A global agreement to combat climate change will take force after support from European nations sent the accord across an important threshold, prompting US President Barack Obama to hail it as a "historic day" for protecting the planet.
European nations raised backing for the 2015 Paris Agreement to countries representing 56.75 per cent of world greenhouse gas emissions, above the 55 per cent needed for implementation, a United Nations website showed.
The deal will formally start in 30 days on November 4 - four days before the US presidential election in which Republican Donald Trump opposes the accord and Democrat Hillary Clinton strongly supports it.
China and the United States joined up last month in a joint step by the world's top emitters.
Obama called Wednesday "a historic day in the fight to protect our planet for future generations" and he told reporters on the White House Rose Garden: "If we follow through on the commitments that this Paris agreement embodies, history may well judge it as a turning point for our planet."
Germany, France, Austria, Hungary, Slovakia and Malta - European Union nations which have completed domestic ratification and account for about four per cent of emissions - formally signed up on Wednesday.
In total, 72 countries out of 195 have ratified the agreement, according to the UN website.
"Great job!" tweeted European Climate Commissioner Miguel Arias Canete.
It took eight years for the previous UN climate deal, the 1997 Kyoto Protocol, to gain enough backing to take effect. It obliged only rich nations to cut emissions and the United States stayed out of it.
UN studies project that average world temperatures are set to rise by 3 degrees or more by 2100, based on current trends. And this year is expected to prove the warmest since records began in the 19th century, beating 2015.
Obama hails ratification of climate deal
US President Barack Obama has called the ratification of the Paris climate accord - a threshold nations officially reached on Wednesday - an "historic day" in the fight against climate change.
"Today, the world meets the moment, and if we follow through on the commitments that this Paris agreement embodies, history may well judge it as a turning point for our planet," Obama told reporters in a brief statement in the White House Rose Garden.
