By Pushker Kharecha and James Hansen,

NASA Goddard Space Flight Center



Human-caused climate change and air pollution remain major global-scale problems and are both due mostly to fossil fuel burning. Mitigation efforts for both of these problems should be undertaken concurrently in order to maximize effectiveness. Such efforts can be accomplished largely with currently available low-carbon and carbon-free alternative energy sources like nuclear power and renewables, as well as energy efficiency improvements.



Figure 1. Cumulative net deaths prevented assuming nuclear power replaces fossil fuels. The top panel (a) shows results for the historical period in our study (1971-2009), with mean values (labeled) and ranges for the baseline historical scenario. The middle (b) and bottom (c) panels show results for the high-end and low-end projections, respectively, of nuclear power supply estimated by the IAEA (ref. 4) for the period 2010-2050. Error bars reflect the ranges for the fossil fuel mortality factors listed in Table 1 of our paper. The larger columns in panels (b) and (c) reflect the all-coal case and are labeled with their mean values, while the smaller columns reflect the all-gas case; values for the latter are not shown because they are all simply a factor of about 10 lower (reflecting the order-of-magnitude difference between the mortality factors for coal and gas). Countries/regions are arranged in descending order of CO2 emissions in recent years. FSU15=15 countries of the Former Soviet Union and OECD=Organization for Economic Cooperation and Development. In a recently published paper (ref. 1), we provide an objective, long-term, quantitative analysis of the effects of nuclear power on human health (mortality) and the environment (climate). Several previous scientific papers have quantified global-scale greenhouse gas (GHG) emissions avoided by nuclear power, but to our knowledge, ours is the first to quantify avoided human deaths as well as avoided GHG emissions on global, regional, and national scales.

The paper demonstrates that without nuclear power, it will be even harder to mitigate human-caused climate change and air pollution. This is fundamentally because historical energy production data reveal that if nuclear power never existed, the energy it supplied almost certainly would have been supplied by fossil fuels instead (overwhelmingly coal), which cause much higher air pollution-related mortality and GHG emissions per unit energy produced (ref. 2).

Figure 2. Mean net deaths prevented annually by nuclear power between 1971-2009 for various countries/regions. Ranges not shown but are a factor of ~4 higher and lower than the mean values. Using historical electricity production data and mortality and emission factors from the peer-reviewed scientific literature, we found that despite the three major nuclear accidents the world has experienced, nuclear power prevented an average of over 1.8 million net deaths worldwide between 1971-2009 (see Fig. 1). This amounts to at least hundreds and more likely thousands of times more deaths than it caused. An average of 76,000 deaths per year were avoided annually between 2000-2009 (see Fig. 2), with a range of 19,000-300,000 per year.

Likewise, we calculated that nuclear power prevented an average of 64 gigatonnes of CO 2 -equivalent (GtCO 2 -eq) net GHG emissions globally between 1971-2009 (see Fig. 3). This is about 15 times more emissions than it caused. It is equivalent to the past 35 years of CO 2 emissions from coal burning in the U.S. or 17 years in China (ref. 3) — i.e., historical nuclear energy production has prevented the building of hundreds of large coal-fired power plants.

To compute potential future effects, we started with the projected nuclear energy supply for 2010-2050 from an assessment made by the UN International Atomic Energy Agency that takes into account the effects of the Fukushima accident (ref. 4). We assume that the projected nuclear energy is canceled and replaced entirely by energy from either coal or natural gas. We calculate that this nuclear phaseout scenario leads to an average of 420,000-7 million deaths and 80-240 GtCO 2 -eq emissions globally (the high-end values reflect the all coal case; see Figs. 1 and 3). This emissions range corresponds to 16-48% of the "allowable" cumulative CO 2 emissions between 2012-2050 if the world chooses to aim for a target atmospheric CO 2 concentration of 350 ppm by around the end of this century (ref. 5). In other words, projected nuclear power could reduce the CO 2 mitigation burden for meeting this target by as much as 16-48%.

Figure 3. Cumulative net GHG emissions prevented assuming nuclear power replaces fossil fuels. The three panels are ordered the same as in Fig. 1, except that mean values for both the all coal and all gas cases are labeled. Error bars reflect the ranges for the fossil fuel emission factors listed in Table 1 of our paper. The largest uncertainties and limitations of our analysis stem from the assumed values for impacts per unit electric energy produced. However, we emphasize that our results for both prevented mortality and prevented GHG emissions could be substantial underestimates. This is because (among other reasons) our mortality and emission factors are based on analysis of Europe and the US (respectively), and thus neglect the fact that fatal air pollution and GHG emissions from power plants in developing countries are on average substantially higher per unit energy produced than in developed countries.

Our findings also have important implications for large-scale "fuel switching" to natural gas from coal or from nuclear. Although natural gas burning emits less fatal pollutants and GHGs than coal burning, it is far deadlier than nuclear power, causing about 40 times more deaths per unit electric energy produced (ref. 2).

Also, such fuel switching is practically guaranteed to worsen the climate problem for several reasons. First, carbon capture and storage is an immature technology and is therefore unlikely to constrain the resulting GHG emissions in the necessary time frame. Second, electricity infrastructure generally has a long lifetime (e.g., fossil fuel power plants typically operate for up to ~50 years). Third, potentially usable natural gas resources (especially unconventional ones like shale gas) are enormous, containing many hundreds to thousands of gigatonnes of carbon (based on ref. 6). For perspective, the atmosphere currently contains ~830 GtC, of which ~200 GtC are from industrial-era fossil fuel burning.

We conclude that nuclear energy — despite posing several challenges, as do all energy sources (ref. 7) — needs to be retained and significantly expanded in order to avoid or minimize the devastating impacts of unabated climate change and air pollution caused by fossil fuel burning.

References

1. Kharecha, P.A., and J.E. Hansen, 2013: Prevented mortality and greenhouse gas emissions from historical and projected nuclear power. Environ. Sci. Technol. , in press, doi:10.1021/es3051197.

2. Markandya, A., and P. Wilkinson, 2007: Electricity generation and health. Lancet , 370, 979-990, doi: 10.1016/S0140-6736(07)61253-7.

3. Boden, T. A., G. Marland, R.J. Andres, 2012: Global, Regional, and National Fossil-Fuel CO 2 Emissions . Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A., doi:10.3334/CDIAC/00001_V2012.

4. International Atomic Energy Agency, 2011: Energy, Electricity and Nuclear Power Estimates for the Period up to 2050: 2011 Edition . IAEA Reference Data Series 1/31. Available at http://www-pub.iaea.org/MTCD/Publications/PDF/RDS1_31.pdf

5. Hansen, J., P. Kharecha, Mki. Sato, V. Masson-Delmotte, et al., 2013: Scientific prescription to avoid dangerous climate change to protect young people, future generations, and nature. PLOS One , submitted.

6. GEA, 2012: Global Energy Assessment — Toward a Sustainable Future . Cambridge University Press, Cambridge, UK and New York, NY, USA and the International Institute for Applied Systems Analysis, Laxenburg, Austria. Available at http://www.globalenergyassessment.org.