More than 165 world leaders are at the United Nations' headquarters to sign the Paris climate deal and get the ball rolling on plans to curb global warming.
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The signing, held on Earth Day, comes four months after the pact was agreed in principle at COP21 summit and marks the first step towards binding countries to the promises they made to cut greenhouse gas emissions.
"We are breaking records in this Chamber—and that is good news," U.N. Secretary-General Ban Ki-moon said in opening remarks Friday. "But records are also being broken outside; record global temperatures. Record ice loss. Record carbon levels in the atmosphere. We are in a race against time."
The U.N. expects some 60 heads of state at the signing ceremony. Brazilian President Dilma Rousseff, French President Francois Hollande and Canada's Justin Trudeau joined John Kerry, the U.S. secretary of state, for the event, the largest single-day signing of an international agreement.
Hollywood actor and environmental activist Leonardo di Caprio also addressed the audience, warning that "our planet will not be saved unless we leave fossil fuels in the ground where they belong."
"We can congratulate each other today," he said, "but it will mean absolutely nothing if you return to your countries and don't take action to implement the deal."
Actor Leonardo DiCaprio speaks at the U.N. headquarters in New York, April 22, 2016 | Reuters
The pact seeks to keep temperatures from rising any more than 2 degrees Celsius, sets individual emission targets for nations, asks countries to be transparent in their reports on emissions and requests that wealthier nations give financial support to poor nations to help them reduce their harmful gas usage.
Many states still need a parliamentary vote to formally approve the agreement. It will only enter into force when ratified by at least 55 nations representing 55 percent of man-made greenhouse gas emissions.
Although the target date for the agreement to begin is 2020, some experts predict the 55 percent threshold can be reached this year. The United Nations said 13 countries, mostly small island states, are set to formally ratify the agreement on Friday.