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Duane Pendergast
October 11, 1989
CANDU Operations
Atomic Energy of Canada Limited
Sheridan Park Research Community
Mississauga, Ontario, L5K 1B2 

(Published in the CNS Bulletin, Canadian Nuclear Society, Vol. 11, No. 1, Spring 1990



We've heard a lot about the greenhouse effect from the popular press over the past year. It is difficult to separate fact from fiction on the basis of this information. A review of the scientific literature reveals that the concerns expressed are based on solid science. The primary cause is the carbon dioxide diffused throughout the global atmosphere by our accelerating combustion of fossil fuels as a source of energy.  

The world uses a lot of energy for electricity, heating, transportation and chemical processes. About one third is used for electricity production. Nuclear power makes a significant contribution to world electricity production of about 15 - 20% which translates to a small fraction of world energy supply. 

An evaluation of the potential of nuclear energy, and in particular the CANDU reactor system, to ameliorate the greenhouse effect through the worldwide generation of electricity and the replacement of other energy sources by electrical power generation is provided. Although the potential benefit is large the scale of conversion to nuclear power needed to significantly influence the greenhouse effect is so large that even the nuclear industry has barely dared to contemplate the implications. 

Nuclear power is perceived by many to be unsafe. The greenhouse effect also poses a significant threat to the world population. It is incumbent on the nuclear industry and those who wish to preserve the environment to establish the risks and costs posed by nuclear power in the context of other risks and costs which confront us. The conjecture is that when this is done in a comprehensive manner nuclear energy will be seen as the safe economic energy supply option.   


We've heard a lot about the greenhouse effect from the press and defenders of the earth and environment since last summer. These are essentially the same people who promoted wind and solar power fifteen years ago and convinced governments to fund large research projects. Nothing significant has come of this effort. 

Three or four years ago my wife and I drove back from the West and encountered several huge windmills on the bank of the Columbia river. They loomed on the skyline for an hour's driving. A few months ago I read that they'd been sold as scrap. That symbol of the alternative energy dream is typical. Those large projects have simply re-demonstrated knowledge we've had for decades - wind and solar power can provide small quantities of energy for special purposes. Modern technology, engineering materials and design can wring a little more energy from the wind and the sun. 

The disappointing performance of that heavily ballyhooed "alternative energy technology" has led me to question whether the greenhouse effect is real or just another release of hot air from a small group of overly enthusiastic  crusaders. If it is real can nuclear energy possibly make a difference? In a superficial sense it can, since nuclear energy is a small contributor to the greenhouse effect. Can nuclear power really significantly replace fossil fuels with the great diversity of energy applications? How many nuclear plants are needed? Do we have enough fuel for them? Are construction materials available in sufficient supply?  

The deluge of information we've been exposed to is in the form of disconnected snippets. I decided much of what I was reading and hearing didn't make sense, so I decided to review the situation myself to get sufficient information to form a considered opinion as to the reality of the greenhouse effect. It turns out that a large body of soundly based knowledge of the climate and energy supplies is available for that purpose.  


Here is the situation as summarized from Professor Hare[1] of our own Ontario Nuclear Safety Review. 

* Global surface atmospheric temperatures will increase between 1.5 and 4.5 degrees C over the next 40 years - based  on the equivalent of doubling carbon dioxide in the atmosphere. (There are several other trace gases in the atmosphere as a result of mans activities. These contribute about as much to atmospheric heating as carbon dioxide. The "equivalent of doubling carbon dioxide" is thus taken to be a 50% increase in atmospheric carbon dioxide throughout this discussion.)

                        * High latitudes will warm the most with warmer winters. Equatorial regions will warm to a lesser degree. 

                        * Its likely that soil moisture will be less in mid latitudes - which include the chief wheat and corn growing areas. 

                        * Sea-level may rise between 20 and 140 cm during the warming. 

                         * These predictions are based on estimates of energy use and elaborate modelling of economic and ocean-atmospheric systems.

Professor Hare states that "this might mislead a listener unaccustomed to geophysical magnitudes". I think he means it sounds like a trivial effect . I agree. In fact it sounds so trivial that many Canadians express appreciation for the warmer winters the greenhouse effect is expected to bring. Quebec may be better able to grow grapes[2]. Professor Hare goes on to state; "I have no doubt that we are discussing the central environmental problem of our times". He and many other climatologists clearly believe this is a very serious problem and that adapting to these changes will pose great hardship. What is really driving their concern? What is all the fuss about? 


