As many as 171 countries inked the historic Paris climate deal at the UN headquarters in New York on Friday.
The climate pact, which has been negotiated over decades, elicits a pledge from countries to limit global rise in temperatures to below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.
The UN said as many as 175 countries have signed the agreement so far and 15 of them have ratified the deal. However, the deal will not come into force before dozens of other countries, especially the larger ones with higher carbon emissions, ratify it.
The 1997 Kyoto Protocol, which came into force in 2005, had required only developed countries to cut greenhouse gas emissions.
The key countries are China and the US, which together account for 38 percent of global emissions.
China has said it will finalise domestic procedures for the ratification of the Paris Agreement before the G20 summit in China in September.
"China will finalise domestic legal procedures on its accession before the G20 Hangzhou summit in September this year," Vice Premier Zhang Gaoli said.
US President Barack Obama has committed to push through the ratification process before he exits office in January.
However, a lot depends on how fast Obama moves on this. There is some concern over the ratification process in the US as Republican presidential candidate Donald Trump has said he will reverse course on Paris Agreement if he comes to power.
"What happens in the US will have a definite bearing on how the world takes all these ideas and commitments and pledges in effect. So people are eagerly awaiting what happens in the US," Indian environment minister Prakash Javadekar told BBC.
The ratification process in Europe, which accounts for more than 10 percent of global emissions, will be a long-drawn process as each of the 28 members has to ratify the pact.
UN Secretary-General Ban Ki-moon said the Paris agreement on climate will shape the lives of all future generations in a profound way.
"We are in a race against time. I urge all countries to join the agreement at the national level. Today we are signing a new covenant for the future," he said.
UN climate chief Christiana Figueres said most countries that signed the deal on Friday need to go back home and go to ratification procedures.
"After 21 years of debates and conferences it's time to declare no more talks, no more 10-year studies, no more allowing the fossil fuel companies to manipulate and dictate the science and the policies that affect our future. This is the body that can do what is needed," said Hollywood actor and climate change campaigner Leonardo DiCaprio.
Singapore signs deal
Foreign Affairs Minister Vivian Balakrishnan signed the treaty on behalf of Singapore. He said Singapore's carbon footprint is rather small at 123rd spot in a list of 142 countries worldwide, but promised the country will "continue to do more".
"Within the geographical constraints we face, we will pursue renewable energy in the form of increased solar PV (photovoltaic) deployment. This will supplement our substantial energy efficiency efforts and other mitigation measures to lower our Emissions Intensity by 36 per cent from 2005 levels, and to stabilise our emissions around 2030," Balakrishnan said.
