John Holdren, President Obama’s science advisor, came to MIT last week to give a lecture on the role of nuclear power in addressing the climate and energy crises.

He described the daunting climate challenge the world faces. In order to stabilize the level of atmospheric carbon dioxide at 450 parts per million (ppm) we’ll have to level off carbon dioxide emissions by 2020 and cut them to half of 2000 levels by 2050.

The 450 ppm should keep global warming to 2°C by the end of this century, which gives us a decent shot at avoiding unmanageable climate change.

The question is how are we going to manage that. Global emissions leveled off in 2009 thanks to the recession, but China’s emissions grew by 9% that year and the past decade has seen a global annual average increase of 2.5%.

Fossil fuels drive 80% of the world’s energy system. This system represents a $15 trillion investment, and it will take 30 to 40 years to completely remake the system, said Holdren.

Achieving the 450 ppm goal means cutting CO2 emissions by 7 to 9 gigatons per year below the business-as-usual scenario, said Holdren. And that means we’re going to need contributions from many sectors and technologies, he said, alluding to the Stabilization Wedges strategy that calls for developing eight technologies that have the capacity to reduce CO2 emissions by one gigaton each.

We could achieve one of those gigatons by replacing coal-fired power plants with 700 1-gigawatt nuclear power plants, Holdren said. There are about 440 nuclear power plants in the world today, 104 of them in the US.

Aside from the large capital expense of building nuclear power plants, there’s the question of investing in nuclear R&D.

Holdren noted that it’s difficult to justify the cost of fusion R&D, but what about the larger amount of money spent on fission R&D?

Researchers Arnulf Grubler and Keywan Riahi argue in a paper in the new journal Carbon Management that, in terms of bang for the buck, we are spending too much on fission R&D.

The researchers assessed various technologies to determine their relative importance to future climate mitigation efforts. They used the results to analyze national energy technology R&D budgets and found that those budgets are out of balance. “We identify a significant mismatch [in] current energy technology R&D portfolios,” the researchers wrote.

They found that energy efficiency R&D is the most underfunded of the technologies and nuclear R&D is the most overfunded.

Conventional wisdom has it that we need to fund research in non-fossil-fuel energy technologies with the goal of building stabilization wedges. This paper shows that we should look at what we’re getting for our R&D investments because not all wedges are created equal. In terms of cost-effectiveness, we should pay more attention to energy efficiency and recognize that nuclear is far from the best option.