ARTICLES
The American public seems concerned with
the potential environmental impact of nuclear power, unaware of the "carbon problem".
As indicated by these articles, physicists are concerned with both. Politicians’ prime
concern often seems to be just getting elected, no matter what the present
or future environmental or security problems may be. The guiding premise
of our Forum has been that physicists have an obligation to help the
public force their politicians to deal effectively with these problems. They
can do so as individuals, via "non-partisan" educational groups
such as the Forum, or via issue- oriented "pressure groups" (such
as FAS, UCS, etc.) But they should be active!
The Science and Politics of Climate
Freeman J. Dyson
Talk given at American Physical Society Centennial Meeting
Atlanta, Georgia, March 25, 1999
Responding to the Joseph A. Burton Award Given by the APS
Forum on Physics and Society
Three agencies of the US government have
serious programs of climate research, NASA, NOAA and the Department of Energy.
I shall talk mostly about the Department of Energy because that is my home
territory. The Department of Energy program is the smallest of the three.
Anybody who had been primarily involved with the NASA or NOAA programs could
tell similar stories about them. My involvement began at the Oak Ridge National
Laboratory in 1972. Alvin Weinberg, who was director of Oak Ridge for many
years, started a program of climate studies there. He was running a major
nuclear power development program, with a large effort devoted to studying
the environmental and public health problems of nuclear power. He decided
to broaden the environmental studies to include effects of power-plants burning
fossil fuels. Weinberg is an interesting character in many ways. He is himself
a strong pro-nuke. He helped to build the first nuclear reactors at Oak Ridge
and spent most of his life promoting nuclear power. But he likes to listen
to opposing views. He collected at Oak Ridge a bunch of brilliant people,
including anti-nukes as well as pro-nukes, to study the environmental problems
associated with all kinds of energy. One of the anti-nukes at Oak Ridge was
Claire Nader, the sister of Ralph Nader. Weinberg liked her and always listened
to what she had to say. Allan Poole was another unusual character in the
group around Weinberg. Poole had been for some years a Buddhist monk in Thailand.
He was an expert on tropical forests. Another member of the group was Jack
Gibbons, who later became head of the Office of Technology Assessment and
science advisor to President Clinton.
The practical advice that Alvin Weinberg
gave to the Department of Energy was to increase the funding of field measurements,
physical measurements in the atmosphere and biological measurements on the
ground. The purpose of measurements in the atmosphere was to test the climate
models with real data. The purpose of measurements on the ground was to explore
the non- climatic effects of carbon dioxide on farms and forests. The department
did not pay much attention to his advice. The lion's share of the budget
for carbon dioxide research continued to be spent on computer models. The
amount of money spent on local observations is small, but the money has been
well spent.
Several successful programs of observation
have been started in recent years. One of them is a Department of Energy
program called ARM, Atmospheric Radiation Measurements. ARM's activities
are mainly concentrated at a single permanent site in Oklahoma, where systematic
observations of radiation fluxes in the atmosphere are made with instruments
on the ground and on airplanes flying at various altitudes. Measurements
are made all the year round in a variety of weather conditions. As a result,
we have a data-base of radiation fluxes as a function of wave-length, angle
and altitude, in clear sky and in cloud and between clouds. One of the most
important measurements is made by two airplanes flying one above the other
at different altitudes. Each airplane measures the fluxes of radiation coming
up from below and down from above. The difference measures the local absorption
of radiation by the atmosphere as a function of wave-length. The measured
absorption of sunlight turns out to be substantially larger than expected.
The expected absorption was derived partly from theory and partly from space-based
measurements. The discrepancy is still unexplained. If it turns out that
the anomalous absorption measured by ARM is real, this will mean that all
the global climate models are using wrong numbers for absorption.
The ARM program also has active sites in
the south-west Pacific and on the north shore of Alaska. The south-west Pacific
site made important contributions to the international TOGA program studying
El Nino. The south-west Pacific is the place where sea surface temperatures
are highest, and El Nino begins with a massive movement of hot surface water
from west to east. If we consider the global climate to be a heat-engine,
the south-west Pacific is the hot end of the engine and the north shore of
Alaska is the cold end. The ARM sites were chosen so that we can study the
hot and cold ends of the engine, with the Oklahoma site somewhere in the
middle. The original plan for ARM had two additional sites, one in tropical
forest and one in desert, but the funding for more sites never materialized.
