The world has moved closer to warming by more than 1.5C, as new data shows 2024 was the planet's hottest year on record.
To avoid some of the most damaging impacts of climate change, nearly 200 countries had agreed to try to keep long-term temperature increases below this level.
Scientists say that every 0.1C of temperature increase brings with it greater risks for the planet, such as longer heatwaves, more intense storms and wildfires.
The 1.5C target was agreed because there is very strong evidence that the impacts would become much more extreme as the world gets closer to 2C. Some changes could become irreversible.
The science is not completely certain, but the consequences of 2C global warming versus 1.5C, external could be:
Extreme hot days would be on average 4C warmer at mid-latitudes (regions outside the poles and tropics), versus 3C at 1.5C
Sea-level rise would be 0.1m higher than at 1.5C, exposing up to 10 million more people to more frequent flooding
More than 99% of coral reefs would be lost, compared with 70-90% at 1.5C
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In 2015, world leaders pledged to try and prevent global temperatures rising by more than 1.5C above those of the late 19th Century – known as "pre-industrial" levels.
It saw almost all the world's nations agree to cut the greenhouse gas emissions which cause global warming.
Adopted by 194 parties (193 countries plus the EU) in the French capital on 12 December 2015, the Paris Agreement came into force on 4 November 2016.
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The agreement lists a series of commitments:
To "pursue efforts" to limit global temperature rises to 1.5C, and to keep them "well below" 2.0C above those recorded in pre-industrial times
To achieve a balance – known as net zero – between the greenhouse gases that humans put into the atmosphere and the gases that they actively remove, in the second half of this century
Each country to set its own emission-reduction targets, reviewed every five years to raise ambitions
Richer countries to help poorer nations by providing funding, known as climate finance, to adapt to climate change and switch to renewable energy
The 1.5C target is generally accepted to refer to the 20-year average, rather than a single year.
So, while the year 2024 was more than 1.5C warmer than pre-industrial times, that does not mean the Paris Agreement threshold has yet been breached.
World leaders meet every year to discuss their climate commitments, at international summits known as COPs (Conference of the Parties).
All COPs since 2015 have tracked how countries are building on what they promised in Paris.
When the agreement was signed, governments admitted the Paris targets would not limit global warming to 1.5C.
Current climate plans still put the world on track for around 2.6C to 2.8C of warming by 2100, according to the UN. But this could drop to 1.9C if all net zero pledges were achieved, meaning countries need to put in place more policies to achieve their goals.
At COP28 in December 2023, countries agreed for the first time to "contribute" to "transitioning away from fossil fuels", although they were not forced to take action.
But there was no significant progress at COP29 in November 2024.
Many countries – including Canada, New Zealand and some island states – said the agreement reached at the summit was too weak, and watered down the previous years' pledges.
The Paris deal restated a commitment first made in 2009 that the world's richer countries should provide $100bn (around £81bn) annually by 2020 to help developing nations deal with the effects of climate change, and build greener economies.
In 2020 only $83.3bn was raised, and the goal was eventually achieved in 2022, according to data from the OECD, external.
In 2023 countries agreed for the first time that a fund should be established exclusively for loss and damage. This is money to help countries recover from the impacts of climate change.
At COP29 countries agreed to update the 2020 goal.
Richer nations committed to providing $300bn (around £244bn) a year to developing nations by 2035, with a broader ambition for $1.3trn to be raised from private and public sources by the same date.
However, developing countries – which had hoped for more – criticised the $300bn figure as a "paltry sum".
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