Oxygen and nitrogen, the main components of the atmosphere, are transparent to radiation to and from the earth's surface. Water vapour, carbon dioxide and other trace gases in the atmosphere are transparent to energy coming from the sun but absorb reradiated energy from the earth's surface. This heats the atmosphere in a manner somewhat analogous to the heating of your car in the sun - or a greenhouse.  

Carbon dioxide levels in the atmosphere are measurably increasing. Other greenhouse gases are increasing as well and provide a comparable heating effect. 

Computer modelling of this radiative heating effect along with solar heat input variations, atmosphere to ocean energy exchange, atmosphere and ocean circulation, cloud cover effects and other influences provide the predictions leading to the summary from Professor Hare. His summary is based on the somewhat arbitrary assumption that greenhouse gases released to the atmosphere will be equivalent to doubling of carbon dioxide levels prevailing about a hundred years ago. Actual levels will be strongly dependent on world economies and energy use patterns. "Best estimate" projections lead to a doubling in about 50 years. 


Models of physical processes are only helpful to the extent that they are based on reality and give results which agree with reality. Complex computer models in particular need comparison with measured reality to provide believability (validation).

Carbon dioxide levels are most assuredly increasing. Figure 1 shows measured results back to 1870 retrieved from various sources and presented by Callendar[3] in 1956. An increase was already evident then. Figure 2[4] shows a subsequent continuity of rising levels at three locations remote from sources of carbon dioxide in the northern hemisphere from 1960 to 1988. Other studies have shown similar increases around the world. Carbon dioxide levels in the southern hemisphere lag behind northern levels. This is attributed to the relatively slow mixing[5] of the northern atmosphere, where 90% of fossil fuel emissions take place, with the southern atmosphere. (Does anyone remember the movie "On the Beach"?)

These recent rapid rises correlate with increasing fossil fuel use as demonstrated in Figure 3[6]. Figure 3 also gives an indication of carbon dioxide releases from changing land use including deforestation. Although it's hard to tell from the popular press which is most significant, the information in Figure 3 suggests that fossil fuels must be the major contributor to atmospheric carbon dioxide. Measurement[7] of carbon 14 which is formed in the atmosphere and deposited in tree rings provides additional evidence that fossil fuels are a major source. Carbon 14 is not present in fossil fuels which are very old but is present in tree rings which are generally much younger than the 5730 year half life of carbon 14. The measurements indicate that carbon 14 levels in the atmosphere decreased until 1952 when nuclear bomb tests substantially increased atmospheric levels of carbon 14. This dilution of carbon 14 levels establishes little doubt that fossil fuels are the major contributors to atmospheric carbon dioxide. A great deal of information on the quantities[8] and flows[9] of

carbon from fossil fuels, plants, the atmosphere and the oceans is shown in Figure 4[10]. We can deduce from the information contained in Figure 4 that; 

*The atmosphere contains about 700 billion tons of carbon in carbon dioxide. 

*Plants consume - and release the carbon dioxide in the atmosphere in about seven years. Some of this exchange involves interchange with the earth's soil through death and decay of plants.

*The oceans also absorb and release the atmosphere's carbon dioxide content in about seven years.

*Plants contain about as much carbon as the atmosphere.

*About 7 billion tons of carbon as carbon dioxide is released to the atmosphere annually. About 5 billion tons of this is from fossil fuels and the remainder is from changing land use. Four billion tons are absorbed by the oceans leaving an additional 3 billion tons to accumulate in the atmosphere each year.

*Recoverable fossil fuels contain about 7 times as much carbon as the atmosphere.

*The oceans contain about 70 times as much carbon as the atmosphere. A small fraction of this carbon is close to the surface and the atmosphere.

*The earth's soil contains substantially more carbon than the atmosphere. 

This information reveals the difficulty of modelling future atmospheric carbon dioxide content. Not only is the annual addition to the atmosphere small in comparison with net flows to and from plants and oceans - future energy use is not easy to predict either. Engineers and scientists thus seem to base their estimates of future carbon dioxide content on extrapolations  of measured atmospheric carbon dioxide adjusted for revisions in energy use patterns. "Best" estimates  of short term projections suggest an effective (taking into account the other greenhouse gases) doubling of carbon dioxide by about the year 2030[11]. Thus many detailed projections of consequence focus on a doubling of carbon dioxide. Most of the fossil fuel reserves would remain for further additions to the atmosphere. Some discussion of validation studies  follows. 

