THE COOLING OF THE GREENHOUSE AND  NUCLEAR ENERGY 

DUANE PENDERGAST
 
Process and Safety Engineering Department
AECL CANDU
Atomic Energy of Canada Limited
Sheridan Park Research Community
Mississauga, Ontario, L5K 1B2

(Published in the proceedings of the 11th Annual Conference of the Canadian Nuclear Society, Toronto, Canada, 3‑6 June 1990)

(Copyright assigned to the Canadian Nuclear Society)

ABSTRACT 

The enhanced greenhouse effect which is caused largely by gases released during the combustion of fossil fuels is expected by many researchers to lead to climate warming. The societal costs of predicted warming provide a strong incentive to reconsider nuclear fission as a major source of relatively greenhouse gas free energy. The case for and against global warming presented in the literature is reviewed. The strength of the case for warming is found wanting at present. Continuing model validation and observation of trends will, in time, resolve much of the current uncertainty of predictions. In the meantime it is incumbent on the nuclear industry to clearly establish the potential for fission derived energy to replace energy currently provided by fossil fuels.  

INTRODUCTION 

Scientists have been predicting, for several decades[1], that rising carbon dioxide levels in the atmosphere will lead to increased average world surface temperature. Early articles on this "greenhouse" effect projected that the warming would be beneficial as plant growth would be enhanced and the onset of an anticipated ice age could be delayed indefinitely. This initial optimism about the consequences of the greenhouse effect then gave way to concerns that human interference with the atmosphere might be harmful[2]. We've recently read an outpouring of concern from the media and the popular press that greenhouse warming is here and that we must start doing something to control it. For the past year or two the nuclear power industry has anticipated benefits from the media's discovery of the greenhouse effect. However expectations of quick public acceptance and imminent reactor sales are wearing off. The greenhouse climate is cooling, literally and figuratively, as estimates of the magnitude of warming decrease[3], fault is found[4] with modelling simulations, and scepticism of the public is reinforced by complacency arising from expectations that the effect can easily be avoided by conservation and efficient energy use. Furthermore, nuclear power is rejected by some[5],[6] as an inappropriate response to the greenhouse "problem". 

Fossil fuels are believed, by many, to be the major cause of observed increasing carbon dioxide levels in the atmosphere. The operation of nuclear power plants is acknowledged, even by those who believe nuclear power is not the way to achieve reduced global warming, to be relatively carbon dioxide free[7]. Why then would nuclear power be rejected as a solution? The simplistic rationale is that more efficient energy use is deemed to be more cost effective at present[8], and nuclear fuel supplies are inadequate to support the large scale production of nuclear power needed to significantly reduce carbon dioxide release to the atmosphere. 

Nuclear industry visionaries have identified the tremendous potential[9],[10] to replace fossil fuel energy with nuclear derived energy[11]. The greenhouse issue has raised the possibility that the massive conversion to nuclear energy, envisaged by them, is essential now. Recent media attention to the greenhouse effect has made it seem that a disastrous climate change is imminent. Is this really true? Can nuclear power plants meet the requirements of proposals to limit greenhouse gas releases? This article outlines a quest for answers to these questions from the scientific and engineering literature and the popular media. 

GREENHOUSE PREDICTION CREDIBILITY 

The prediction of increased temperatures world wide is based on expectations that man caused releases of carbon dioxide and other gases into the atmosphere will accumulate and lead to a trapping of heat in the atmosphere. Carbon dioxide is the major greenhouse gas in the atmosphere at present and contributes about half of the projected warming. There is some degree of dispute over the relative contribution of these gases expressed in the scientific literature. The role that deforestation plays through burning and loss of a carbon dioxide sink is also discussed a great deal. Nevertheless there are simple, very convincing, arguments in place to show that the combustion of fossil fuels plays the major role. The supplies of fossil fuels are also sufficiently large to potentially overwhelm other sources such as deforestation in the long run. The oceans are thought to have a great capacity to absorb carbon dioxide. They contain at present far more carbon dioxide than the stores of fossil fuels could possibly contribute. However, the oceans absorb carbon dioxide very slowly.

