China and the US – responsible for around 40 per cent of the world’s carbon emissions – on Saturday jointly ratified the Paris climate change deal that aims to significantly reduce global emissions, giving hopes that the landmark accord may come into effect by the end of this year.

Chinese President Xi Jinping and US President Barack Obama gave documents to UN Secretary-General Ban Ki-moon here entering their nations into global climate change pact.

Their approval to the agreement came a day ahead of the key summit of G20 nations in Hangzhou, where the leaders of the world’s 20 strong economies will meet.

China and the US together are responsible for around 40 per cent of the world’s emissions so their ratification of the international legal document is viewed crucial.

In a speech at a ceremony in the eastern Chinese city of Hangzhou, Obama said the Paris deal was the "single best chance that have to deal with a problem that could end up transforming this planet".

"We are moving the world significantly towards the goal we have set," he said, adding that history would show that the Paris deal would "ultimately prove to be a turning point".

Earlier on Saturday, China’s parliament ratified the agreement, with President Xi saying his country was "solemnly" committed to the deal.

"We need to take an innovative approach to climate change," he said in Hangzhou.

Xi said he hoped other countries would follow suit and advance new technologies to help them meet their targets.

"Depositing the documents together, China and the US have displayed their ambition and determination to jointly tackle a global challenge," Xi said.

The Chinese President said developed countries should honour their commitments and provide financial and technological support to developing countries and enhance their capability in climate actions.

"China, a responsible developing country and an active player in global climate governance, will implement its development concepts of innovative, coordinated, green, open and shared growth, fully advance energy conservation, emission reduction and low-carbon development, and embrace the new era of ecological civilisation," he said.

The Paris Agreement is the third attempt to address the issue of climate change, after the 1992 UN Framework Convention on Climate Change and the 1997 Kyoto Protocol.

The accord, which sets ambitious goals for capping global warming and funnelling trillions of dollars to poor countries, will come into effect 30 days after at least 55 countries, accounting for 55 per cent of global greenhouse gas emissions, have ratified it.

The Paris accord (COP21) aims to reverse temperature increase, mainly caused by carbon emissions. It sets a target to hold the global average rise in temperature below 2 degrees Celsius above pre-industrial levels, and preferably below 1.5 degrees.

It is a major milestone, especially after the failed climate summit in Copenhagen, Denmark, in 2009 and disputes among countries on their responsibilities.