The estimated increase in mean temperature for the past 100 years when records have been kept and fossil fuel has been burnt is only about 0.5 degree C. This is lost in normal weather variations and on our senses. Nevertheless models for mean global temperature increase show a degree of agreement with measurements when volcanic effects, solar heating changes ,and  heat exchange with the oceans is factored in.

 Work done by Hansen in 1980 is shown in Figure 5[12]. The agreement with measurement is quite satisfying but is not taken as proof that carbon dioxide is increasing the temperature. Another two decades of "business as usual" was expected to yield a clear signal in 1984[13]. We should thus expect to clearly measure greenhouse heating shortly after the year 2000. 

Three dimensional time dependent computer models have evolved as a byproduct of numerical weather prediction models. These are the only source of predictions of local environmental changes as a consequence of carbon dioxide induced heating. Stephen Schneider discusses validation of these models in a recent issue of Trends in Computing[14]. He compares model predictions with seasonal variations of climate and with changes occurring following the last ice age. The seasonal variations are very satisfying to those of us who have used related models to predict some aspects of reactor operation.  The post ice age predictions are -- well?? - a bit fuzzy! At least to those of us who model the better defined fluid flow conditions relating to nuclear reactors! Schneider goes on to discuss three dimensional models of the greenhouse effect and concludes that they are not only too consumptive of computer time to predict the next century but are also not yet sufficiently trustworthy. 

I found another article from Scientific American[15] which discusses recently[16] obtained ice cores going back more than 150,000 years to be particularly interesting. Gas trapped in bubbles in the ice provides evidence of carbon dioxide and methane levels as a function of time. Directly measured atmospheric carbon dioxide levels (Figures 1 and 2) correlate well with the ice core bubble measurements (Figure 6[17]) as far back as 1870. Oxygen 16 to oxygen 18 ratios in the core give a measure of past temperatures as well.  

Temperature and carbon dioxide levels rise and fall together (Figure 7[18]) although climatologists do not assign a cause and effect relationship to this observation. I was particularly impressed by the small variation of carbon dioxide over the past 160,000 years compared with the potential changes man could bring about through enthusiastic increases in consumption of our fossil fuel reserves. The ice core data seems to be great material for further validation of models. 

I've noted that climatologists seem to be particularly concerned with being accused of "crying wolf". The press has picked up on the consensus position outlined in Section 2 above. This is a pretty middle of the road position. It's a wide road. Predictions of climate and fuel use are quite uncertain. The big picture seems to be that there is sufficient fossil fuel and we're currently using it quickly enough to make the greenhouse effect much worse in the long run than the consensus 50 year projection. Another one or two hundred years of fossil fuel use at current rates, or higher, could cause much larger heating which in turn would result in more flooding and other adverse effects. I suspect the uncertainties and worse case scenarios  are driving the strong expressions of concern from our climatologists. 


The world uses a lot of energy for electricity, heating, transportation and chemical processes. Data on world generating capacity[19] and the fraction used for electricity generation[20] suggests that seventy five hundred 1000 megawatt power plants would be able to replace all this energy . I'm not quibbling over capacity factors or efficiency of various applications. About 1/3 of world energy consumption is used for electricity production at present. Thus twenty five hundred 1000 megawatt nuclear power plants would replace existing electricity generating capacity. 

Nuclear power already makes a significant contribution to electricity production[21] of around 15%. Water power contributes 20%. Fossil fuels contribute the rest including most heating, transportation, and  process needs. 

Nuclear and water power are potential solutions to the greenhouse problem as their operation contributes very little carbon dioxide to the atmosphere. Since large water power sites are limited only nuclear power remains as a "here now" technology to replace power from polluting fossil fuel plants. Of course there is hope for new sources of energy such as a breakthrough in solar cells or the tapping of fusion power. Do you remember cold fusion? 

We've built about 500 plants in the short time we've been dabbling in nuclear power. I don't think it takes a big stretch of imagination to consider building another 2000 of them to replace current means of electricity production. This would reduce carbon dioxide emissions about 25% but would not go very far in ameliorating the greenhouse effect on its own. In fact this would amount to only a 10% to 15% reduction of current greenhouse gas production since it would have little effect on the other greenhouse gases man is responsible for generating. 

