China and United States, the world’s two largest emitters of greenhouse gases, jointly ratified on Saturday the Paris Agreement on Climate Change. This endorsement, by the two largest global economies, significantly advances the potential for rapid entry into force of the deal that would allow the baton to pass from commitments on paper to actions on the ground.

China’s top legislative body ratified the agreement on Saturday morning, hours before Chinese President Xi Jinping met with his US counterpart Barack Obama, on the sidelines of G20 summit taking place in Hangzhou, to make their joint announcement.

Cooperation between the United States China on climate change, once quite unimaginable, now stands as one of the brighter spots in their vacillating relationship. With the US now joining China in announcing ratification of the Agreement, pressure will mount on other G20 nations to move faster with their pledge to phase out subsidies to fossil fuels. But even if enough other players step forward to make the Paris deal law, huge challenges lie ahead.

As of 1 September 2016, the 24 parties that had ratified the agreement accounted for just 1.08 percent of emissions. With China, responsible for 20.09 percent of global greenhouse gas (GHG) emissions, and the United States, accounting for 17.89 percent, joining the tally has now jumped to 39.06 percent. With 32 more countries expressing their intend to ratify the Agreement before the end of 2016, the total could reach 59.88 percent, which would be sufficient to ensure the Paris Agreement enters into force by the end of the year.

However, analysts warn that the target of keeping temperature rises below 2C is already in danger of being breached. For 14 consecutive months meteorologists have recorded the hottest month on record, and the UK's Met Office has forecast that 2016 is likely to hit temperatures 1.1C above pre-industrial levels. Average temperatures worldwide are likely to increase more in the coming years as the effect of previous carbon emissions makes itself felt.

In December 2015, world leaders attending the United Nations in France, agreed on the landmark Paris Agreement that calls for keeping global temperatures below 2 degrees Centigrade compared to pre-industrial levels and pursuing efforts to limit it to 1.5°C. Other targets in the agreement include reaching zero-net greenhouse gas emissions as soon as possible and achieving a balance between sources and sinks of greenhouse gases in the second half of this century. It also calls for reviewing the progress in climate commitments every five years and providing US$100 billion a year in climate finance for developing countries by 2020, with a commitment to further finance in the future.

The agreement comes into force only after at least 55 nations representing 55 percent of total greenhouse gas emissions join by adopting it through ratification, acceptance, approval or accession by their own legal systems. Once the deal comes into force, countries that have ratified it have to wait for a minimum of three years before they exit.