In 2015, almost 200 countries signed a landmark agreement to combat climate change.
The Paris Agreement aimed to hold “the increase in the global average temperature to well below 2C above pre-industrial levels” while pursuing efforts to limit it to 1.5°C.
The world has changed a lot since leaders celebrated this historic agreement in Paris a decade ago. Ahead of COP30, UN Secretary General António Guterres conceded that a “temporary overshoot above 1.5 degrees, starting, at the latest, in the early 2030s, is now inevitable”.
Emissions have continued to rise and the world’s climate has continued to warm. Extreme weather events have become more intense and more frequent.
As the UN summit kicks off in Belém, Brazil, we take a look at how our climate has changed since the Paris Agreement was signed in 2015.
The warmest 10 years on record
The Copernicus Climate Change Service (C3S) and Copernicus Atmosphere Monitoring Service (CAMS) have compiled data revealing the climate and atmospheric changes that have defined this decisive decade.
The past 10 years, from 2015 to 2024, have been the warmest 10 on record. And, depending on what global temperatures are in November and December, 2025 is set to be either the second or third warmest on record.
“A decade after the Paris Agreement, the world is hotter than ever – every year since has ranked among the 10 warmest on record,” says Carlo Buontempo, director of C3S.
“It is now evident that the climate is shifting at a pace humanity has never experienced.”
For the first time ever, C3S says, it’s possible that the 1.5ºC threshold will be exceeded for three consecutive years.
How close are we to 1.5ºC?
In December 2015, during the signing of the Paris Agreement, data extrapolated from the Copernicus Global Temperature Trend application estimated that global warming had reached 1.04ºC above pre-industrial levels and would reach 1.5ºC by March 2042.
Today, based on data from September 2025, we are estimated to be 1.4ºC above pre-industrial levels, and current Copernicus trend data suggest the 1.5 °C threshold could be reached around 2029.
To put it another way, a decade ago in 2015, the projected deadline for reaching 1.5ºC was 27 years away. Now it is estimated that this threshold is just four years away, or 23 years closer.
The striking change, experts say, suggests that global warming has accelerated quickly in recent years.
While they don’t fully understand the rapid increase in global temperatures, it is clear that ever-growing concentrations of greenhouse gases in the atmosphere have worsened the situation. It has made the goal of keeping global warming below 1.5°C above the pre-industrial average more difficult to achieve.
Progress has been made, however.
In 2015, the UN Environment Programme’s emissions gap report – published around the same time the Paris Agreement was adopted – projected a “baseline” of around 4°C of warming by 2100.
According to the latest emissions gap report, the world is now heading for 2.8°C warming if countries implement their current climate policies and between 2.3 and 2.5°C if signatories to the Paris Agreement fully implement their national climate plans.
Emissions have continued to increase
Greenhouse gases have steadily risen since 2015, reaching a record high in 2024, according to the World Meteorological Organisation. It said this was the largest one-year increase since measurements began in 1957.
Since the Paris Agreement was signed in 2015, carbon dioxide concentrations in the atmosphere have increased by 5.51 per cent, according to data from CAMS and C3S. In December 2024, they reached 422 parts per million (ppm).
During the same period, methane concentrations increased by 4.86 per cent, reaching 1,897 parts per billion (ppb) in December 2024.
“From air pollutants to greenhouse gas concentrations, our atmosphere is perhaps the most direct and immediate indicator of every action we take,” explains Laurence Rouil, director of the Copernicus Atmosphere Monitoring Service.
“Over the past decade, CO2 concentrations have risen over 5 per cent, reaching their highest annual levels ever recorded.”
Rouil says that, though fossil fuel emissions accounted for almost 75 per cent of total carbon emissions in 2024, wildfires also released more than 1,300 megatonnes of carbon in 2025 and huge amounts of particulate matter, which degrades air quality and has a harmful impact on human health.
Extreme heat has become more likely
Extreme heat has already become more likely since 2015, according to a separate joint report from Climate Central and World Weather Attribution.
On average, countries around the world have experienced 11 more hot days per year during the last decade than they did in the decade before the Paris Agreement.
The report looked at one particularly impactful extreme heat event from each of the six major continents as case studies.
Three of the six heatwave events they studied would have been nearly impossible without climate change – including the record-breaking 2023 heatwave in Southern Europe – and two were around 10 times more likely to occur in 2025 than in 2015.
A weeklong heatwave like the one in Southern Europe in 2023 is now 70 per cent more likely and 0.6°C hotter than it would have been a decade ago. Events like this were nearly impossible in a pre-industrial climate, according to the report.