Converting some systems such as transportation to nuclear power to further ameliorate the greenhouse effect requires more effort. Hydrogen fuel generation may be one feasible route to maintaining existing lifestyles and population. Nuclear plants could generate the electricity to produce the hydrogen. The cost of needed power plants is judged to be within the realm of possibility even by those who are not in favour of a "nuclear response[22]" (I'm not sure I like the authors choice of words) to the greenhouse problem. I think feasibility must take into account the massive economic feedback effects which would result from  such a huge commitment to nuclear power. What else might we do to ameliorate the greenhouse effect?  


Grow more forests? The data from Figure 4 indicates existing forests contain about 1/10 as much carbon as the reserve of fossil fuel. If we could force the growth of 10 times the current forest mass over the projected life of fossil fuel reserves (500 - 1000 years) and stockpile the wood we would solve the carbon dioxide problem while happily burning up all of our fossil fuel reserves. One author[23] suggests additional forest three times the size of Alaska would absorb the three billion tons of carbon dioxide annually added to the atmosphere at current rates. A greater amount of formerly forested land is thought to be available for this purpose. 

Conservation is cited as a major means of coping with the greenhouse. This has substantial potential. The energy crisis of the early 1970's, resultant high prices, and legislated automotive fuel economy  did reduce oil use[24] temporarily. Bill Keepin and Gregory Kats present an analysis[25] which purports to show that efficiency improvement alone is 2.5 to 10 times more cost effective in reducing carbon dioxide than revitalizing nuclear power. These gentlemen are from the Rocky Mountain Institute which is not known as a promoter of nuclear power. 

Others advocate a switch from coal to natural gas. This reduces carbon dioxide, for a given energy output, by about half[26]. I see this as a short term partial solution until natural gas runs out. 


The title of this article asks if the real nuclear safety story hinges on the greenhouse effect. Where does safety come into this? Continued heavy burning of fossil fuels poses a significant risk to world population through greenhouse heating and pollution of our living space. Nuclear power is the only credible low carbon dioxide producing alternative in hand in sufficient quantities to replace fossil fuel. Waste products from the nuclear fuel cycle are sufficiently small to be contained. If risk from nuclear power is smaller than risk from fossil fuel then nuclear power is the safer energy source. 


We are burning fossil fuels at an unprecedented rate and releasing carbon dioxide to the atmosphere which natural processes cannot remove quickly enough to avoid increased carbon dioxide in the atmosphere. Computer models indicate a carbon dioxide induced heating effect which climatologists believe will lead to profound changes in our way of life. 

Nuclear power may well have a major role to play in reducing carbon dioxide emissions from energy production. The nuclear industry has a responsibility to understand and propagate understanding of the role nuclear energy has to play in protecting the environment. In view of the complexity of the technical problem and its intertwined relationship with the world economy this will be a difficult task. I raised some questions on nuclear fuel and material supplies in the introduction. I suspect this will be queried by our critics in coming months and intend to follow up this note with a review of nuclear material availability. I also mentioned conservation in Section 6. I intend to examine the credibility of that alternative. 


I set out to evaluate the reality of the greenhouse effect in the light of my earlier disappointment with the alternative energy movement. I'm convinced the hue and cry we've been hearing for the past year is based on solid research. A systematic research program extends back in time about 30 years and continues. The greenhouse issue does have more substance than windmills and solar power. 

Nuclear power has substantial potential to ameliorate the greenhouse effect while maintaining us in the style to which we have become accustomed. In fact nuclear power may well turn out to be the safe energy option. 


Some useful and readable articles have been published since I prepared this. In particular I recommend a series of three articles appearing  in Popular Science magazine starting with the August issue. The first two deal with an evaluation of the reality of the greenhouse predictions and an examination of the science of the greenhouse effect. The third article outlines and evaluates potential actions to ameliorate climate change due to man's activities. 

The September 11th issue of The New Yorker includes a near book length article titled, "The End of Nature". This informative and somewhat melancholy review concludes that we should curtail our endless growth and give nature a second chance. 

The September issue of Scientific American is devoted to the theme, "Managing Planet Earth". Articles on the climate, the atmosphere and energy use are of particular relevance to the greenhouse effect. 

