A UN deal to limit warming to well below 2C from pre industrial levels is now international law, in what officials say is an historic day in efforts to tackle climate change.
Agreed by 195 countries last December, the treaty commits governments to delivering regular carbon reduction plans and directing more funding towards low carbon sources of energy.
So far, 192 countries have signed and 94 governments have formally ratified the pact, which required support from 55 countries covering 55% of global greenhouse gas emissions to go live.
In an article on Climate Home, UN climate chief Patricia Espinosa writes that 4 November will be the day governments “shut the door on inevitable climate disaster”.
Analysis: So the Paris climate deal enters into force – then what?
“The Agreement is undoubtedly a turning point in the history of common human endeavour, capturing the combined political, economic and social will of governments, cities, regions, citizens, business and investors to overcome the existential threat of unchecked climate change,” she adds.
Recent data from the World Meteorological Organisation suggests 2016 will be the hottest year on record.
Meanwhile the UN Environment Programme reported this week that planned emission cuts are far off levels required to limit warming to the Paris goal of well below 2C.
Under the agreement countries are obliged to deliver regular plans to cut greenhouse gas emissions, although national contributions are not themselves legally binding under the UN.
But according to Christiana Figueres, who steered the UN to last year’s agreement in the French capital, entry into force is a sign governments are “understanding of the risks of inaction”.
COP22 preview: US election result to dominate UN climate summit
That political will is likely to be tested as negotiations on how the deal will work start at the UN’s COP22 summit in Marrakech, Morocco this coming Monday, with the treaty rulebook set to be finalised in two years.
“We’re on a rapid timetable. We thought we’d have until 2020 to finish these negotiations, we’re going to try and accelerate that and make 2018 the year to advance that schedule,” said lead US climate envoy Jonathan Pershing in a media briefing on Thursday.
As those talks start, most of the world’s attention will be fixed on the race for the White House, with the prospect of climate sceptic Donald Trump winning office on the Tuesday likely to temper any celebrations.
The election and its potential impacts on the UN deal will be the “main focus” of week one of the COP22 talks, a UK government source said.
China has already warned against a new US administration rowing back on its commitments under the 2015 deal, but John Morton, climate advisor to president Barack Obama, dismissed those concerns.
“Obviously there is a great deal of interest internationally on what the election outcome will be – the candidates have very different views on climate – but what we have seen in recent months and years is a recognised inevitability of the transition to a low carbon economy,” he told media in a call on Thursday.
“The international business and policy community will continue to move forward and there is no question of commitment at policy levels to the letter, intent and spirit of the Paris Agreement.
“We will see countries continuing to move forward at a fast clip irrespective of what happens on Tuesday. I think the question will be how fast the US moves.”