Originally published in the International Herald Tribune, October 17, 2008.
Copyright © Daniel B. Botkin 2008.

John McCain has called for building 45 new nuclear power plants by 2030 and 100 eventually. Barack Obama’s Web site says, “It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power from the table.”
But to what extent can nuclear power really help achieve energy independence?

There’s a problem about nuclear energy that gets little attention. At present, fossil fuels provide 87 percent of the world’s total energy while nuclear power plants provide just 4.8 percent. (All nuclear power plants currently generate electricity, accounting for about 15 percent of world electricity generation, while fossil fuels produce almost 67 percent of the electricity.)

The best estimates put the amount of uranium that can be mined economically (what geologists call the reserves) at about 5.5 million metric tons, and according to the International Atomic Energy Agency, today’s nuclear power plants use 70,000 metric tons a year of uranium. At this rate of use, the uranium that could be mined economically would last about 80 years.

Suppose it were possible to replace all fossil fuels with nuclear power. Suppose that we could use nuclear energy to make liquid and gas fuels to power vehicles, and could do this quickly using conventional nuclear power plants.

We would have to build enough plants to increase energy production by 17.4 times, which means using 1.2 million tons of uranium ore each year. At that rate of use, the reserves of uranium would be used up in less than five years.

Geologists also estimate that there are about 35 million tons of uranium out there regardless of the cost of mining it (geologists call this identified resources). With nuclear power replacing all fossil fuels, even these would be used up in 29 years.

Thus, if the goal is to counter global warming by replacing all fossil fuels with nuclear power, this goal cannot be met.

Advocates of nuclear power point out that it doesn’t have to replace all other sources of energy. Let’s consider that approach.

At a recent meeting, the Group of Eight major industrial countries agreed to reduce carbon emissions 50 percent by 2050. Suppose nuclear energy increased just enough each year to enable fossil-fuel use to decline at a constant annual rate, to 50 percent by 2050, while nuclear power therefore increased to provide 50 percent of the world’s energy.

At this rate of use, uranium reserves would run out by 2019, and the estimated maximum of 35 million metric tons of uranium in identified resources would run out by year 2038, gaining us less than two decades.

There are some important caveats. Exploring for minerals is done on an as-needed basis, and large areas of the world may have been little explored for uranium. Every mining geologist and mine corporation executive will tell you that estimates of total reserves of a mineral are just that – estimates – and that the reserves of many minerals always increase over time.

This approach may be all right for the planning time of mining companies, but it won’t work for a long-term global energy strategy based on adequate supplies of uranium.

Considering the enormous costs of building the large number of nuclear power plants that are contemplated to replace fossil fuels, the United States would be courting disaster if it chose this route with nothing but blind faith that there may be a lot more uranium out there if we only look for it.

We need to know a lot more about available uranium resources and where they are. If they are in unfriendly countries, they might not be available at all.
Nuclear power advocates also argue that it is possible to recover significant amounts of uranium from spent fuel. According to the International Atomic Energy Agency, “In 2004, two-thirds of the uranium used was newly mined; the rest came from civil and military stockpiles, spent fuel reprocessing and re-enrichment of depleted uranium.”

But the amount from spent fuels is not specified, and a reprocessing program to deal with 1.2 million tons of used uranium would be a major undertaking, perhaps not technologically feasible in the near future.

Others suggest that breeder reactors, which produce more nuclear fuel than they use, will solve the problem.

The United States experimented with a few breeder reactors from 1964 to 1994, but they were shut down or work on them halted in the 1990s.
Other nations have tried building them, and some are considering or developing them. But to my knowledge perhaps only one or two breeder reactors are in use and providing electrical energy anywhere in the world, and these are probably not “breeding.”

There are reasons for this: The technology is not there yet, and the reactors are dangerous in themselves, even without considering their potential use in making atomic weapons. They are the kind of nuclear reactors that everybody fears Iran or North Korea might build and use to make atomic bombs.
In sum, the breeder-reactor route, if it is practical at all, is a long way in the future as a major contributor to the world’s energy, and certainly not a way to reduce our dependence on fossil fuels now or in the near future.

The bottom line: From what is known about resources of uranium and the present and future state of nuclear power plants, there is no way that nuclear power can play a dominant role in the world’s energy supply.

This is not to say that it could play no role in a mixed strategy involving many kinds of energy, only that those who continue to press for a greater role for nuclear power must first show that there will be enough uranium to assure that thousands of nuclear power plants built at enormous cost would not soon stand idle – and leave our economy standing idle too.

by Daniel B. Botkin, Henrik Saxe, Miguel B. Araújo, Richard Betts, Richard H. W. Bradshaw, Tomas Cedhagen, Peter Chesson, Terry P. Dawson, Julie R. Etterson, Daniel P. Faith, Simon Ferrier, Antoine Guisan, Anja Skjoldborg Hansen, David W. Hilbert, Craig Loehle, Chris Margules, Mark New, Matthew J. Sobel, And David R. B. Stockwell. Published in BioScience 57(3): 227-236.

In 2004 a group of scientists, including myself, met and discussed what needed to be done to improve the ability to forecast the possible effects of global warming on biodiversity.  The result was a paper published in BioScience, the journal of the American Institute of Biological Sciences (AIBS).

