Four prominent climate scientists gave a press conference at the sidelines of the Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC) late last year in Paris. To the surprise of casual observers, the discussion was a call for nuclear power to be given a fair hearing in the fight against climate change.

First at the bat was Dr Ken Caldeira, who was arrested in 1981 for protesting the Shoreham Nuclear Power Plant on Long Island, New York (the plant was eventually decommissioned). Then a freelance software developer, Caldeira was a key figure in the anti-nuclear weapons and power movement and was involved in the 500,000-strong protest in Central Park in June 1982.

Thirty-five years down the road, Caldeira sat with Dr Tom Wigley, Dr James Hansen and Dr Kerry Emanuel at the press conference organised by Energy for Humanity (energyforhumanity.org). Excerpts from the event were made available to the media globally.

At the meeting, the scientists urged policy-makers not to blindly exclude nuclear power in the fight to curb man-made emissions of greenhouse gases. Their reason: there is no other technology at present which can generate lots of electricity or heat needed by modern civilisation while emitting little carbon dioxide (CO2), one of the leading greenhouse gases (GHGs).

The nuclear option

Those following the reports from the UN scientific body, the Intergovernmental Panel on Climate Change (IPCC), would note that nuclear is now deemed in much more favourable light since the first report came out in 1990. The fifth report, released in 2014, held that nuclear power has the lowest CO2 output for each unit of electricity generated, except for wind energy from onshore wind farms. It cited studies that demonstrate that nuclear energy?s life-cycle emissions are comparable to sources like wind, solar photovoltaic (PV), geothermal, and hydropower. Compared to coal or natural gas-fired plants, nuclear is the hands-down winner.

When measured in terms of grammes of CO2 equivalent per kilowatt-hour of electricity generated, scientists can compare the carbon footprint of the various generation technologies. While some studies show nuclear to have a big carbon footprint of 100g CO2eq per kWh, average estimates put it at between 10g and 20g of CO2 per kWh, less than median estimates for PV (46g per kWh) and biomass (230g per kWh).

According to the International Energy Agency (IEA), nuclear power is the largest source of low-carbon electricity in the Organisation of Economic Cooperation and Development (OECD) countries (34 governments) and second at global level. It says limiting carbon emissions in electricity generation is an effective way to curb the build-up of GHGs in the atmosphere, given that this sector contributes more than 60% of all GHGs.

The four scientists are up against many others who insist that decarbonisation can be accomplished by hastening the use of renewables coupled with drastic improvements in energy efficiency. Under this proposition, nuclear energy is excluded as being unnecessary, if not downright dangerous. The scientists are firm in their conviction that we can prevent the worst effects of climate change by 2100 only by combining nuclear power with all major sustainable energy options.

Caldeira, now with the Carnegie Institution for Science and also a professor at Stanford University?s School of Earth, Energy and Environmental Sciences, is one of the lead authors of IPCC?s fifth report. At the press conference, he said he had previously over-estimated the contribution from renewables.

?Back then, I thought things like bio-energy, wind and solar could solve the problems, but then I came to see the magnitude of the problem was so great that we can?t afford to not use technologies that can do the job. There is only one technology that I know of that can provide the carbon-free power we need when the wind is not blowing or the sun is not shining, at the scale modern civilisation needs, and that is nuclear.?

Dr Kerry Emanuel, professor of atmospheric science at Massachusetts Institute of Technology, said they arrived at their conclusion after diligent research.

?That study has strongly led us to the conclusion that we are taking on unacceptable risks for future generations, and that is the reason we are here today (to speak on nuclear).

?Why are four scientists without a solid grounding in nuclear physics talking about nuclear energy? It is because we are scientists, and we can do the math. If we are truly sincere about solving the problem, we are going to have to ramp up nuclear power quickly. That is reality, that is not my ideology. The numbers don?t add up if we don?t put nuclear in the picture.?

None of the scientists are anti-renewables, even though they called for a realistic assessment of current renewables. ?We can ramp up solar, but then, we run head-long into the barriers dictated by intermittency (fluctuations in output caused by varying weather). We have to understand the limitations,? said Emanuel, who specialises in atmospheric convection and the mechanisms that combine to make hurricanes more destructive.

Fair hearing

Caldeira affirmed that their?s is not an either-or proposition. ?It is not choosing between solar, wind, or other renewables. I am in favour of anything that can preserve the environment. Let?s focus on the climate agenda, and it is about supplying energy in a way that does not destroy the environment.?

For Dr Tom Wigley of University of Adelaide, who has been involved in climate and carbon cycle modelling for many IPCC reports, the complexity of climate change calls for all options to be on the table. ?Because it is such a demanding, challenging problem, we cannot close the door to any type of technology. We have to give a fair and balanced assessment, eschewing ideologies and preconceptions to decide on what the energy strategy should be.?

Though CO2 levels in the atmosphere are now around 400ppm (parts per million), Dr James Hansen said it is still possible to get back to 350ppm (see 350.org) if abundant carbon-free electricity can be made available. The professor at the Department of Earth and Environmental Sciences at Columbia University and former head of NASA?s Goddard Institute for Space Studies, said powerhouses like China and India are well aware that their needs are not going to be met by renewables alone.

?There is no way they can power their steel mills on solar panels, and almost all the electricity is generated from coal. To lift people out of poverty, they need energy. If they don?t have alternatives, they would be burning coal. What the science says is that we should not be building new fossil fuel plants. Clearly, next generation nuclear power has tremendous potential to be a big part of the solution.?

The IEA has set the target of cutting energy-related CO2 emissions by more than half in 2050 (compared with 2009) and ensuring that they continue to fall thereafter. ?This scenario includes 18% of global electricity being supplied by nuclear energy by 2050, and to reach this target, global nuclear capacity would need to more than double,? said executive director Fatih Birol at the Energy for Tomorrow conference in Paris in December.

At the same event, World Nuclear Association director-general Agneta Rising said the sidelining of nuclear is a disservice to mankind.

?Nuclear generation could provide 25% of the world?s electricity with low-carbon generation by having 1,000GW (gigawatts) of new build by 2050,? she said. ?This silence on nuclear energy in discussions on climate change is misleading the public.?