Another successful program of local observation
is measuring directly the fluxes of carbon dioxide moving between the atmosphere
and the biosphere. This is done by putting instruments on towers above the
local trees or other vegetation. Accurate anemometers (wind-speed meters)
measure the vertical motion of the air, while infrared gas analyzers measure
the carbon dioxide content at the same place and the same time. Both measurements
are made instantaneously, four times a second, so that you are measuring
the carbon dioxide carried by each local eddy in the atmosphere as it moves
up or down. If, as usually happens in daytime in the summer, the trees are
absorbing carbon dioxide, each packet of air moving down carries more carbon
dioxide and each packet moving up carries less. You can derive the flux of
carbon dioxide going into the trees by multiplying the vertical speed by
the carbon dioxide abundance and averaging over time. This is called the
eddy covariance method of measuring fluxes. It is remarkably accurate, because
it turns out that the vertical speed and the carbon dioxide abundance are
almost a hundred percent correlated. When you measure at night or in winter,
you find that the flux is going the other way. Trees are then not photosynthesizing
but giving off carbon dioxide by respiration. The soil also gives off substantial
fluxes of carbon dioxide, mostly from respiration of microbes and fungi.
The eddy covariance method does not distinguish between vegetation and soil.
It measures the total flux leaving or entering the atmosphere.
For many years the eddy covariance measurements
were made in only three places in the world, one over a temperate forest
in Massachusetts, one over a tropical forest in Brazil, and one over a boreal
forest in Canada. Steven Wofsy at Harvard was the pioneer who got the whole
thing started at the site in Massachusetts, (Wofsy et al., 1993). The results
of the first measurements were startling. The Massachusetts forest was absorbing
carbon at a rate of 3.7 tons per hectare per year, far more than was expected
for a mature forest. If you supposed that all the temperate forests of the
world were absorbing carbon at this rate, the result would be an absorption
of 5 gigatons of carbon per year, which happens to be almost exactly the
amount of missing carbon that disappears from the atmosphere. The Amazon
forest shows an absorption of one ton per hectare per year, not so large
but still more than was expected, (Grace et al., 1995). The Canadian forest
is emitting carbon at a rate of 0.3 tons per hectare per year, probably mostly
from soil respiring more as the arctic climate grows warmer, (Goulden et
al., 1998). If these numbers are also representative of forests all over
the world, the tropical forests and the boreal forests roughly cancel each
other out, the tropical forests absorbing and the boreal forests emitting
about a gigaton each. The total for all forests would then be 5 gigatons
of absorption.
Finally, during the last few years, a serious
program of eddy covariance measurements has been started, with instrumented
sites in many countries around the world, to see whether the results observed
at the first three sites are really representative of forests in general.
A consortium called Ameriflux has been organized with 24 sites in north America,
and many other sites are operating in Europe and Asia. Results so far seem
to confirm the earlier measurements. One temperate forest site in Italy measures
5 tons per hectare per year absorption, and one boreal forest site in Sweden
measures half a ton per hectare emission. Within a few years, we will know
for sure whether the temperate forests are really the main sink of the missing
carbon. And the same technique of eddy covariance can be used to monitor
the carbon fluxes over agricultural croplands, wetlands and grasslands. It
will give us the knowledge required, so that we can use the tools of land
management intelligently to regulate the carbon in the atmosphere. Whether
we manage the land wisely or mismanage it foolishly, we shall at least know
what good or harm we are doing to the atmosphere.
Besides ARM and Ameriflux, there is a third
highly successful program of local measurements called ATOC, Acoustic Thermometry
of Ocean Climate, the brain-child of Walter Munk at the Scripps Institution
of Oceanography. ATOC uses low-frequency underwater sound to measure ocean
temperatures, (ATOC Consortium, 1998). A signal is transmitted from a source
on top of a seamount at a depth of 900 meters near San Francisco, and received
at six receivers in deep water around the north Pacific. The times of arrival
of signals at the receivers are accurately measured. Since the speed of propagation
depends on temperature, average temperatures of the water along the propagation
paths can be deduced. The main obstacle that Walter Munk had to overcome
to get the ATOC project started was the opposition of environmental activists.
This is a long and sad story which I don't have time to tell. The activists
decided that Munk was an evil character and that his acoustic transmissions
would endanger the whales in the ocean by interfering with their social communications.
They harassed him with lawsuits which delayed the project for several years.
Munk tried in vain to convince them that he also cares about the whales and
is determined not to do them any unintentional harm. In the end the project
was allowed to go forward, with less than half of the small budget spent
on monitoring the ocean and more than half spent on monitoring the whales.
