The U.S. and China have announced they will formally sign the Paris climate agreement as U.S. President Barack Obama met with Chinese President Xi Jinping and United Nations (U.N.) Secretary General Ban Ki-moon in Hangzhou on Saturday on the eve of the Group of 20 (G20) summit.\u0022Just as I believe the Paris agreement will ultimately prove to be a turning point for our planet, I believe that history will judge today\u0026#039;s efforts as pivotal,\u0022 Obama said.Earlier in the day, Xi had separately vowed to \u0022unwaveringly pursue sustainable development\u0022 as part of China\u0026#039;s climate plan.The U.S. and China are the world\u0026#039;s biggest polluters, together comprising 40 percent of global greenhouse gas emissions. Their formal ratification of the agreement could provide the necessary push to implement the Paris accord by the end of the year.Climate groups received the news with the hope that the treaty\u0026#039;s signatories will actually keep their promises. The climate treaty calls for keeping global temperatures from rising 1.5°C, the scientifically agreed-upon threshold for irreversible planetary changes.\u0022The Paris agreement could be the next nail in the coffin of the fossil fuel industry if governments actually follow through on their commitments,\u0022 said May Boeve, executive director of 350.org. \u0022The only way to reach the 1.5° or 2°C targets is by keeping coal, oil, and gas in the ground.\u0022The Guardian sums up:If the Paris agreement comes into force this year as hoped, it means the nearly 200 governments party to it will become obliged to meet emissions-cutting pledges made before the deal last December. For example, the E.U. has a \u0022national determined contribution\u0022 of cutting emissions 40 percent by 2030 on 1990 levels, and the U.S. by up to 28 percent by 2025 compared with 2005.But as Boeve also noted, even if governments walk the walk on curbing emissions, there remains a \u0022dangerous gap\u0022 between those actions and \u0022the real ambition we need to avert the worst impacts of climate change.\u0022\u0022As a movement, we will continue to push governments to go well beyond their current targets and accelerate the transition to 100 percent renewable energy,\u0022 she said.Still, \u0022While it\u0026#039;s not everything we hoped for, the implementation of the Paris agreement will radically remake the energy sector,\u0022 Boeve added. \u0022The U.S.-China announcement serves as another warning bell for investors to take climate risk seriously and divest from fossil fuel companies.\u0022Greenpeace East Asia\u0026#039;s senior climate policy adviser Li Shuo said the pressure was on for Xi to \u0022move from agreement to action.\u0022\u0022Political ambition must keep up with rising sea levels faced by vulnerable communities around the world,\u0022 he added.