It began as a movement of pacifists chaining themselves to fences outside nuclear power plants. Five decades later, the effort to close German nuclear power plants will end with echoes of the Cold War era in which it began, as Russia’s war in Ukraine is a reminder of both the risks and promise of nuclear energy.

Germany’s three remaining reactors will be shut down by Saturday — ending nuclear power generation in Europe’s largest economy. But it comes as the continent grapples with questions over whether it can secure enough energy to drive its economies and keep homes warm while also reaching ambitious climate targets.

Germany’s move makes it an outlier in much of the industrialized world. Britain, Finland and France are doubling down on nuclear energy as a source of reliable electricity and extremely low carbon emissions. Last year, Poland signed with Westinghouse Electric to build its first nuclear power plant, some 200 miles east of the German border.

In the United States, the Biden administration is backing technology to build a new generation of smaller nuclear reactors as a tool of “mass decarbonization.”

Some polls suggest that even Germans, once largely behind the shutdown in their country, are having doubts: In a survey commissioned by Germany’s largest daily, Bild, 52 percent opposed ending nuclear power, given that the country is pivoting from its dependence on fossil fuels from Russia.

Robert Habeck, the economy minister and a member of the Greens party, insists that Germany can manage the nuclear exit. The country’s natural gas storage tanks, he pointed out, are more than half full — a significant cushion with the heating season almost over. And Germany has rapidly built liquefied natural gas terminals that allow it to import gas from cargo ships instead of through the Russian pipelines that once provided some 55 percent of Germany’s supply.

“Energy supply security in Germany has been ensured during this difficult winter and will continue to be ensured,” Mr. Habeck said in an interview with the Funke Media Group. In contrast, new European nuclear plants have been a “fiasco,” he argued, plagued by soaring costs, construction delays and maintenance issues. “Our energy system will be structured differently: We will have 80 percent renewable energies by 2030.”

Nuclear power has been a longstanding fault line of German politics. Peace activists appalled by the Cold War fought atomic energy since the 1970s, with some becoming founding members of the Greens, which is now in Germany’s three-party coalition government. The antinuclear movement grew after the 1986 Chernobyl disaster created a cloud of nuclear fallout that reached West Germany, leaving scarring memories among that generation.

By 2000, a left-leaning government had approved a plan to shut down German nuclear power, only to have a conservative government led by Angela Merkel roll it back.

Yet the Fukushima nuclear disaster in Japan in 2011 caused German sentiments to shift strongly against atomic energy once more, and Ms. Merkel abruptly reversed course. Her government passed a law to phase out Germany’s 17 nuclear reactors by the end of 2022.

The nuclear debate took another twist last year when Germany faced its first winter without fuel from Russia. As officials urged businesses and consumers to reduce energy consumption or face rationing, Chancellor Olaf Scholz extended the lives of the last three plants until April 15 to ensure sufficient energy at a reasonable price until spring.

But with no end in sight to the war in Ukraine, business leaders warn that this is no time to cut off a source of relatively cheap electricity.

“We must continue to do everything possible to expand energy supply and in no way restrict it further,” Peter Adrian, head of the German Chambers of Commerce and Industry, said in a statement, warning that power instability could endanger the country’s position as an industrial powerhouse.

On Thursday, two dozen scientists and Nobel Prize laureates from across the globe sent a letter to Mr. Scholz urging him to reverse course, citing nuclear power as a valuable alternative to power plants spewing greenhouse gases.

“Germany’s electric grid remains among the most carbon-intensive in Europe,” the organizers of the letter, an alliance called RePlanet, said in a statement.

The International Energy Agency said last year that nuclear power could be crucial to helping reduce carbon emissions in line with the goals of the Paris climate accord. It stressed that nuclear could also play a role in developing carbon-free synthetic fuels known as green hydrogen.

But climate and energy experts predict that Germany’s nuclear shutdown will create only a slight, temporary increase in its carbon emissions — counterbalanced in the next few years by increases in solar and wind power.

Andrzej Ancygier, an expert at the think tank Climate Analytics in Berlin, rejects the argument that nuclear power is more reliable than wind or solar. He pointed to last summer’s droughts and high temperatures, which forced several European countries to shut down reactors when the rivers used to cool the plants dropped too low, or their water became too warm.

“We’re getting to a place where the planet is becoming warmer, more dangerous and more unstable. We could end up in a bad place,” he said. “Safety is an issue here. It’s something we forgot, but we shouldn’t have.”

Germany’s environmental minister, Steffi Lemke, argued that the war in Ukraine had added to the riskiness of nuclear power.

“We are faced with a situation where nuclear power plants in Ukraine are being shelled because of Russia’s war of aggression and have become the target of military conflicts,” she told the German broadcaster Deutschlandfunk. “Nuclear power plants were never designed for such a situation.”

The three German reactors scheduled for shutdown are safe and could continue to provide power at relatively low cost for many years to come, making the decision to switch them off an expensive one, said Georg Zachmann, a climate and energy expert at the Bruegel think tank in Brussels. At the same time, he said, plants under construction in Britain, Finland and France are running over budget, making the energy they could provide up to three times as expensive.

“I would not argue that only the Germans are crazy,” Mr. Zachmann said. “Shutting down existing nuclear power is expensive, and building new is expensive.”