No evidence was found that any whale ever paid any attention to the transmissions.
But the activists are continuing their opposition to the project and its
future is still in doubt.
During the two years that the ATOC system
has been operating, seasonal variations of temperature have been observed,
giving important new information about energy transport in the ocean. If
measurements are continued for ten years and extended to other oceans, it
should be possible to separate a steady increase of temperature due to global
warming from fluctuations due to processes like El Nino that vary from year
to year. Since the ocean is the major reservoir of heat for the entire climate
system, a measurement of ocean temperature is the most reliable indicator
of global warming. We may hope that the activists will one day admit that
an understanding of climatic change is as essential to the preservation of
wildlife as it is to the progress of science.
It is time now to wind up this talk and
summarize what we have learned. There is good news and bad news. The good
news is that we are at last putting serious effort and serious money into
local observations. Local observations are laborious and slow, but they are
essential if we are ever to have an accurate picture of climate. The bad
news is that the climate models on which so much effort is expended are unreliable.
The models are unreliable because they still use fudge-factors rather than
physics to represent processes occurring on scales smaller than the grid-size.
Besides the general prevalence of fudge-factors, the climate models have
other more specific defects that make them unreliable. First, with one exception,
they do not predict the existence of El Nino. Since El Nino is a major and
important feature of the observed climate, any model that fails to predict
it is clearly deficient. Second, the models fail to predict the marine stratus
clouds that often cover large areas of ocean. Marine stratus clouds have
a large effect on climate in the oceans and in coastal regions on their eastern
margins. Third, the climate models do not take into account the anomalous
absorption of radiation revealed by the ARM measurements. This is not a small
error. If the ARM measurements are correct, the error in the atmospheric
absorption of sunlight calculated by the climate models is about 28 watts
per square meter, averaged over the whole earth, day and night, summer and
winter. The entire effect of doubling the present abundance of carbon dioxide
is calculated to be about 4 watts per square meter. So the error in the models
is much larger than the global warming effect that the models are supposed
to predict. Until the ARM measurements were done, the error was not detected,
because it was compensated by fudge-factors that forced the models to agree
with the existing climate. Other equally large errors may still be hiding in
the models, concealed by other fudge-factors. Until the fudge-factors are
eliminated and the computer programs are solidly based on local observations
and on the laws of physics, we have no good reason to believe the predictions
of the models.
The bad news does not mean that climate
models are worthless. Syukuro Manabe, who ran the climate modeling program
at the Geophysical Fluid Dynamics Laboratory at Princeton, always used to
say that the purpose of his models was not to predict climate but to understand
it. Climate models are still, as Manabe said, essential tools for understanding
climate. They are not yet adequate tools for predicting climate. If we persevere
patiently with observing the real world and improving the models, the time
will come when we are able both to understand and to predict. Until then,
we must continue to warn the politicians and the public, don't believe the
numbers just because they come out of a supercomputer.
References:
ATOC Consortium, 1998. Ocean Climate Change: Comparison
of Acoustic Tomography, Satellite Altimetry and Modeling, Science, 281, 1327-1332.
Goulden, M. L. et al., 1998. Sensitivity of Boreal Forest
Carbon Balance to Soil Thaw, Science, 279, 214-217.
Grace, J. et al., 1995. Carbon Dioxide Uptake by an Undisturbed
Tropical Rain Forest in Southwest Amazonia, 1992 to 1993, Science, 270, 778-780.
Wofsy, S. C. et al., 1993. Net Exchange of $CO2$ in a Mid-Latitude
Forest, Science, 260, 1314-1417.
Freeman J. Dyson
Institute for Advanced Study, Princeton,
New Jersey
dyson@ias.edu
Nuclear Power and the Large Environment
David Bodansky
Talk given at American Physical Society
Centennial Meeting, Atlanta, Georgia, March 25, 1999
1. Introduction
The development of nuclear energy has come to a near halt
in the United States and in much of the rest of the world. The construction
of new U.S. reactors has ended and although there has been a rise in nuclear
electricity generation in the past decade, due to better performance of existing
reactors, a future decline appears inevitable as individual reactors reach
the end of their economically useful lives.
An obstacle to nuclear power is the publicly perceived
environmental risk. During this development hiatus, it is useful to step back
and take a look at nuclear-related risks in a broad perspective. For this purpose,
we categorize these risks as follows:
• Confined risks. These are risks that can be
quantitatively analyzed, and for which the likelihood and scale of possible
damage can be made relatively small.