Figure 1[12] quantifies the role of various major carbon dioxide sources and sinks for the atmosphere. The bottom line is that carbon dioxide is building up in the atmosphere. A good deal of the buildup is due to fossil fuel combustion. Man has increased atmospheric carbon dioxide by about 25% in the past century. This rate of increase is far higher than has occurred in the past as can be inferred from air trapped in ancient ice. The scientific evidence is convincing even to the layman. 

The cooling of interest in the greenhouse phenomena seems to be focused, not on doubts associated with the buildup of greenhouse gases, but on the predictions of the heating effect from them. The phenomena of greenhouse heating is very complex with interrelations and feedback effects from many variables. Predictions of atmospheric heating have thus become almost entirely dependant on computer simulation models. The nuclear industry has plenty of experience with the vagaries and difficulties of computer modelling. A lack of understanding and appreciation of these models has played a role in the loss of public credibility in nuclear power. Opponents have simply argued that computer models are too complex and unpredictable to be believed. We may already be seeing the effects of a similar reaction to the climate models which predict greenhouse warming. A brief examination of the predictions and measurements used for model validation is warranted. 

Figure 2[13] shows the atmospheric temperature record from meteorological measurements over the last century. The plotted points represent a five year mean based on a linear average for the five years centered on the points. A modest increase of 0.6⁰C is evident with some hesitations along the way. This increase is consistent with heating predictions from climate models.  

Figure 3[14] shows the output from a control run of a climate simulation model. This run is based on the assumption of constant greenhouse gas levels, but allows for varying heat exchange with the ocean. Comparison of Figures 2 and 3  shows variations of almost the same size emphasizing the difficulty of clearly identifying temperature trends resulting from greenhouse gas heating effects. 

Existing meteorological records have been questioned as the temperature records completeness and quality varies around the world. Records have been kept in the United States which are deemed to be the best in the world by some authors. Other experts[15] dismiss them as irrelevant because of the small land surface they represent. Figure 4[16] shows this United States data. No upward trend is evident to the naked eye. Data based on surface measurements has also been criticized as potentially biased since some of the data may be taken from close to cities which tend to heat their immediate surroundings. Comparisons with such data removed shows only a small effect[17] of about 0.1⁰C. 

Data from land based measurements leaves out a large fraction of the earth's surface which is covered by the oceans. Some researchers[18] have factored in measurements from sea based stations as well. The results are similar to those of Figure 2. In recent years data from satellites[19] has become available. Figure 5[20] shows temperature anomalies from a computed annual sinusoidal temperature cycle. The satellite measurements are from air higher in the atmosphere than the land based measurements. This explains the difference in magnitude of the observed anomalies. The authors identified no warming trend in the United States or global data presented in the paper. This is not surprising as the time period of ten years is very short.   Climatologists do not generally expect measurements of world climate to confirm or disprove modelling projections for one or two decades. The expected warming is too small to separate from normal fluctuations over a shorter time span. 

Recent scientific articles, based on results from computer modelling of the climate, are predicting temperature increases at the low end of the broad range of uncertainty (1.5⁰C to 4.5⁰C increase[21] for a doubling of carbon dioxide) in this science. Some of the differences in results arise from such simple changes in the models as a change from an assumed sudden doubling of carbon dioxide to a time linear increase of carbon dioxide to the same end point[22]. Other major uncertainties include those of cloud[23] and ocean circulation modelling. The nuclear industry has experienced similar modelling difficulties. Our simulations tend to be much simpler than simulations of the climate. We too encounter meagrely explained modelling phenomena such as differences between steady state and transient solutions[24] and unexplained asymmetry verified[25],[26] by test results.  

