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LONDON — This week, as Japan suspends work at Hokkaido 3, its last operating nuclear reactor, many alarmed by last year’s Fukushima crisis will breathe a sigh of relief.

But the shutdown renews concerns over whether green energy sources are capable of picking up the slack as Japan and other countries turn their backs on nuclear power. And if they are not, does this mean an end to hopes that renewable power will save the planet from catastrophe?

In Japan, where 54 nuclear reactors are now lying idle, perhaps never to be revived, the huge shortfall in energy supply is being met by increasing the burden on traditional gas, coal and oil-fired power stations, many of which were previously restricted to part-time service.

Japan isn’t the only country to turn its back on nuclear. In the wake of the Fukushima meltdown, Germany, Belgium and Switzerland all announced atomic shutdowns. Other countries, such as China and France, have drastically scaled back plans for constructing new power plants.

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It is a reaction that has provoked concern among some green energy campaigners, but also raised the divisive issue of whether the nuclear industry, with its track record of environmental disasters at Three Mile Island and Chernobyl, should be part of efforts to combat climate change.

Opinion has certainly strengthened against nuclear in recent months. A poll last November found that just 22 percent of people questioned worldwide agreed that nuclear power is relatively safe and that more nuclear power plants should be built.

The same poll also showed that 71 percent of people questioned in major energy-consuming countries such as the United States, Germany, France and the U.K. thought that renewable energy could replace coal and nuclear over the next two decades.

Some energy experts agree such an outcome is feasible, while others dismiss it entirely, according to Antony Froggatt, energy policy consultant and senior research fellow at London’s Chatham House think-tank.

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“It becomes partly an economic choice, partly an energy system choice and partly a societal choice in terms of some people would prefer to have a nuclear power station than a series of wind turbines,” he told GlobalPost.

The Intergovernmental Panel on Climate Change, for example, argues that close to 80 percent of the world’s energy supply could be met by renewables by 2050 — a scenario that sees both nuclear and fossil fuel use sidelined.

Another vision, presented by the International Energy Agency, sees nuclear as a crucial part of the solution because wind, solar, geothermal and hydroelectric power aren't yet developed enough to meet goals on reducing carbon dioxide emissions.

Earlier this year, the IEA’s chief economist, Fatih Birol, warned that with nuclear being squeezed out of the equation, heightened reliance on fossil fuels will mean the planet’s temperature will rise by far more than the two degrees Celsius (3.6 degrees Fahrenheit) that many see as manageable collateral damage.

Last week, IEA’s deputy executive director, Richard H. Jones, implored governments to act to avoid a doubling of CO2 emissions by 2050. This, he said, would lead to a temperature rise of at least 6 degrees celcius, with ecologically devastating consequences.

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“Such an outcome would confront future generations with significant economic, environmental and energy security hardships — a legacy that I know none of us wishes to leave behind,” he told an international meeting of energy ministers in London.

The IEA says governments are failing to sufficiently invest in or encourage energy-efficient technology or introduce carbon capture and storage techniques to reduce emissions. It says the economic crisis is partly to blame as subsidies and incentives have been cut amid austerity measures.

Economics frequently raises its head in the debate over nuclear, renewable and fossil fuels. Europe’s renewable energy companies have seen profits hit by cuts in government subsidies and competition from China — raising further doubts that emissions targets can be met.

Some opponents have criticized renewable energy as unreliable and inefficient, with the high cost and environmental impact of producing and installing equipment like solar panels or wind turbines far outweighing the benefits.

Then there are the bankruptcies that have blighted the once-booming solar and wind sector. Many companies operating on wafer-thin margins to stay afloat amid fierce competition have sunk in recent months as economizing governments tweak investments and subsidies.

Rupesh Madlani, a clean technology analyst at Barclays, said issues faced by manufacturers were a "market correction" after a surge in demand anticipated in 2008 failed to materialize. He said there could be more bankruptcies on the way.

"I believe we're a long way through a period of restructuring and we would expect to see a significant amount of consolidation to achieve a more stable equilibrium between supply and demand," he said.

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Politicians, meanwhile, have condemned emissions targets for wreaking havoc with their already burdened economies. Britain’s finance minister, George Osborne, recently said green initiatives were “putting our country out of business.”

There are, however, arguments on both sides of the nuclear debate that market forces, if deployed properly, will offer a solution.

Anti-nuclear campaigners, for instance, say that although there will be a short-term gain in fossil fuel consumption as countries like Germany take reactors offline, this will be offset as levies on pollution kick in, thus making renewable energy more economically attractive.

Meanwhile, pro-nuclear organizations such as the IEA say that if worldwide subsidies are removed from fossil fuels and prices reflect both the negative and positive impacts of consumption, this will create a level playing field in which renewables and nuclear can compete.

Germany, Froggatt said, makes for an interesting case study. Having already deployed solar panels capable of generating a “staggering” 7 gigawatts of energy, its renewable sources now generate more energy than its dying nuclear sector.

But with German reliance on traditional power stations forecast to create an extra 300 million tons of carbon dioxide between now and 2020 — more than the annual emissions of Italy and Spain combined — the country must rely on energy consumers to enact efficiencies if it is to hit emissions targets, yet another variable in the environmental equation.

If all this seems to suggest that no one really knows to what extent we will be able to rely on renewable at the expense of nuclear power and fossil fuels, that’s probably because so far no one actually does know, says Froggatt.

He added: “Many people have produced a scenario with a world running on 100 percent renewables, but you could come up with any percentage and there would be arguments for it.”