Update: India, responsible for 4.1% of global emissions, has announced it will ratify the Paris Agreement in October.

"India will ratify the decision on October 2, the birth anniversary of Mahatma Gandhi," said Prime Minister Narendra Modi.

The biggest polluter in the world has just done something jaw-dropping. On the eve of its hosting of the G20 summit, China announced it had ratified the Paris Agreement on Climate Change.

During the same summit, the United States – the world’s second-largest polluter – also said that it had ratified the agreement.

Between them, the two countries represent almost 40% of global carbon emissions (37.98%). This development means that the Paris Agreement is one giant step closer to coming into effect.

What was the Paris Agreement?

Hammered out last year after two weeks of intense discussion by more than 190 countries, the agreement needs to be signed by 55 nations before coming into effect.

This interactive map shows the progress being made.

To date, the agreement has been signed by 180 parties and ratified or otherwise joined by 26 parties, representing 38% of global emissions. For the climate agreement to come into force, 39 more countries must sign up. Together all 55 must represent at least 55% of global emissions.

The US and China hope that their action will spur others to help make the agreement a reality.

Who hasn’t signed yet?

All eyes are now on the remaining seven top global polluters. The European Union is the third-largest polluter, producing 12.10% of global emissions.

Although the agreement was reached in December 2012, countries have to go through the process of adopting, signing and joining before it can come into full force. In most cases, a country then has to gain approval from its domestic government in order to proceed. This is the final stage of the process – the ratification – which the US and China have just completed.

The EU signed the agreement earlier this year, on 22 April, but has yet to ratify it. Its situation is a little more complicated, given that it represents 28 states. However, the European Council has put forward the suggestion that it could ratify the agreement on its members’ behalf, thereby speeding up the process.

“Right now we are developing the laws which will allow us to deliver our ambitious target for 2030. We expect the challenge of climate change to be dealt with in all seriousness by the G20 partners. In the meantime, the ratification process is underway in the EU and will be completed as soon as possible,” said Donald Tusk, President of the European Council at the opening of the G20 summit.

Russia, the fourth-largest polluter, representing 7.53% of global emissions, also signed the agreement in April, but has yet to ratify it.

“We (Russia) have significantly reduced greenhouse gas emissions. At the same time we have managed to double our GDP. We have demonstrated that we can ensure economic development and take care of our environment at the same time,” declared Vladimir Putin at the December meeting in Paris.

India is the fifth-largest polluter, with 4.1% of emissions. It signed the agreement in April, and said in June that it had started the domestic process to ratify it and that it intended to sign the agreement by the end of this year.

Of the remaining six largest polluters – Japan (3.79%), Brazil (2.48%), Canada (1.95%), South Korea (1.85%) and Indonesia (1.49%) – none has ratified the agreement, although all signed in April.

Japan, Brazil and Canada have all publicly said that they intend to by the end of the year.

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