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The Tragedy Of The Commons -- Where Environmentalism SOMETIMES Makes Very Good Sense

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Karl Note: 

Most people who write about the tragedy of the commons have a strong anti-growth slant to their thinking.  Most of them turn out to be Anti-American, or at least Anti-Capitalist.  I, personally, Karl Loren, disagree with this prejudice.  The concept of "the commons" is, I think, quite valid, but the validity of any one area of "commons" depends on honest science.

The three articles below are influenced by and depend on Garrett Hardin, probably the most famous author to write on this subject.   He is a self-admitted enemy of the concept of morality in society.

Unfortunately he approached the subject with a strong bias toward restriction of uses of any resources, and he simply cloaked his personal morality (which included a strong advocacy for abortion) in the ancient and oft-quoted reference to "the commons," that resource which a group of people share "in common." 

Click here for more background on Dr. Garrett Hardin.

The three articles below are by Gary W. Harding, not Garrett Hardin, but they depend on the work done by Hardin.

Thus, it is clear that sheep eat grass down to the dirt, while cattle do not. When cattle graze on "common grazing land," the grass will continue to grow. When sheep graze on any land, the land will soon NOT be showing any grass at all. Thus, the common area of grass can be ruined by sheep grazing that has no control over it.  This is valid science.

Perhaps a new form of grass, or some other scientific break-through would allow sheep to graze without interruption?

But this valid example is not paralleled by the claim about "global warming."  This has not been established as "valid science."

I am not an authority on this, but I believe that "global cooling" is the more honest and accurate scientific assessment of our future climate -- and that is based on some simple facts that do not seem to be in dispute.

