Up to 170 countries are expected to sign the Paris Agreement on climate change Friday as the landmark deal moves closer to entering into force years ahead of schedule.

Secretary of State John Kerry is joining dozens of world leaders for a U.N. ceremony that should set a record for international diplomacy: Never have so many countries signed an agreement on the first available day.

States that don't sign Friday have a year to do so.

Many expect the climate agreement to enter into force long before the original deadline of 2020. Some say it could happen this year.

After signing, countries must formally approve the agreement through their domestic procedures. The United Nations says at least 13 countries could take that step Friday by depositing their instruments of ratification.