Edwin Wilsey '04 Professor Emeritus
Department of Mechanical and Aerospace Engineering
School of Engineering and Applied Science
Princeton University, Princeton, NJ 08544
Most people have now heard of global warming. Most have been told that fossil fuels emission of green house gases, carbon dioxide in particular, is affecting the climate, and that if nothing is done about it, then over the next century or two the average temperature of the globe may rise by 6 to 11 degrees Fahrenheit (NY Times editorial, Oct. 28th, 2000), sea level may rise by several feet, and many additional undesirable events---such as floods, droughts and storms---may become more frequent and intense. Assuming that these dire warnings are credible, what should we do about this impending crisis? All seem to agree that we must reduce fossil fuels emission of green house gases, carbon dioxide in particular. Many suggest that we should try to increase the efficiency of our use of fossil fuels, encourage the use of renewable energy, and even to directly sequester carbon dioxide under deep oceans. Some websites advise citizens to develop good energy conservation habits to help fight global warming. Do we know what we are doing? Have we considered all the options? What if this is a false alarm? What if this crisis is for real?
Before the middle of the 19th century, our use of fossil fuels (mainly coal) played a negligible role in the carbon cycle of the earth. The natural sources and sinks of atmospheric carbon (in the form of carbon dioxide) were in approximate equilibrium. The pre-industrial amount of carbon dioxide in the atmosphere was constant at approximately 600 GtC (or its concentration was 280 ppmv) for a long time. Since then, our appetite for energy has grown enormously, and we have been busy digging and pumping coal, oil and gas out of the ground, burning them, and releasing carbon dioxide to the atmosphere. Such fossil fuels emissionsrepresent the main bulk of anthropogenic(done by humans) emissions,and the total accumulated amount emitted from 1840 to 1990 is approximately 220 GtC. A significant fraction of this accumulated emission was absorbed by the natural sinks, while approximately 150 GtC stayed in the atmosphere, bringing the current amount in the atmosphere to 750 GtC (or 350 ppmv). The average global temperature has arisen about one degree Fahrenheit in this period. If this temperature rise is attributed totally to atmospheric carbon dioxide, then empirically each 100 GtC increase had warmed the globe by about half a degree Fahrenheit. In 1994, the annual global fossil fuels carbon dioxide emission rate was approximately 6 GtC per year, and the rate of increase of atmospheric carbon dioxide was approximately 3 GtC per year. Both of these numbers are rising with time.
How much below is substantially below? To get quantitative answer to this question, one needs to go to page 25 of the 1995 IPCC report and study the data presented in Fig. 7(a,b). Reading numbers off the graph, we find that the long term global emission rates for the three stabilized cases mentioned previously are approximately 80%, 70% and 60% below the 1994 emission rate, respectively. If we arbitrarily set doubling of the pre-industrial concentration as our stabilization target, then the long term allowable global emission rate is about 1.5 GtC per year (by interpolation of the data)---approximately 75% below the 1994 value. Since the per capita energy consumption rate (particularly in the developing countries) and the world's population are both expected to increase significantly in the future, this 1.5 GtC per year global emission rate is not only substantially below the 1994 value, but is very, very, verysubstantially below the value expected in any business-as-usual fossil fuels-oriented world. What happens if we make a valiant effort but only succeed in reducing the emission rate to 3 GtC per year starting immediately? The IPCC data predict the atmospheric carbon dioxide concentration would triple after about three centuries.
Based on the above exposition, it would be fair to say that the Summary for Policymakerson page 3 of the 1995 IPCC report did not fully convey to the public the monumental magnitude of the task (of atmospheric carbon dioxide stabilization) confronting us, our children, our grandchildren and their children and grandchildren, etc. The graphs presented on page 25 of the same report deserve much more attention than they were given by the report. We cannot allow the future energy needs of our grandchildren to depend completely on Fig. 7(a,b) being wrong (in our favor) by a factor larger than four or five.
The public consciousness of the magnitude of the problem must be raised. The opinion molders in the media and our policymakers should be encouraged to read beyond page 3 of the 1995 IPCC report---certainly page 25 should be mandatory reading. Advocates of specific policy options should be prepared to answer the following questions:
A realistic projection of fossil fuels usage is that it will increase for the rest of the 21st century, and peaking and falling off there after because explorations will become increasingly difficult. Many believe that the total reserve of fossil fuels on earth could be exhausted about five centuries from now. A most important question is: What do we do five centuries from now? This simple question deserves an answer whether one believes in global warming or not.
Why don't more people think and talk about the future of our globe in the millennium time scale? How would you feel toward Galileo if he had discovered oil and gas in the 16th century, taught the world to take full advantage of the abundance and built a wealthy and prosperous world, while he knew all the time that in so doing all of the world's fossil fuels endowment (including coal) would be spent by the time we come along?
What about nuclear energy (fission using breeder technology)? It generates no greenhouse gases, is essentially inexhaustible, and is economically competitive with current technology. It has very satisfactory answers to the two bulleted questions posed above.
Fission nuclear energy has been in most people's dog house for a long time, particularly after Three Mile Island and Chernobyl. At the present time, the nuclear option is not politically correct. It is frequently briefly mentioned and then quickly discarded without comments in the global warming literature. There are three major objections to nuclear energy:
It is clear that the nuclear option can serve as a benchmark for us as we assess all the options on the table. Compare the degree of difficulty between asking the fossil fuels-oriented world to very severely reduce fossil fuels carbon dioxide emissions versus asking the best and the brightest modern nuclear engineers to come up with a new design of (hi-tech) nuclear reactors which convincingly address these objections.The world that successfully adopts the nuclear option can continue to enjoy energy abundance.
We have time. It is unlikely that the severity of the worst case scenario of global warming is going to be unbearable in the next fifty years. If we start working seriously on nuclear energy soon, it is entirely possible that in fifty years we shall have very satisfactory rebuttals to all three objections listed above (perhaps fusion is then also on the table). Once we can count on nuclear energy as the backbone of our energy supply (generating electricity and producing clean chemical fuels such as hydrogen), the global warming crisis is no more. If the global warming crisis is in fact a false alarm, it can still claim credit for prompting us to think about our great, ... , great grandchildren who will be living on this beautiful globe five hundred years or more in the future.
We must seriously talk and debate the---clearly
politically incorrect----nuclear option.