China and the US, the world’s two largest carbon polluters, have both ratified the Paris climate change agreement in a big boost to efforts to bring the UN accord into force, the Financial Times reports. “History will judge today’s effort as pivotal,” said US president, Barack Obama, on Saturday as the two countries formally submitted their ratification plans to the UN. The US and China made their announcement as leaders gather in the Chinese city of Hangzhou for the G20 summit, a move welcomed by climate campaigners around the world and some investors. The pact adopted by more than 190 countries in Paris in December is the culmination of more than 20 years of effort to cut global greenhouse gas emissions and many nations are eager for it to take effect.