Paris: A worldwide pact to battle global warming entered into force Friday, just a week before nations reassemble to discuss how to make good on their promises to cut planet-warming greenhouse gases.
Dubbed the Paris Agreement, it is the first-ever deal binding all the world's nations, rich and poor, to a commitment to cap global warming caused mainly from the burning of coal, oil and gas.
"A historic day for the planet," said the office of President Francois Hollande of France, host to the 2015 negotiations that yielded the breakthrough pact.
"Humanity will look back on November 4, 2016, as the day that countries of the world shut the door on inevitable climate disaster," UN climate chief Patricia Espinosa and Moroccan Foreign Minister Salaheddine Mezouar said in a joint statement.
Mezouar will preside over the UN meeting opening in Marrakesh on Monday.
"It is also a moment to look ahead with sober assessment and renewed will over the task ahead," they said.
This meant drastically and urgently cutting emissions, which requires political commitment and considerable financial investment.
The urgency was brought home by a UN report Thursday warning that emissions trends were steering the world towards climate "tragedy".
By 2030, said the UN Environment Programme, annual emissions will be 12 to 14 billion tonnes of carbon dioxide equivalent (CO2e) higher than the desired level of 42 billion tonnes.
The 2014 level was about 52.7 billion tonnes.
2016 is on track to become the hottest year on record, and carbon dioxide levels in the atmosphere passed an ominous milestone in 2015.
The Eiffel Tower in Paris as well as public buildings in Marrakesh, Adelaide, Brussels, New Delhi and Sao Paulo were to be lit in green to mark the entry into force of the pact meant to stop the rot.
That historic agreement was finally endorsed in the French capital last December, after years of complex and divisive negotiations, but the ratification was reached with record speed.
At least 55 parties to the UN's climate convention (UNFCCC), responsible for at least 55 per cent of global greenhouse gas emissions, had to ratify it for it to take effect.
It passed the threshold last month, and by today had been ratified by 97 of the 197 UNFCCC parties, representing 67.5 per cent of emissions, according to France's environment minister Segolene Royal, the outgoing president of the UN talks.
"It is a magnificent day, concluding years of hard work," Royal told journalists in Paris.
"We must maintain this extraordinary momentum by encouraging countries to continue ratifying the deal, and by moving full steam ahead with our preparations to put it into action across the world," Europe's climate commissioner Miguel Canete added in a statement.