Sven Teske, Greenpeace's renewable energy director, said Germany was able to fill its energy gap left by idled nuclear plants with wind and solar power, though it has had to import some energy from nuclear-reliant neighbors.
"Switching to renewable is a matter of years, not decades," Teske said.
The International Panel on Climate Change, a scientific body set up by the UN and winner of a Nobel Peace Prize, says a global phase-out of nuclear power plants is feasible at moderate costs and without taking away from climate change efforts.
Artur Runge-Metzger, a European Union climate change official in Bangkok, said the issue is often seen in terms of "two kinds of evils."
"On the one hand you say we can't use nuclear energy because we might have nuclear disasters, but everybody at the table is also saying if we have climate change it is also going to lead to disaster," he said. "So we have to find a way forward."
Associated Press reporters Mari Yamaguchi in Tokyo and Juergen Baetz in Berlin contributed to this report.