As many as 170 countries are expected to sign the Paris Agreement on climate change Friday as the landmark deal takes a key step toward entering into force years ahead of schedule. As many as 170 countries are expected to sign the Paris Agreement on climate change Friday as the landmark deal takes a key step toward entering into force years ahead of schedule. U.S. Secretary of State John Kerry joins dozens of world leaders for a signing ceremony that is expected to 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 now 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 Paris Agreement through their domestic procedures. The United Nations says at least 13 countries are expected to do that Friday by depositing their instruments of ratification.

Artwork entitled 'Earth Crisis' by American artist Shepard Fairey is displayed on the Eiffel Tower illuminated in colour, as part of the organisation of the Conference on Climate Change COP21 on Nov. 22, 2015 in Paris. (Photo: Chesnot/Getty Images) The agreement will enter into force once 55 countries representing at least 55 per cent of global emissions have formally joined it. The United States and China, which together account for nearly 40 per cent of global emissions, have said they intend to join this year. "We definitely want to be in the first wave of ratifying countries," Maros Sefcovic, the energy chief for another top emitter, the 28-nation European Union, told reporters Thursday. "We definitely want to be in the first wave of ratifying countries." Countries that had not yet indicated they would sign the agreement Friday include some of the world's largest oil producers, including Saudi Arabia, Iraq, Nigeria and Kazakhstan, the World Resources Institute said Thursday. The Paris Agreement, the world's response to hotter temperatures, rising seas and other impacts of climate change, was reached in December as a major breakthrough in U.N. climate negotiations, which for years were slowed by disputes between rich and poor countries over who should do what. Under the agreement, countries set their own targets for reducing emissions of carbon dioxide and other greenhouse gases. The targets are not legally binding, but countries must update them every five years.