In that paper, we proposed a “Quarternary Conundrum” — we found that the fossil record gave results about climate change and biodiversity that did not agree with modern forecasts.  Here is what we wrote about that idea.  (If you are interested in more from this paper, let me know and I will post more of it, or you can obtain it from AIBS.)

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Current forecasting methods suggest that global warming will cause many extinctions, but the fossil record indicates that, in most regions, surprisingly few species went extinct during the Quaternary (from approximately 2.5 million years BCE to the present)—in North America, for example, only one tree species is known to have gone extinct (Bush and Hooghiemstra 2005). Large extinctions were reported mainly for tree species in northern Europe (68% loss of tree genera; Svenning and Skov 2004) and for large mammals (> 44 kg) in the Northern Hemisphere (MacPhee 1999).We refer to this contrast between the implications of modern forecasts and the observed fossil record as the “Quaternary conundrum.” The resolution of this conundrum is key to improving forecasts of climate-change effects on biodiversity. Among the possible explanations are that climate change during the Quaternary was greatly different from climate change forecasted for the future; that genetic and ecological mechanisms, not accounted for in formal forecasting methods, allow the persistence of many species even under rapid climate change; and that factors in addition to climate change could decrease rates of extinction.

Some recent ecological genetics research further deepens the puzzle. For example, the risk of extinction for a species in response to climate change depends on the demography and evolution of genetically differentiated populations across their geographic ranges. If populations are locally adapted, climate change will cause conditions to deteriorate across the species’ range, rather than just at the margins of the range. Modern reciprocal transplant experiments, in which spatial gradients in climate serve as proxies for temporal climate change in the future, show that these fitness losses can be large (Rehfeldt et al. 1999, Etterson 2004). For example, a reciprocal transplant experiment on lodgepole pine in Canada indicated that global warming would slow tree growth and increase mortality, resulting in a 20% loss of productivity (Rehfeldt et al. 1999). Likewise, a study of a prairie annual in the Great Plains of the United States showed a 30% reduction in seed production in climates similar to those predicted for future decades. Ecological genetic data, in each of these cases, predicted different rates of adaptive evolution in different parts of the species’ range (e.g., rear and leading edge; Hampe and Petit 2005) but generally suggested that evolutionary rates would be slower than the anticipated rate of climate change (Etterson and Shaw 2001, Rehfeldt et al. 2002).

Until recently, it was thought that past temperature changes were no more rapid than 1 degree Celsius (^oC) per millennium, but recent information from both Greenland and Antarctica, which goes back approximately 400,000 years,indicates that there have been many intervals of very rapid temperature change, as judged by shifts in oxygen isotope ratios. Some of the most dramatic changes (e.g., 7^oC to 12^oC within approximately 50 years; Macdougall 2006) are actually of greater amplitude than anything projected for the immediate future. Although these changes were probably not equally severe everywhere on the globe, a well-documented rapid warming did occur around the shores of the North Atlantic at the end of the last glaciation, when melting of the ice cover on the ocean suddenly allowed the Gulf Stream to reach the shores of northern Europe. There, temperatures rose rapidly, perhaps as rapidly as anticipated today for the next several decades (Huntley et al. 1997).

What could explain the Quaternary conundrum? One possibility is that migrations were faster than has been thought possible. A large literature examines late-Quaternary range shifts deduced from the pollen record, and recent papers consider models and seed-dispersal mechanisms that may account both for migration across geographic barriers and for rapid invasion of new territory. Sparse populations of several tree species are now known (from genetic and macrofossil evidence, supplemented by detailed analysis of mapped pollen data) to have persisted during the last glacial maximum in regions where very few, if any, pollen grains have been observed—regions that for this reason would be judged well outside the climate envelope for these species (Tomaru et al. 1998, Brubaker et al. 2005, McLachlan et al. 2005, Magri et al. 2006). These populations serve as advance colonists, allowing rapid population growth in newly available habitat.

A second explanation is that low extinction rates during Quaternary climate change may be partially attributable to ongoing adaptive evolution. Theoretical models suggest that adaptive evolution can enhance the persistence of populations in a changing environment even when migration is possible (Bürger and Lynch 1995). And rapid genetic adaptation to climate has already been documented for a few wild organisms for which long-term studies of field populations have been conducted (reviewed in Bradshaw and Holzapfel 2006). Invasive species have also evolved since their arrival in a new habitat in the 20th century, at surprisingly rapid rates of evolution (e.g., Huey et al. 2000).

A long-standing controversy regarding the role of people in Quaternary extinctions of large mammals speaks to the difficulty of quantifying impacts of multiple factors on species loss. The high extinction rate of large mammals has been widely recognized since the 19th century, and extinctions of large mammals and island birds over the past 100,000 years have been the subject of much conjecture. Paul Martin has made the now well-known case that the timing of extinctions followed human dispersal from Afro-Asia to other parts of the globe and that these extinctions resulted from human “blitzkrieg” overkill (Martin and Steadman 1999). But careful analysis of well-documented extinctions in Beringia suggests that human hunting was superimposed on a preexisting trend of diminishing animal population density (Shapiro et al. 2004, Guthrie 2006). These data suggest that the interaction of environmental change and human resource use can have a larger negative impact on biodiversity than either factor alone.

Copyright © American Institute of Biological Sciences, posted with permission.