The data and modelling difficulties presented make it clear that it's really difficult to come to a clear conviction that the warming of the climate predicted by the greenhouse theory has been confirmed by measurement. In recent months these uncertainties in the modelling of climate have come to the attention of the popular press[27]. Projections of future temperature increases as detailed in Figure 6[28] are alleged by some experts[29] to be greatly in excess of what should really be expected. There are good, and irrational and emotional, arguments put forth from both sides of the debate. Considerable additional modelling and measurement research and/or more time is needed to establish the credibility of the models. We can expect that work intended to corroborate the existence of the greenhouse effect will be very interesting in coming years. 

GREENHOUSE RESEARCH DIRECTIONS? 

The scientists who are involved will continue with research and computer simulations. Public and political awareness of the issue will lead to substantial funding of research and our knowledge of the climate will increase.  A few more decades of prediction, measurement and validation of models will finally provide a basis for solid policy decisions on the issue. 

My literature review has identified some projects which seem particularly fruitful.  

A great deal of potentially useful information is being    extracted from ice taken from Antarctica and elsewhere. Some of this ice provides a 160,000 year record of atmospheric variables  from the air trapped in it. Data researchers have been able to obtain from it includes; carbon dioxide[30] and  methane[31] content, dust content[32], temperature and the time of deposition. 

Satellites are in use to track temperature as already discussed[33], ocean currents[34], plant life[35] and the greenhouse effect itself[36]. This last reference is particularly exciting as it measures the heat flux radiated from the upper atmosphere and compares this with the radiation expected from land and sea surfaces to get an estimate of the energy trapped by the atmosphere. These researchers also measured an amplified greenhouse effect associated with warm areas of the ocean. This is attributed to increased water vapour, another greenhouse gas, in the atmosphere above warm ocean water.

The expansion of low cost computing, which is essential to complex modelling, will be a boon to those who are involved in the prediction of climate change. 

Most of the validation work related to global circulation models tends to be based on naturally occurring global phenomena. So-called "separate effects" tests, of the sort the nuclear industry devises to validate codes, are rare in the climate change literature. Are there opportunities to devise closely controlled experiments to check out some aspects of the models? Ocean circulation is very important to the long term greenhouse effect. Is it well understood[37]? Could the effect of clouds and water vapour[38] be studied under controlled conditions to provide more reliable computer models? Perhaps the expertise the nuclear industry has developed in computer model validation could help provide answers to these and other questions. 

CONSERVATION AND ENERGY EFFICIENCY 

The nuclear industry is not the only group interested in the implications of the greenhouse effect on future energy supplies. The environmental groups who promote conservation and efficiency are convinced that the greenhouse effect can be avoided through implementation of their principles. They seem to believe that reduction of fossil fuel use through efficiency and conservation is clearly the most economic and desirable route to reduced greenhouse gas emissions and avoidance of global warming. 

There are two distinctly different ways of achieving conservation of energy. One way is simply to make do with less and use less. We could clearly conserve half of the energy we use in car transport by simply driving the small fuel efficient models which use half as much fuel. The other approach is to improve the efficiency of the car so it provides big car comfort and  performance while using less fuel. The environmental movement greatly favours the latter course of conservation via "efficiency abatement". Amory Lovins[39] of the Rocky Mountain Institute favours this approach as he believes, rightly no doubt, that it is more saleable to the consumer. He says President Carter failed in his conservation drive through rising energy prices. The record shows that fuel consumption did go down as a result of high gasoline prices which led to the development of more fuel efficient smaller cars. 

Efficiency enthusiasts assume that efficiency and/or conservation at the individual level will globally reduce carbon dioxide production. They also say it will save a lot of money while we're doing it. We can thus have our cake and eat it too. Amory Lovins has been quoted[40] as saying; "This is not a free lunch. This is a lunch you are paid to eat". 

Efficiency doesn't necessarily reduce fuel consumption. If we save money through efficiency we'll be able to spend more money on other energy consuming pursuits. This could take the form of new energy consuming appliances or perhaps additional travel or a bigger house. Economists point out that energy savings at the individual level of energy use do not automatically translate to savings at the macro-economic[41] level. A historical review reveals that the efficiency of energy applications has improved by an order of magnitude over the last century. Even as recently as 1920 thermal power plants were only about 10% efficient compared with 40% today, yet we now consume more energy per capita than we did a hundred years ago. 