• Open-ended risks. These are risks that cannot
be well quantified by present analyses, but which involve major
dangers on a global scale.
As discussed below, public concern has focussed on risks
in the confined category, particularly reactor safety and waste disposal. This
has diverted attention from more threatening, open-ended risks of nuclear weapons
proliferation, global climate change, and potential scarcity of energy in a
world of growing population. The rationale for this categorization and the
connection between nuclear power and these open-ended risks are discussed below.
2. Confined risks.
a. Nuclear reactor accidents.
The belief that reactor accident risks are small is based
on detailed analyses of reactor design and performance, and is supported by
the past safety record of nuclear reactors, excluding the accident at Chernobyl
in 1986. Defects in the design and operation of the Chernobyl reactor were
so egregious that the Chernobyl experience has virtually no implications for
present reactors outside the former Soviet Union. Chernobyl is a reminder,
however, of the need for careful, error-resistant design if there is to be
a large expansion of nuclear power in many countries.
At the end of 1998 there had been over 8000 reactor-years
of operation outside the former Soviet Union, including about 2350 in the United
States. Only one accident, that at Three Mile Island, has marred an otherwise
excellent safety record. Even at TMI, although the reactor core was severely
damaged, there was very little release of radioactivity to the environment
outside the reactor containment. Subsequently, U.S. reactors have been retrofitted
to achieve improved safety and, with improved equipment and greater attention
to careful procedures, their operation has become steadily more reliable.
A next generation of reactors can be even safer, either
through a series of relatively small evolutionary steps that build directly
upon past experience or through more radical changes that place greater reliance
on passive safety features--such as cooling water systems that are directly
triggered by pressure changes (not electrical signals) and that rely on gravity
(not pumps). It would in fact be remarkable if the accumulated past experience,
both good and bad, would not improve the next generation.
b. Nuclear waste disposal
The second dominant public concern is over nuclear wastes.
Current plans are to dispose of spent fuel directly, without reprocessing,
keeping it in solid form. Confinement of the spent fuel is predicated on its
small volume, the ruggedness of the planned containers, the slowness of water
movement to and from a site such as Yucca Mountain, and the continual decrease
in the inventory of radionuclides through radioactive decay.
Innumerable studies have been made to determine the degree
to which the radionuclides will remain confined. One way to judge the risks
is to examine these studies as well as independent reviews. An alternate perspective
on the scale of the problem can be gained by considering the protective standards
that have been proposed for Yucca Mountain.
Proposed standards were put forth in preliminary form
by the EPA in 1985. These set limits on the release of individual radionuclides
from the repository, such that the attributable total cancer fatalities over
10,000 years would total less than 1000. This target was thought to be achievable
when the only pathways considered for the movement of radionuclides from the
repository were by water. However, the development of the site was put in jeopardy
when it was later recognized that escaping 14C could reach the "accessible environment" relatively
quickly in the form of gaseous carbon dioxide. A release over several centuries
of the entire 14C inventory at Yucca Mountain would increase the worldwide atmospheric
concentration of 14C by about 0.1%, corresponding to an annual average dose of about
0.001 mrem per year for hundreds of years. The resulting collective dose to
10 billion people could be sufficient to lead to more than 1000 calculated
deaths.
It is startling that 14C might have been the show-stopper for Yucca
Mountain. It appeared that this could occur, until Congress took the authority
to set Yucca Mountain standards away from the EPA pending future recommendations
from a panel to be established by the National Academy of Sciences (NAS).
The panel issued its Report in 1995. It recommended that the
period of concern extend to up to one million years and that the key criterion
be the average risk to members of a "critical group" (probably numbering
less than 100), representing the individuals at highest risk from potentially
contaminated drinking water. It was recommended that the calculated average
risk of fatal cancer be limited to 10-6 or 10-5 per
person per year. According to the estimates now used by federal agencies
to relate dose to risk, this range corresponds to between 2 mrem/year and
20 mrem/year.
Taking the NAS panel recommendations into consideration,
but not fully accepting them, the EPA in August 1999 proposed a standard whose
essential stipulation is that for the next 10,000 years the dose to the maximally exposed
future individual is not to exceed 15 mrem per year. This may be compared to
the dose of roughly 300 mrem per year now received by the average person
in the United States from natural radiation, including indoor radon.