Finally, should you wish to get into this in detail, Reference 5 below provides a lot of information and several hundred additional references to the scientific literature. 


My thanks to Ernie Siddall and Professor F. Kenneth Hare for technical reviews and helpful advice, John MacPherson for his technical editing and to Jo-Anne Prinzen for her help with finding information. 


[1].Hare, F. Kenneth, The Global Greenhouse Effect in: The changing atmosphere : implications for global security, Proceedings of the Toronto Conference on  the Environment, World Meteorological Association, WMO - 710, Toronto,  27-30 June 1988, pp. 59-68.

[2].Singh, B., The Implications of Climate Change - Quebec, Environment Canada, 1988.

[3].Callendar, G.S., On the Amount of Carbon Dioxide in the Atmosphere, Tellus X(1958) II, pp. 243-248.

[4].Loc. cit. 1. - Figure 2 is adapted from Figure 1 of Ref.1.

[5].Bolin, B., 1986: How Much Carbon Dioxide Will Remain in the Atmosphere? In: The Greenhouse Effect, Climatic Change, and Ecosystems, Bolin, B. et al (Eds.), SCOPE 29, Wiley.

[6].Houghton, R. A., and G. M. Woodwell, Global Climatic Change, Scientific American, Vol.260, No. 4, April 1989.

[7].Bolin, B., 1986: How Much Carbon Dioxide Will Remain in the Atmosphere? In: The Greenhouse Effect, Climatic Change, and Ecosystems, Bolin, B. et al (Eds.), SCOPE 29, Wiley, Sect 3.3.3, pp. 101.

[8].Rotty, R. M., The Nature of the CO2 Problem: Certainties and Uncertainties, Environmental Progress, Vol. 3, No. 4, November, 1984.

[9].Houghton, R. A., and G. M. Woodwell, Global Climatic Change, Scientific American, Vol.260, No. 4, April 1989, Figure 3 adapted from figure on page 39.

[10].Figure 4 is based on information from Reference 8 and Reference 6.

[11].Hare, F. Kenneth, The Global Greenhouse Effect, Proceedings of the Toronto Conference on  the Environment, World Meteorological Association, WMO - 710, Toronto,     1988, Sect. 3.

[12].Figure 5 is adapted from Reference 8

[13].Rotty, R. M., The Nature of the CO2 Problem: Certainties and Uncertainties, Environmental Progress, Vol. 3, No. 4, November, 1984, pp. 257.

[14].Schneider, S.H., Climate Modelling, Trends in Computing, Vol.1, No. 1, pp. 132-139: Reprinted from Scientific American, May, 1987.

[15].Houghton, R. A., and G. M. Woodwell, Global Climatic Change, Scientific American, Vol.260, No. 4, April 1989, pp. 39-40.

[16].Barnola, J. M., et al, Vostok Ice Core Provides 160,000 - Year Record of Atmospheric Carbon Dioxide., Nature, Vol. 329, No. 1, (October)1987

[17].Neftel, A., et al, Evidence from Polar Ice Cores for the Increase in Atmospheric Carbon Dioxide in the past two Centuries, Nature, Vol. 315, No. 2, (May)1985:  Adapted from Figure 1.

[18].Figure 7 is adapted from Reference 16.

[19].FOCUS, Atomic Energy of Canada Limited, AECL 9726 - 2, Fall/Winter 1988, Part C, Table 14.

[20].Loc. cit. 19, Part C, Table 16.

[21].Loc. cit. 19, Part C, Table 9.

[22].Keepin, Bill and Gregory Kats, Greenhouse Warming: Comparative Analysis of Nuclear and Efficiency Abatement Strategies, Energy Policy, (December)1988.

[23].Houghton, R. A., and G. M. Woodwell, Global Climatic Change, Scientific American, Vol.260, No. 4, April 1989, pp. 44.

[24].Rotty, R. M., The Nature of the CO2 Problem: Certainties and Uncertainties, Environmental Progress, Vol. 3, No. 4, November, 1984, Figure 3.

[25].Keepin, Bill and Gregory Kats, Greenhouse Warming: Comparative Analysis of Nuclear and Efficiency Abatement Strategies, Energy Policy, (December)1988

[26].Keepin, Bill and Gregory Kats, Greenhouse Warming: Comparative Analysis of Nuclear and Efficiency Abatement Strategies, Energy Policy, (December)1988, Endnote 26.


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