The use of electricity is often castigated by the efficiency promoters because of the thermodynamic losses inherent in its generation. The energy benefits which may be recovered in its end use are often overlooked. Heat pumps are a major example. Electrical heating is more efficient than the wood or coal heat much of the world population is using for cooking. Furthermore, many production processes are amenable to greater efficiency through use of electricity. An overall trend to greater productivity per unit energy use and a reduction in total energy use is characteristic of countries which are tending toward greater[42] electricity use. 

It has not been conclusively demonstrated that efficiency improvements alone will lead to a lowering of carbon dioxide production. In fact, without the imposition of some hardship through higher taxes or naturally occurring shortages of fossil fuel it seems there is little reason to believe[43] conservation and efficiency of fossil fuel use will lead to reduction in global production of carbon dioxide.  

REQUIREMENTS OF THE NUCLEAR INDUSTRY 

The greenhouse effect has the potential to be the major  incentive over the next two or three centuries for reconsideration of nuclear energy as the major source of energy. Coal is the obvious alternative if the greenhouse effect turns out to be a minor hazard. Nuclear power plants, as they exist today, can be demonstrated, at least to the nuclear industry's satisfaction, to have minimal impact on the environment relative to fossil fuel derived energy. It is recognized by its friends and foes to produce very little carbon dioxide relative to most other means of energy production. 

Not everyone is convinced that nuclear energy is a solution to our energy needs. Some think the risks of nuclear power outweigh the benefits. Some argue that improvements in the efficiency of use[44] of fossil fuels are economically more attractive. Some purport to demonstrate that nuclear fuel supplies are too limited[45] to warrant a conversion to nuclear power of the scale needed to affect greenhouse gas production significantly. Recycling of nuclear fuel to extend the supplies is judged to be too risky. Dilute sources of nuclear fuel which the nuclear industry has cited [46],[47] are deemed to require too much energy to be worthwhile. A lot of the research undertaken by the environmental advocacy groups[48] is well presented and convincing to the layman. Most of the work concludes that nuclear energy is impractical, risky,  and uneconomic. 

In Canada the nuclear industry has already felt the benefits of public interest in the greenhouse effect. Recent Federal Government support for the industry rests, in part, on the intense interest in the greenhouse effect from the summer of 1988. Public interest has subsequently cooled considerably. The potential warming from the greenhouse effect will become just another plank in the long term case for nuclear power development. We can still expect that fossil fuel supplies will become more expensive and will have other adverse effects on the environment whereas nuclear power is relatively benign. The nuclear industry has been accused[49],[50] of not making a strong case for its benefits as an energy source.  A nuclear energy alternative to the carbon dioxide produced by fossil fuels will require enormous resources in materials to build reactors and substantial development of processes to extend nuclear fuel supplies and replace fossil fuels in transportation and manufacturing. The most difficult task of all will be to instill understanding and appreciation of past and possible achievements of the youthful and innovative nuclear power industry in the minds of the public and policy makers. The basis for fundamental understanding must come from the basic science and engineering principles we have established. We have a long difficult row to hoe to follow the lead of our visionaries[51] and establish the reality and practicality of the nuclear energy alternative to fossil fuels. It behooves us to have this in place if, and when, climatologists demonstrate that global warming is a reality to be reckoned with. 

CONCLUSIONS 

Nuclear fission derived electricity already makes a significant contribution to world energy supply. This proven technology is known to minimally contribute to the causes of the greenhouse effect relative to other means of energy use. More widespread adoption of the technology would thus be a prudent step to take while uncertainty with respect to climate change prevails. Nuclear fission has the potential to provide a far greater fraction of world energy needs. It's possible widespread adoption raises additional questions of environmental and economic concern. It is the responsibility of the nuclear industry to ensure balanced understanding of these concerns related to the risks and benefits of alternative energy sources in the minds of the public. The industry will then be in a strong position for consideration as a major source of energy should climate change turn out to be as serious as many believe.

REFERENCES

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