"The fact that the G20 is taking place in South America for the first time is nearly beside the point", Mr Shifter said.
In remarks opening Saturday's session, Argentine President Mauricio Macri said his country is committed to the Paris accord, protecting marine areas and lowering emissions, calling sustainable development "the north star of all our economic, social and environmental goals".
Thousands of people on Friday demonstrated against a G20 summit taking place in Buenos Aires, accusing the group of industrialized nations of imperialism and exploitation.
After the meeting, the PMO tweeted that the two leaders held productive discussions. When a meeting does happen, Putin said there will be no preconditions.
Saudi Arabia has denied that the prince played a role, but U.S. intelligence agencies concluded he ordered the killing. She had to take commercial flights to Argentina.
It is to be bin Salman's first significant appearance overseas since the killing.
Trump was also scheduled to speak with German Chancellor Angela Merkel and Turkish President Recep Tayyip Erdogan. One French source said European leaders were trying to forge a separate statement on climate change excluding the US.
Although the new pact inherits key features from the old one, Trump has declared it a victory for the U.S. workers he claims were cheated by NAFTA and on Friday called it the most "modern and balanced agreement in history".
With a major United Nations meeting on climate change starting in Poland straight after the G20, United Nations chief Antonio Guterres said in Buenos Aires that "this is a make-it-or-break-it moment".
The G20 had a rocky start following the meeting between Macri and Trump on Friday morning.
The G20 summit is the biggest global gathering in Argentina's history, and the protest underlined security concerns after recent football violence forced the relocation of a showpiece final to Spain.
"We discussed situation in Manbij, Idlib and terrorist groups in northern Syria with U.S. President Donald Trump", Erdoğan said later on Saturday.
Shannon O'Neil, an expert on global trade at the Council on Foreign Relations, said she believes it "very likely" that the tariffs will take effect in January.
"I just said we brought it up", she said. "It used to be Mexico and Nafta, and now it's going to be China".
However, Trump made clear that he also wants to follow up on his historic June summit in Singapore as he tries to persuade the reclusive regime to give up its nuclear weapons.
He indicated that the global challenges require global solutions, and at the same time said consensus "cannot be reached overnight" and they are processes "with its ups and downs" that continue beyond the summit. "I think I understood you better in your language than I did on this, but that's OK", Trump told Macri and then dropped his earpiece on the floor.
The pact must still be approved by politicians in all three countries.
"I think the worst of it is that the conflict between China and the U.S.is again showing the limits of multilateral institutions, in particular the World Trade Organization", Roberto Bouzas, an worldwide relations and economics professor at the Universidad de San Andres, tells VOA.
Macron and British Prime Minister Theresa May both said they were raising the killing of Khashoggi during meetings with the 33-year-old prince. The two have increasingly clashed in recent weeks on everything from Mr Trump's nationalism to wine tariffs.
Mr Trump said he is hopeful for agreement at "some point".
The other key attendees on the American side, according to the White House, will be Secretary of State Mike Pompeo, Treasury Secretary Steven Munchin, White House Chief of Staff John Kelly, U.S. Trade Representative Robert Lighthizer, national security adviser John Bolton, Trump son-in-law and senior adviser Jared Kushner, and Larry Kudlow, assistant to the president for economic policy.
Other European leaders at the summit are facing domestic struggles of their own.
Amid the Ukraine crisis, European Union president Donald Tusk said he was "sure" that the EU would roll over its sanctions on Russian Federation next month.