Policy Options for Global Warming

 S. H. Lam
lam@princeton.edu

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?

Some Non-controversial Facts from the Past and Present
    The total amount of carbon dioxide in the atmosphere is commonly expressed in terms of either GtC (gigatons or billions of tons of carbon) or ppmv (parts per million by volume). The conversion factor between these two units is 2.13---one ppmv equals 2.13 GtC. In what follows, we shall round off all numbers to simplify the exposition.

    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.

Predicting the Long Term Future
    All of the above numbers came from actual measurements; none came from computer models. In order to make statements about the future, however, theories and computer models are needed. The Intergovernmental Panel on Climate Change (IPCC), established in 1988 by the World Meteorological Organization andthe United Nations Environmental Programme,issued a 572 page report (The Science of Climate Change) in 1995 which included the results of many computer models. In its Summary for Policymakerson page 3, the following two bullets are of particular interest here: The first bullet says immediately holding the global anthropogenic carbon dioxide emission rate forever constant at the 1994 level is not good enough. The second bullet says if it is desired to "stabilize''  the atmospheric carbon dioxide concentration  ( i.e. holdingits value constant forever)  at some level higher than today, the global anthropogenic carbon dioxide emission rate in the long term (century scale) must be substantially belowthe 1994 value.

In the draft version of the 2001 IPCC Summary for Policy Makers (approved at 6th session of WG III, 2/28-3/3/2001, Accra, Ghana), its article 9 says "To achieve stabilization ... a very significant reduction in world carbon emission per unit of GDP from 1990 levels will be necessary." Again, as was the case in the 1995 report, it DID NOT say quantitatively what is meant by "very significant reduction."
    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.
When a system is "stabilized" or in "steady state," it means the rate things are coming in equals the rate they are going out. For example, in a stabilized or steady state university, the size of its graduation class is approximately equal to the size of its freshman class. It is easy to show that its total student population is given apprximately by (the size of the freshman class) times (the residence time of the students). Thus, if the goal of a four year university is to have a total studnet population of 4000, the freshman class size is approximately 1000. The same mathematics applies to the carbon dioxide cycle---the amount in the atmosphere above the pre-industrial level is the total student population, and the annual emission rate is the freshman class size. The computer simulations in the IPCC reports essentially say that the residence time of carbon dioxide in the atmosphere is approximately 400 years. More recent IPCC simulations also yielded the same order of magnitude for this resident time (see the graphs on page 23 of the most recent simulation data in http://www.ipcc.ch/pub/IPCCTP.III(E).pdf). Why is the computed life time so long? In these models, the CO2 "graduates" (thus leaving the 'campus' of our environment) only when it slowly makes its way to the bottom of the ocean. However, there exists no credible observational data to validate the model or the numerical parameters used in this part of the 'predictions.'

    In spite of the best efforts by the modeling scientists, all such long term predictions necessarily contain assumptions which are nearly impossible to validate. Hence all the numbers discussed immediately above may have large errors. But even if these numbers are off by a factor of two or three, it is clear that the per capita fossil fuels consumption rate for the next few centuries must be held to a very small fraction of the 1994 value (probably less than one quarter) in order to stabilize atmospheric carbon dioxide concentration at approximately twice the pre-industrial level.

    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.

Assessing the Policy Options
    In view of the above (the readers are welcome to study the IPCC reports and other research papers to verify that the consensus estimate of the residence time of atmospheric carbon dioxide is of the order of 400 years), do any of the proposals being currently discussed make any sense? What could the Kyoto Protocol do for us? What would be the impact of a 30% more efficient internal combustion engine? What would be the impact of two more Three Gorges Dams? How big a role can wind and solar power play under the best circumstances? How many gigatons of carbon dioxide need to be sequestered per year to make a measurable impact? Remember, these valiant efforts make sense only if the total global emission rate could be reduce to one quarter of the 1994 value or less. Unless the numbers add up, the rationalization that every little bit helps just doesn't wash here---they are then merely delaying tactics.

    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:

The uninformed may be impressed by assertions such as "... this option will reduce carbon dioxide emission by one billion tons per year ...," but the informed readers should know immediately that it is not nearly enough; they should ask the second question and demand answers. The Kyoto Protocol calls for a 5-7% reduction below the 1990 emission rate by the end of this decade, and its public discourse so far has avoided the second question. It is imperative to make sure that our policymakers do not assume that the answer to the second question is "yes, this will take care of it", or "no, but just a tiny bit more will finish the job." The obvious virtues of increased efficiency in our use of energy, a stronger role for renewable energy sources, direct carbon dioxide sequestration, etc. are notin dispute. Research must continue. However, it is highly unlikely that the sum of all these efforts together can provide a satisfactory answer to the the second bulleted question posed above---unless we unilaterally and very severely (by more than 50%, optimistically speaking) curb the energy appetite of our future generations.

    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:

The first two objections are technical in nature: the current nuclear power plants are not safe enough, and the current disposal of radioactive waste is not leak-proof enough. But there have been spectacular advances in technology since Three Mile Islandand Chernobylreactors were built, particularly in materials and sensors and the technology of intelligent machines which exploits the enormous programmable computing power of the modern microprocessor.  The third objection is not technical in nature, but it is entirely possible that advanced modern technology could also provide solutions.

    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.