What is the Paris Agreement and why does 1.5C matter?

In Paris in 2015, almost 200 countries signed a landmark agreement designed to limit global warming to 1.5C and avoid its worst impacts.

But despite some progress in areas like renewable energy, the world has continued to warm at a rapid pace.

A recent UN report said the target was likely to be breached in the next few years and that “urgent and stringent” action would be needed to return the world to 1.5C.

What is the Paris climate agreement?

The Paris Agreement is at the heart of the international commitment to tackle rising global temperatures.

It came into force on 4 November 2016 and saw almost all the nations of the world agree to cut the greenhouse gas emissions which cause global warming.

However, the United States – the world’s second biggest greenhouse gas emitter – withdrew from the deal in January 2026 under President Donald Trump.

The US also withdrew during Trump’s first presidency, but it rejoined in 2021 under his successor President Joe Biden.

The only other UN member states outside the Paris agreement are Iran, Libya and Yemen.

What does the Paris Agreement say?

The Paris 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, generally considered to mean the late 19th Century

• 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 a 20-year average rather than a single year.

So, while 2024 was more than 1.5C warmer than pre-industrial times, it did not mean the Paris Agreement threshold has been breached.

Why does keeping global warming to 1.5C matter?

Every 0.1C of warming brings with it greater risks for the planet, such as longer heatwaves, more intense storms and wildfires, according to climate scientists.

But a very large body of scientific evidence shows that warming of 2C or more would bring far greater impacts, on top of those felt at 1.5C, UN scientists say.

These include:

• more people being exposed to extreme heat
• higher sea levels as glaciers and ice sheets melt
• increased risks to food security in some regions due to more extreme weather
• greater chances of some climate-sensitive diseases spreading, such as dengue
• more species being threatened with extinction
• the loss of virtually all coral reefs

Some changes could become irreversible if so-called “tipping points” are crossed.

It is not clear exactly where these sit, but once these thresholds are passed, changes could accelerate and become irreversible.