The Paris Climate Change Agreement achieved the first step required for it to enter into force on 21 September after 31 governments submitted their instruments of ratification, acceptance, approval or accession. The second step – ratification by countries representing a total of 55% of global emissions – is expected to be taken later this year. Some 60 countries representing 47.5% of global greenhouse gas emissions have now joined the agreement and another 14, representing 12.58% of emissions, have committed to join in 2016, "virtually assuring" that it will enter into force this year, the UN said.

The agreement was adopted by parties to the UN Framework Convention on Climate Change (UNFCCC) last December in Paris and signed by many parties early this year. Its main aim is to keep global temperature increases this century well below 2 degrees Celsius, and drive efforts to limit temperature increases to below 1.5 degrees Celsius, which UNFCCC says is a "significantly safer" defence against the worst impacts of climate change.

China and the USA, two of the world's largest carbon emitters, joined the agreement in September, which the UN said provided "considerable impetus" for other countries to complete their domestic ratification or approvals process.

"This momentum is remarkable," United Nations Secretary General Ban Ki-moon said. "It can sometimes take years or even decades for a treaty to enter into force. It is just nine months since the Paris climate conference. This is testament to the urgency of the crisis we all face." He called on world leaders to step up their domestic efforts to join the agreement this year. "What once seemed impossible is now inevitable," he said.

Entry into force will transform the climate action plans (Intended Nationally Determined Contributions), submitted by nations in the run up to the Paris conference into Nationally Determined Contributions. Governments will also be obligated to take action to achieve the two temperature limits enshrined in the agreement.