Attention to future dangers at the levels represented
by any of these three standards can be contrasted to our neglect of much more
serious future problems, to say nothing of the manner in which we accept larger
tolls today from accidents, pollution, and violent natural events. While we
have responsibilities to future generations, the focus should be on avoiding
potential disasters, not on guarding people thousands of years hence from insults
that are small compared to those that are routine today.
c. Fuel cycle risks
Risks from accidents in the remainder of the fuel cycle,
which includes mining, fuel production and waste transportation have not attracted
as much attention as those for reactor accidents and waste disposal, in part
because they manifestly fall into the confined-risk category. Thus, the September
1999 accident at the Tokaimura fuel preparation facility resulted in the exposure
of many of the workers, including two cases of possibly fatal exposures. It
involved an inexcusable level of ignorance and carelessness and may prove a
serious setback to nuclear power in Japan and elsewhere. However, the effects
were at a level of harm that is otherwise barely noticed in a world that is
accustomed to coal mine accidents, oil rig accidents, and gas explosions. The
degree of attention given the accident is a measure of the uniquely strict
demands placed on the nuclear industry.
3. Open-ended risks
a. Nuclear weapons proliferation.
The first of the open-ended risks to be considered is
that of nuclear weapons proliferation. A commercial nuclear power program might
increase this threat in two ways:
- A country that opts for nuclear weapons will have a head start if it has
the people, facilities, and equipment gained from using nuclear power to
generate electricity. This concern can explain the U.S. opposition to Russian
efforts to help Iran build two nuclear power reactors.
- A terrorist group might attempt the theft of plutonium from the civilian
fuel cycle. Without reprocessing, however, the spent fuel is so highly radioactive
that it would be very difficult for any sub-national group to extract the
plutonium even if the theft could be accomplished.
To date, the potential case of Iran aside, commercial
nuclear power has played little if any role in nuclear weapons proliferation.
The long-recognized nuclear weapons states---the United States, the Soviet
Union, the United Kingdom, France, and China---each had nuclear weapons before
they had electricity from nuclear power. India's weapons program was initially
based on plutonium from research reactors and Pakistan's on enriched uranium.
The three other countries that currently have nuclear weapons, or are most
suspected of recently attempting to gain them, have no civilian nuclear power
whatsoever: Israel, Iraq, and North Korea.
On the other side of the coin, the threat of future wars
may be diminished if the world is less critically dependent on oil. Competition
over oil resources was an important factor in Japan's entry into World War
II and in the U.S. military response to Iraq’s invasion of Kuwait. Nuclear
energy can contribute to reducing the urgency of such competition, albeit without
eliminating it. A more direct hope lies in stringent control and monitoring
of nuclear programs, such as attempted by the International Atomic Energy Agency.
The United States' voice in the planning of future reactors and fuel cycles
and in the shaping of the international nuclear regulatory regime is likely
to be stronger if the United States remains a leading player in the development
of civilian nuclear power.
In any event, the relinquishment of nuclear power by the
United States would not inhibit potential proliferation unless we succeeded
in stimulating a broad international taboo against all things nuclear. A comprehensive
nuclear taboo is highly unlikely, given the heavy dependence of France, Japan,
and others on nuclear power, the importance of radionuclides in medical procedures,
and the wide diffusion of nuclear knowledge —— to say nothing of
the unwillingness of the nuclear weapons states to abandon their own nuclear
weapons.
b. Global climate change.
The prospect of global climate change arises largely from
the increase in the atmospheric concentration of carbon dioxide that is caused
by the combustion of fossil fuels. While the extent of the eventual damage
is in dispute, there are authoritative predictions of adverse effects impacting
many millions of people due to changes in temperature, rainfall, and sea level.
Most governments profess to take these dangers seriously, as do most atmospheric
scientists. Under the Kyoto agreements, the United States committed itself
to bring carbon dioxide emissions in the year 2010 to a level that is 7% lower
than the 1990 level. Given the 11% increase from 1990 to 1997, this will be
a very difficult target to achieve.
Nuclear power is not the only means for reducing CO2 emissions.
Conservation can reduce energy use, and renewable energy or fusion could in
principle replace fossil fuels. However, the practicality of the necessary
enormous expansion of the most promising forms of renewable energy, namely
wind and photovoltaic power, has not been firmly established. Additionally,
we cannot anticipate the full range of resulting impacts. Fusion is even more
speculative, as is the possibility of large-scale carbon sequestration. If
restraining the growth of CO2 in the atmosphere warrants a high
priority, it important to take advantage of the contribution that nuclear power
can make---a contribution clearly illustrated by French reliance upon nuclear
power.
c. Global population growth and energy limits.
