With the ink barely dry, Obama expressed optimism that the regulatory steps G-20 leaders committed to take this afternoon would be considered a "turning point" in the pursuit of a global economic recovery.
"It was historic because of the size and the scope of the challenges that we face and because of the timeliness and magnitude of our response," Obama said.
But when asked during his post-G-20 press conference whether he could say with confidence that the steps taken by the industrialized nations today would prevent a further global economic slide, Obama took a wait-and-see approach.
"In life, there are no guarantees, and in economics, there are no guarantees," the president said. " I have no doubt, though, that the steps that have been taken are critical to preventing us sliding into a depression. ... I think the steps in the communique were necessary. Whether they're sufficient, we've got to wait and see."
He said the steps agreed upon by the world leaders, who together control 85 percent of the world's wealth, were critical but "not a panacea."
Whether this summit enacted what will be solutions to the global recession won't be known for months.
Read ABC News' George Stephanopoulos' analysis of President Obama's G-20 news conference.
Obama's remarks came as the leaders of the world's wealthy nations agreed today to inject $1 trillion into the global economy in an effort to pull it out of the spreading recession.
Brown called the investment the "largest macroeconomic stimulus the world has ever seen."
"We are undertaking an unprecedented and concerted fiscal expansion," a communique from the G-20 group said.
Obama said that world leaders have "learned the lessons of history" and warned against retreating behind borders.
"History tells us that turning inward can help turn a downturn into a depression," he said. "And this cooperation between the world's leading economies signals our support for open markets, as does our multilateral commitment to trade finance that will grow our exports and create new jobs."
Brown, who's been the president's wingman throughout the summit, suggested that the days of U.S. primacy are long gone, pointing to Thursday's summit as an archetype for future global negotiations.
"The old Washington consensus is over. Today, we have reached a new consensus that we take global action together to deal with the problems we face," he said.
While Obama upheld America's role as a leader on the world stage, he noted that there are now more players at the negotiating table and nations like Japan, China and India now play critical roles in the global economy.
"If it's just Roosevelt and Churchill sitting in a room with a brandy, you know, that's an easier negotiation. But that's not the world we live in. And it shouldn't be the world that we live in," he said.
The communique predicted the stimulus plan "will save or create millions of jobs which would otherwise have been destroyed, and that will, by the end of next year, amount to $5 trillion, raise output by 4 percent, and accelerate the transition to a green economy."