  • Plants and trees "breathe in" carbon dioxide and "breathe out" oxygen. This is one of the fundamental principles of continuing life on the planet.  Animals and humans breathe in oxygen and breathe out carbon dioxide.  Plants and trees breathe in carbon dioxide and breathe out oxygen.  There is a perfect balance here.
  • (At night plants take in oxygen and release carbon dioxide, but overall, during the entire day, the plant is always a net production unit for oxygen.)
  • Animals need certain foods to live, including plants.  Plants are, after all, the basic source of all food, even that eaten by animals that eat animals.  The ingredients needed to grow plants are not unknown.
  • Plants need carbon dioxide and soil that contains the nutrients needed by plants. The nutrients needed by plants and trees are well known, mostly, although the necessity for a broad range of trace minerals in the soil is not well appreciated.
  • If the soil contains all the necessary nutrients, as it did many thousands of years ago, then the ONLY restriction on the growth of plants and trees would be carbon dioxide.  The more carbon dioxide that would be put into the atmosphere, the more plants and trees would grow, releasing more and more oxygen. The perfect balance is there.
  • It is scientific fact that the atmosphere amount of carbon dioxide has increased appreciably over many decades.  Science finds that the amount of carbon dioxide in the atmosphere has increased about 25% since the start of the Industrial Revolution.
  • However, the actual percentage of carbon dioxide is very low -- about 0.3 %.
  • Thus we can conclude that plant growth (and production of oxygen) are NOT limited by a lack of carbon dioxide, but must be limited by the needed nutrients in the soil -- presumably the trace minerals.
  • Thus, the "danger" of higher levels of carbon dioxide may well be serious and real, but the cause is not being spotted accurately.
  • When you increase the amount of trace minerals in the soil, in fact the plants and trees will grow much faster and no amount of chemical fertilizer is either needed nor even better than "rock dust" spread over the soil.  This would be rock dust containing a mixture of the various trace minerals.
  • If the problem is related to the shortage of trace minerals in the soil? Yes? Where did they go?
  • As plants grow they absorb the trace minerals in the soil.  If all of the plant were allowed to live in one spot, and fall into decay, all of the components of that plant would, presumably, go back to revitalize the soil.
  • However, instead, we cut the plants and carry parts away for food.  In many places part of the plant is burned to make room for another crop.  Burning these plants releases the components, including trace minerals, as gases that escape into the atmosphere.
  • It also turns out that chemical fertilizers kill certain living organisms in the soil -- living organisms which convert inorganic minerals (rocks) into organic minerals which the plant can absorb and use for many different growth functions.
  • Pesticides and herbicides also kill these tiny living organisms in the soil -- the ones that allow the plant to absorb otherwise un-absorbable inorganic minerals.
  • So, our farming practices, based on chemical fertilizers, pesticides, herbicides, burning much of the plant mass, and finally carrying away the part of the plant needed for food --- these practices result in plants being starved for the trace minerals and therefore not capable of using the abundance of carbon dioxide that exists in the atmosphere.
  • What is nature's solution to this problem?
  • Another ice age!
  • The planet has had "ice ages" about every 100,000 years.  The ice creeps down from the north and glaciers grind over the rocks and mountains, creating rock dust. The rock dust is carried along by the glaciers and re-invigorates the soil.  The ice age and glaciers, at least in the past, have pushed all living animals (and humans) into a very small part of the earth, near the equator -- the only part of the planet warm enough to sustain life.
  • In the meantime the great bulk of the land mass is being "worked over" by glaciers and new floods, rivers, lakes and changes in the seas -- so the soil with no vegetation on it for many thousands of years, gets re-stocked with minerals -- now suitable for sustaining growth of trees and plants -- trees and plants that will grow and use the high amount of carbon dioxide in the atmosphere.
  • My information suggest that the ice age lasts about 90,000 years out of the 100,000 in each ice age cycle.
  • That means that the planet is habitable for about 10,000 years out of every 100,000 years.
  • This concept is obviously diametrically opposite to the "global warming" theory.
  • The point here is that the tragedy of the commons is a very valid concept, but it depends on valid science on the resources that are "common." 
  • If the common resource of "air," or the "atmosphere" is considered to be harmed by the burning of fossil fuel? And that burning of that fuel releases carbon dioxide (which it does) and this burning of these fuels is increasing the carbon dioxide percentage in the air?  (Which it may, even!), then global warming might a valid worry, for which the solution could seem to be to cut back on the use of carbon-based fuels, and that would mean a reduction in the consumption of energy, and a reduction in industrial activity -- exactly the argument of the global warming people.
  • But, if this increase in carbon dioxide in the atmosphere could be converted into more trees and plants (which is could)?  But, the lack of proper minerals in the soil prevents this? (Which it does!)   Then, why not just start putting minerals back into the soil -- which probably means great changes in the way we do our farming -- finding better alternatives for pesticides and herbicides, and use of rock dust instead of chemical fertilizer.
  • Once you start looking into these alternatives for farming you find that the lack of the trace minerals ALSO makes plants and trees more susceptible to insects and fire!  Plant diseases increase when the plants don't have enough of the trace minerals.  Trees actually catch fire (from lightening, etc.) much more easily when the tree hasn't had its ration of trace minerals.
  • (Humans also suffer the same problem -- from lack of trace minerals!)
  • So, the concept of "global cooling" would seem to be far more valid than "global warming," even though the global cooling concept would STILL call for enormous changes in "things the way they are!"

So, most of those who write about the "tragedy of the commons" are also claiming that we have a global warming trend that can ONLY be solved with reduced industrialization -- actually a reduction in the standard of living.

So, it is a valid moral rule that you should safeguard and protect the planet, but that does NOT mean that you should fight against the use of fossil fuels!

Related Links

General Description of "The Commons"

Why The Tragedy of the Commons is Not Always PopularGlobal Warming Trend -- More Tragedy

The Global Cooling Trend -- Valid In 1975, But Not Today

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The Commons

What is the Commons? The "commons" is any resource which is shared by a group of people. Such things as the air we breath and the water we drink come from commons. In many parts of the world; new land for farming and grazing land for stock, fish from the sea, and wood for fuel and housing are treated as commons. What is the Logic of the Commons?

The "logic of the commons" is as follows: Each household has the right to take resources from and put wastes into the commons. To accumulate wealth, each household believes that it can acquire one unit of resources or dump one unit of waste while distributing one unit of cost across all of the households with whom the commons is shared. Thereby, the gain to the household appears large and the cost very small. Some households accumulate wealth more rapidly than others and this, in turn, gives them the means to access an even larger share of the commons.

