A madness is taking hold. In the same week as Arctic ice cover is recorded at its lowest ever extent, two major countries decide to reduce or eliminate their use of the only proven source of low-carbon power that can be deployed at sufficient scale to tackle our climate crisis. Japan plans to phase out nuclear entirely by 2030, its prime minister announced today. The French president has just revealed a plan to dramatically reduce the country's reliance on nuclear, which currently gives France some of the cleanest electricity in the world.

Let me be very clear. Without nuclear, the battle against global warming is as good as lost. Even many greens now admit this in private moments. We are already witnessing the first signs of the collapse in the biosphere this entails – with the Arctic in full-scale meltdown, more solar radiation is being captured by the dark ocean surface, and the weather systems of the entire northern hemisphere are being thrown into chaos. With nuclear, there is a chance that global warming this century can be limited to 2C; without nuclear, I would guess we are heading for 4C or above. That will devastate ecosystems and societies worldwide on a scale which is unimaginable.

Given the trauma the Japanese people have suffered since the earthquake and tsunami of 11 March 2011, it is understandable that major questions are asked of domestic politicians. But we must never forget that Fukushima has killed no one. More people in Japan recently died from an E coli outbreak due to eating contaminated pickles. Scientists also agree there will never be an observable cancer increase in the Japanese population attributable to Fukushima.

But in response to the nuclear shutdown, oil and gas imports to Japan have doubled, and carbon dioxide emissions soared by more than 60m tonnes. Any environmentalist who celebrates this outcome is not worthy of the name.

Japan is already backing away from its own climate change targets. As a participant in the UN climate negotiations last year, I watched this happen. Under the 2009 Copenhagen accord, Japan pledged to reduce CO 2 emissions by 25% by 2020. The plan was to increase nuclear to half of national electricity in order to facilitate the carbon cuts, supported by an increase in renewables to 20% by 2030. To reach the same targets without nuclear is impossible; wind and solar combined meet barely 1% of electricity production today in Japan, and there is no way they can be deployed at sufficient scale to meet the gap. So the climate targets will be dropped, as Japan re-carbonises its economy.

It is nothing short of insane that politicians around the world, under pressure from populations subjected to decades of anti-nuclear fearmongering by people who call themselves greens, are raising our collective risk of catastrophic climate change in order to eliminate the safest power source ever invented.

More people die each day from coal pollution than have been killed by nuclear power in 50 years of operation, and that is even before factoring in the impact on global warming. That such populist irrationality should guide public policy in so many countries – and on such an important issue as energy – is nothing short of a disaster.

All is not yet lost. 2030 is a long way away, and as Japan watches its heavy industry shut down and relocate offshore due to rising energy costs and supply shortages, there may be a rethink. France may decide to keep its nuclear stations as it watches Germany's much vaunted dash for solar dissolve in a cloud of coal smoke. But ultimately energy policy must be responsive to public opinion, and as long as people across the world get it so wrong on nuclear risk and continue to ignore the real and rising risks of climate change, the planet is in very serious trouble.