NEW YORK -- United States Secretary of State John Kerry joined other world leaders Friday in New York for the official signing of the Paris climate agreement.

The signing ceremony formalized the agreement member countries reached in Paris last December as part of the United Nations Framework Convention on Climate Change, or UNFCCC. The deal committed world leaders to taking national actions in their countries to reduce emissions by 2020, toward the collective goal of limiting global temperature rise to "well below" 2 degrees Celsius .

Representatives from about 170 countries were expected to participate in the signing ceremony, according to the UNFCCC. Kerry, who came to the stage carrying his toddler granddaughter, signed on behalf of the United States, as President Barack Obama is out of the country.

"When enough people come out and make their voices heard, when they turn their policy into a voting issue, when they work together toward the same real goal, then measurable change is possible," Kerry said in his speech at the United Nations. "Today, as we think of the hard work ahead, I am reminded of Nelson Mandela's very simple words: 'It always seems impossible until it is done.' While it isn't done yet, today we are on the march."