The event, hosted by France, Britain, Italy, Chile and the United Nations, will see heads of state and government from over 70 countries pledge to increase their efforts to curb the greenhouse gas emissions that fuel global warming.
Experts say commitments put forward by the international community have already improved the long-term outlook on climate change, making the worst-case scenarios less likely by the end of the century.
But wildfires in the Amazon, Australia and America, floods in Bangladesh and East Africa, and record temperatures in the Arctic have highlighted the impact an increase of 1.2 degrees Celsius (2.2 Fahrenheit) since pre-industrial times is already having on the planet.
The Paris agreement aims to cap global warming at well under 2C (3.6F), ideally no more than 1.5C (2.7F), by the end of the century.
Achieving this will require a phasing-out of fossil fuels and better protection for the world’s carbon-soaking forests, wetlands and oceans.
The United States, which quit the Paris accord under President Donald Trump, won’t attend the event at the federal level.
But several U.S.governors and business leaders, such as Apple’s chief executive Tim Cook, will take part.
President-elect Joe Biden has pledged to rejoin the pact and put the U.S.on course to reduce its emissions to net zero by 2050.