World leaders have agreed at the UN headquarters to ratify the Paris climate deal and get the ball rolling on plans to check global warming.
Held on Earth Day, Friday's ceremony in New York City came four months after the deal was clinched in Paris and marks the first step towards binding countries to the promises they made to cut greenhouse gas emissions.
"The era of consumption without consequences is over," UN Secretary-General Ban Ki-moon said on Friday.
"We must intensify efforts to decarbonise our economies. And we must support developing countries in making this transition."
French President Francois Hollande and Canada's Justin Trudeau joined John Kerry, US secretary of state, for the signing ceremony attended by 175 governments, the largest single-day signing of an international agreement.
Kerry carried his granddaughter in his arms, a symbol of the future generations the agreement is aimed at protecting.
While the US, China and India - the world's top greenhouse gas emitters - were not represented at their highest level, leaders of island states such as Fiji, Tuvalu and Kiribati, facing existential threats from rising sea levels, were to present formally the already completed ratification by their parliaments.
"China will finalise domestic legal procedures on its accession before the G20 Hangzhou summit in September this year," China's Vice Premier Zhang Gaoli said at the signing ceremony.
Last month was the hottest March in modern history and 2016 is shaping up as a record-breaking year for rising global temperatures.
This year's El Nino - dubbed Darth Nino - is believed to be behind droughts, floods, severe storms and other extreme weather patterns.
The Paris agreement will come into force as soon as 55 countries responsible for 55 percent of the world's greenhouse gases have ratified the accord.
The target date for the agreement to begin is 2020.
China and the US have said they will ratify this year and are pushing for quick ratification so that the agreement becomes operational possibly as early as late 2016 or 2017.
Caught in the midst of an election campaign, the US plans to ratify the Paris accord with an executive agreement, bypassing Congress and setting up a complex process for any future president wishing to pull out.
The EU's 28 countries are expected to take up to about a year and a half, according to Maros Sefcovic, who will be signing on behalf of the EU as vice president.