What happens if the 1.5C target for global heating is missed?
The world’s most ambitious climate target is under threat, both from physics and politics. But what would it mean for the planet and its inhabitants if humanity were to abandon the goal to limit global heating to 1.5C above preindustrial levels?
The inclusion of 1.5C (2.7F) was hailed as one of the great triumphs of the Paris climate agreement of 2015. Until then, international ambition had been limited to 2C (3.6F), much to the frustration of small island states and others on the frontline of climate disruption.
The lower target focused minds on the huge difference that half a degree makes, which was underlined by a special report three years later by the UN’s top science body, the Intergovernmental Panel on Climate Change (IPCC), which spelled out the growing risk of calamities beyond 1.5C and the urgent need to cut carbon emissions by almost half by 2030 to have any chance of preventing them.
The target was more a line in the sand than a cliff edge, but it is fast becoming a milestone on the road to climate perdition.
Eight years after Paris, the only real change has been in the severity of the climate crisis. Oil companies are racking up record profits and planning to expand production. Emissions have increased to record levels.
Boosted by an El Niño, global temperatures this year are higher than at any time in human history with devastating impacts on human mortality, ecosystem destruction and food supplies.
In the first 10 months of 2023, global heating was already running at 1.4C above preindustrial levels, and is likely to touch 1.5C in the near future.
But a single year is not enough to determine climate trends, and there is no agreed methodology for what benchmark should be used. The UK Met Office is proposing an indicator combining the last 10 years of global temperature data and projections for the next 10 years. Under this formula, the global warming level stands at 1.26C.
The speed at which 1.5C is approaching has shocked many climatologists. Several influential scientists say it will be years rather than decades before the most ambitious Paris target is breached.
“1.5C is deader than a doornail and anybody who understands the physics knows that,” James Hansen, a former Nasa climate scientist, recently told reporters.
This is a contentious statement. Other scientists disagree, including Michael Mann of the University of Pennsylvania, who said Hansen’s views were “very much out of the mainstream”.
No nation wants to go down in history for killing the world’s most ambitious climate target, but in deed, if not word, many are contributing to its demise.
“Keeping 1.5C alive is a top priority,” the Cop28 president, Sultan Al Jaber, insisted earlier this year.
But he has contributed to the wilful neglect of the target in his other role, as head of the United Arab Emirates national oil and gas company Adnoc, which is increasing production of fossil fuels at a time when the International Energy Agency says they should be phased out.
Some climate activists believe 1.5C has become a convenient fiction that satisfies a craving for hope while masking the brutal reality that the planet is on course to warm by 2.4-2.7C (4.3-4.9F) by mid-century, and well over 3C (5.4F) by 2100.
There are still many scientists and activists who want to keep fighting for 1.5C, even if there is overshoot. This is not just because it is a useful political target, but because it is a reminder that every fraction of a degree is a matter of life and death for humans and countless other species.
The Guardian asked five climate experts to explain the key differences between 1.5C and 2C.
Food, water and conflict
Drought, storms and flooding become more frequent and severe with each extra fraction of a degree of warming.
For example, the IPCC has calculated that an extreme heat event that would occur only once in a decade in a climate without human influence would happen 4.1 times a decade at 1.5C of warming, and 5.6 times at 2C.
Those worst affected are usually least to blame – the climate-vulnerable people living in countries with poor economies and weaker healthcare systems.
Seventy million more people in Africa are projected to suffer acute food security at 2C than 1.5C, according to Catherine Nakalembe, who heads the Africa programme of Nasa Harvest.
At the lower temperature, she said, computer models indicate severe drought is 30% less likely than at 2C in southern Africa, while in west Africa yields of maize and sorghum could be 40% to 50% lower at 2C than 1.5C. Water scarcity would also affect 50% fewer people at the lower target.
With greater food insecurity comes an increased risk of conflict and a greater incentive to migrate. Even at current levels, disasters are striking different parts of the continent in rapid succession, such as the dire drought that brought misery to much of east Africa in 2019, or the cyclone – named Idai – that devastated southern Africa the same year.
“I’m afraid things are only getting worse. These events wipe out entire livelihoods and happen so frequently that there’s no time to recover,” said Nakalembe. “Every fraction of a degree matters because it can make a big difference in the severity of the impacts of climate change.”