The ratification by the two countries, which emit the largest amount of greenhouse gas, marks an important step forward to put the agreement into force by the end of 2016, earlier than scheduled.
According to President Obama, climate change is an issue, more important than any challenges in this century, and the fight against climate change is not confined to an individual country.
The Paris deal is the sole and best opportunity to protect our planet.
President Xi expressed his hope that two countries’ decision will press more countries to take action, saying coping with climate change relates to the future of a country’s citizens and of humankind.
He pledged to seriously implement the agreement.
Statistics show China’s greenhouse gas emission accounts for 20% of the world, followed by the US with 15%.
Before China and the US, more than 20 countries, whose emission account for only 1.08% of the world, had ratified the Paris deal. The Paris agreement needs the approval of 55 countries to take effect.
With Beijing and Washington ratifying, UN chief Ban Ki-moon voiced his optimism that the agreement may begin take effect by the end of this year.
Before the G20 summit which took place from September 4 and 5 in China, 130 major investors sent an open letter to the summit, demanding concrete measures to shift to a green economy.
They said the primary task is to define carbon tax based on which financial resources will be mobilized.
According a study published on the Nature Climate Change journal in April, if the earth becomes 2.5 degrees Celsius warmer, bonds worth US$2.5 trillion are under threat.
Developing countries have to allocate higher budget for the climate change adaptation which cost from US$140 billion to US$300 billion per year until 2030, 4-5 times higher than predicted.
The Paris agreement was formally ratified by representatives from 195 countries in December 2015 in France. The deal, an important international document, is legally binding in greenhouse gas emission control.