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.
To be implemented, the 2015 Paris Agreement needed support from enough countries to represent at least 55 percent of the world’s greenhouse gas emissions.
Germany, France, Austria, Hungary, Slovakia and Malta signed up on Wednesday, bringing support for the agreement to 56.75 percent, 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," telling reporters at 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."
The six European Union nations that formally signed up have completed domestic ratification, and account for about four per cent of emissions.
In total, 72 countries out of 195 have ratified the agreement, according to the UN website.
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 predict that average world temperatures are set to rise by 3 degrees or more by 2100, based on current trends.
This year is expected to prove the warmest since records began in the 19th century, beating 2015.