The third of the open-ended risks to be considered is
the problem of providing sufficient energy for a world population that is growing
in numbers and in economic aspirations. The world population was 2.5 billion
in 1950, has risen to about 6 billion in 1999, and seems headed to some 10
billion in the next century. This growth will progress in the face of eventual
shortages of oil, later of gas, and still later of coal.
The broad problem of resource limitations and rising population
is sometimes couched in terms of the "carrying capacity" of the Earth or, alternatively,
as the question posed by the title of the 1995 book by Joel Cohen, How Many
People Can the Earth Support? As summarized in a broad review by Cohen,
recent estimates of this number range from under 2 billion to well over 20
billion, centering around a value of 10 billion.
The limits on world population include material constraints
as well as constraints based on ecological, aesthetic or philosophical considerations.
Perhaps because they are the easiest to put in "objective terms," most
of the stated rationales for a given carrying capacity are based on material
constraints, especially on food supply which in turn depends upon arable land
area, energy, and water.
Carrying capacity estimates made directly in terms
of energy, in papers by David Pimentel et al. and by Gretchen Daily et
al., are particularly interesting in the present context as illustrations
of the possible implications of a restricted energy supply. Each group concludes
that an acceptable sustainable long-term limit to global population is under
2 billion, a much lower limit than given in most other estimates. They both
envisage a world in which solar energy is the only sustainable energy source.
For example, in the Pimentel paper the authors conclude that a maximum of 35
quad of primary solar energy could be captured each year in the United States
which, at one-half the present average per capita U.S. energy consumption rate,
would suffice for a population of 200 million. For the world as a whole, the
total available energy would be about 200 quads, which Pimentel et al. conclude
means that "1 to 2 billion people could be supported living in relative prosperity."
One can quarrel with the details of this argument, including
the maximum assumed for solar power, but it dramatically illustrates the magnitude
of the stakes, and the centrality of energy considerations.
4. Conclusions.
If a serious discussion of the role of nuclear power in
the nation's and world's energy future is to resume, it should focus on the
crucial issues. Of course, it is important to maintain the excellent safety
record of nuclear reactors, to avoid further Tokaimuras, and to develop secure
nuclear waste repositories. But here --considering probabilities and magnitudes
together -- the dangers are of a considerably smaller magnitude than those
from nuclear weapons, from climate change, and from a mismatch between world
population and energy supply.
The most dramatic of the dangers are those from nuclear
weapons. However, as discussed above, the implications for nuclear power are
ambiguous. For the other major areas, the picture is much clearer. Nuclear
power can help to lessen the severity of predicted climate changes and can
help ease the energy pressures that will arise as fossil fuel supplies shrink
and world population grows. Given the seriousness of the possible consequences
of a failure to address these matters effectively, it is an imprudent gamble
to let nuclear power atrophy in the hopes that conservation and renewable energy,
supplemented perhaps by fusion, will suffice.
It is therefore important to strengthen the foundations
upon which a nuclear expansion can be based, so that the expansion can proceed
in an orderly manner — if and when it is recognized as necessary. Towards
this end, the federal government should increase support for academic and industrial
research on nuclear reactors and on the nuclear fuel cycle, adopt reasonable
standards for waste disposal at Yucca Mountain, and encourage the construction
of prototypes of the next generation of reactors for use here and abroad. Little
of this can be done without a change in public attitudes towards nuclear power.
Such a change might be forcibly stimulated by a crisis in energy supply. It
could also occur if a maverick environmental movement were to take hold, driven
by the conclusion that the risks of using nuclear power are less than those
of trying to get by without it.
David Bodansky
Department of Physics, Box 351560
University of Washington
Seattle, WA 98195
bodansky@phys.washington.edu
1. Joel E. Cohen, How Many People Can the Earth Support?
(W.W. Norton & Co, New York, 1995).
2. David Pimentel et al, "Natural Resources and Optimum Human
Population," Population and the Environment, A Journal of
Interdisciplinary Studies 15, no. 5 (May 1994), 347-69.
3. Gretchen C. Daily, Ann H. Ehrlich and Paul R. Ehrlich, "Optimum
Human Population Size," Population and the Environment, A
Journal of Interdisciplinary Studies 15, no. 6 (July 1994),
469-475.
