scientific minds.
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In 2018, the Intergovernmental Panel on Climate Change published a report on the projected impact of exceeding the 1.5°C target, which warned that warming beyond this level would be far more damaging than first thought.
Suddenly, the 1.5°C goal was the only target in town. With the science clear that 2°C of warming would cause devastation to some of the world’s most vulnerable communities, 1.5°C became central to conversations of climate equity and justice, as well as global ecological and financial stability.
Politicians and business leaders developed “net-zero” targets designed to deliver carbon cuts in line with the 1.5°C goal. The UK hosted the COP26 summit in 2021 with the explicit aim of “keeping 1.5°C alive”. By 2021, .
In the eyes of many, limiting warming to 1.5°C has become the defining measure of success in the climate fight, even as many scientists privately warn that the goal has slipped out of reach.
With the first breach of the threshold, that sense of hope and urgency could come crashing down. The first breach would be temporary, probably driven by a short-term surge in temperatures due to a powerful El Niño climate pattern, or a blast of climate-warming water vapour from a volcanic eruption.
It won’t count as a failure of the Paris Agreement, as those temperature goals will be assessed based on the average temperature over a 20 to 30-year period. By 2030, it will become clear whether or not the world has made the emissions cuts necessary to limit warming to 1.5°C over the long term. Based on current pollution rates, that seems highly unlikely.
However, overshooting 1.5°C, if only for a year, would be a crushing development and the political fallout would be huge. World leaders would be accused of making empty promises and business leaders harangued for polluting the world in pursuit of profit.
In the face of failure, some might propose increasingly radical – and risky – options to save the planet, like geoengineering. Others might throw their hands up in despair and lean into populist anti-climate rhetoric, particularly in the face of escalating calls for climate compensation from vulnerable countries.
And for the climate movement, the sense of urgency that has energised activists the world over could dissipate. If 1.5°C is no longer possible, can they convincingly recreate the same momentum for a goal of 1.6°C, or 1.7°C?
When it comes to climate change, every fraction of a degree matters. But as the 1.5°C threshold looms ever closer with each passing year, what comes next is becoming a crucial question – one that those involved in climate action must start to grapple with.
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