"It's a consensus that meets numerous U.S.'s biggest objectives", said the official.
Greenpeace said that "the necessity of the United States being part of the effort to fight climate change can not be denied, but this is a demonstration that the U.S. is still the odd one out".
The "coalition" against the United States on climate change was beginning to fray, a senior White House official said, adding that several countries, including Turkey, Russia and Saudi Arabia, had balked at signing the document before finally backing it.
In addition, the declaration also touched on the 2016 Paris agreement on climate change, reiterating the G20 intent to continue "to tackle climate change, while promoting sustainable development and economic growth".
French President Emmanuel Macron, President Donald Trump and Japanese President Shizno Abe gather with other world leaders for the family photo on the opening day of G20 Summit on November 30, 2018 in Buenos Aires, Argentina.
While a statement is not legally enforceable, the Europeans see it as proof the G20 is still relevant and multilateralism still works.
He said: "We have agreed on a statement that reflects the necessity of revitalising trade, of revitalising the WTO". The European Union is also pushing for reform at the WTO. "That is why it's so important to come here and to express to political leaders how important it is for everybody to understand that this is a make it or break it moment in relation to guaranteeing that the Paris Agreement is implemented".
"We will send a clear signal - in any case, most of us" - for the success of global climate talks starting in Poland on Sunday, Ms Merkel added.
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Germany and France have sought to mediate between Russian Federation and Ukraine, and spokesman Steffen Seibert said Ms Merkel and Mr Putin agreed the four countries should hold further talks at the "adviser level".
Other hotspots such as Ukraine also flared up at the two-day summit, although Saudi Arabia's Crown Prince Mohammed bin Salman received an effusive welcome from Putin, showing the de facto ruler still has friends despite the killing of a dissident Saudi journalist.
May said she spoke to the crown prince about the importance of "a full, credible, transparent investigation that identifies those who are involved and that ensures that those involved are held to account". Mr Erdogan called Mr bin Salman's response - that the crime had not been proven - "unbelievable" and complained that Saudi authorities have been unco-operative.
Saudi Arabia has denied that bin Salman played a role, but US intelligence agencies concluded he ordered the killing.
Saturday will also see a highly anticipated meeting between U.S. President Donald Trump and Chinese President Xi Jinping, whose nations have been embroiled in an escalating trade war with new U.S. tariffs on China goods set to take effect a month from now.
But for financial markets, the weekend's main course comes after the summit when Trump is due to sit down to dinner with Chinese President Xi Jinping in Buenos Aires.
Argentinian President Mauricio Macri said in his closing remarks that the participating nations overcame "a number of challenges" to reach the communiqué.
"Leaders buried their differences in obscure language and dropped language to fight protectionism, which had been included in every G20 communique since the leaders' first summit. This is already something".