The UK is among more than 160 countries set to sign up to the world's first comprehensive deal to tackle climate change at a ceremony in New York.
But environmental campaigners in the UK are criticising the Government for continuing to back fossil fuel extraction at home despite supporting the international climate deal to drive down greenhouse gases.
The Paris Agreement to curb rising temperatures and avoid "dangerous" climate change was secured at United Nations talks in the French capital in December.
An official ceremony at the UN in New York will see more than 160 countries and the European Union sign up to the deal on Friday, the first day it is open for signing - Earth Day.
A handful of countries will also ratify the agreement, and there is a push for nations to follow suit as soon as possible so the deal can come into force quickly.
At least 55 countries covering 55% of the world's emissions need to ratify the deal for it to become official.
While Energy Minister Lord Bourne is attending the ceremony to sign the agreement for the UK, the Government faces criticism at home for continuing to allow mining for coal, the dirtiest fossil fuel.
Friends of the Earth climate campaigner Guy Shrubsole said: "To meet the Paris Agreement, the Government must leave fossil fuels, like coal, in the ground - yet we're still permitting vast new opencast coal mines to be dug up next door to communities and beauty spots across the UK."
He urged ministers to leave coal in the ground.
The Paris Agreement sets a target to keep temperature rises "well below" 2C and commits to strive to curb increases to 1.5C, as well as a five-year review system to increase ambition on cutting emissions to meet the temperature goals.
Greenpeace UK executive director John Sauven said: "The world leaders in New York today will be judged not on the brilliance of their rhetoric but on the boldness of their actions.
"David Cameron's government did the right thing by phasing out coal, but the next generation won't judge him kindly if it keeps undermining clean energy and subsidising fossil fuels."