The fallacy in the logic of the commons lies in the failure to recognize that all households are attempting to do the same thing. Thus, on average, one unit of gain for a household actually produces a net one unit of cost for each household. However, selfish households accumulate wealth from the commons by acquiring more than their fair share of the resources and paying less than their fair share of the total costs. Ultimately, as population grows and greed runs rampant, the commons collapses and ends in "the tragedy of the commons" (Garrett Hardin, Science 162:1243, 1968). How does the Commons work? The logic of the commons breaks down when resources decline and/or population grows too large. Consider the following example: Fourteenth century Britain was organized as a loosely aligned collection of villages, each with a common pasture for villagers to graze horses, cattle and sheep. Each household attempted to gain wealth by putting as many animals on the commons as it could afford. As the village grew in size and more and more animals were placed on the commons, overgrazing ruined the pasture. No stock could be supported on the commons thereafter. As a consequence of population growth, greed, and the logic of the commons, village after village collapsed. An apparent solution to avert the collapse of the commons was the introduction of private ownership. Common lands were parceled up into small tracts, each owned by a household. If a household greedily destroyed its plot, its demise was its own fault. However, as population grew, each new generation of households was left with a smaller and smaller portion of the original holdings. And, there was still the opportunity for some households to accumulate wealth by acquiring land from others, one way or another. Thus, private ownership did nothing to control greed. It merely shifted to a new arena [See essay Politics, Economics and the Perpetuation of the Commons]. The number of landless households grew rapidly, each one descending deeper and deeper into abject poverty. Commons other than land were not so easily parceled up. How could anyone own rain, wind, and the open ocean? The logic of the commons still prevails today for: fishing rights in coastal waters; roads and highways for travel and commerce; and a standing military for defense of territory. The logic of the commons also includes a much more sinister element. As an example, consider the following episode: "After the Civil War, the cattlemen in Edwards County, Texas overstocked the land, and when settlers started showing up in the 1880s, the cattlemen's answer was to crowd even more animals onto the land. At a stockmen's meeting, they produced: 'Resolved that none of us know, or care to know, anything about grasses, native or otherwise, outside of the fact that for the present, there are lots of them, the best on record, and we are after getting the most of them while they last.' (D. Duncan, MILES FROM NOWHERE, Penguin Books, 1994, pg. 145)." Thus, we have cases of deliberate destruction of the commons to not only get the wealth out of it before someone else does, but also to leave nothing for others. Often, this has involved the ruin of other commons resources along with the ones sought after. The history of the quests for gold and whales are other examples. These kinds of episodes reflect instances of pure greed. The commons is an ancient cultural and economic organizing principle. Before the agricultural revolution, each clan or tribe staked out a territory and all members had the right to hunt and gather within it. They often did so cooperatively. This worked well as long as their territory could be held, the commons was vast, and the relative population was small. Before the agricultural revolution, a commons tragedy was rare. It usually involved declining resources due to natural events, such as ice-ages. The tragedy of the commons has become more and more frequent since the agricultural revolution and its concomitant population growth. Its frequency has accelerated with the industrial revolution and the resultant population explosion. Now, the commons includes the whole Earth. Why does the Commons continue? In addition to the obvious (land, water, and air), much of our world is still treated as a commons today. In many cases, resources from these commons are no longer free for the taking. Dumping our wastes into the commons is not as free as it once was. One must pay a fee or be licensed to get access to the commons. In some cases, how much one can take away or dump into the commons is managed and/or regulated. But, all around the world; fisheries, wood, national parks, highways, parking and many other resources are commons just the same. Access to them merely requires a desire to do so and sufficient means. Population growth, greed, and the logic of the commons has virtually destroyed the worlds ocean fisheries and the Amazon rain forest. Huge tracts of land have succumbed to desertification. Crowding overwhelms Yosemite National Park and the freeways and parking facilities in our big cities. The accumulation of greenhouse gasses in the atmosphere is precipitating significant global warming which will produce climate change [See essays The Atmospheric Commons and Global Warming and Human Population and Global Warming]. A significant loss of biodiversity is underway; some call it a mass-extinction event [See essay The Commons Unshared; Loss of Biodiversity].

Although international negotiations on managing the global commons for a sustainable yield continue, progress toward resolution is nil. Selfish points of view dominate the discussion [See essays Unpopular Science; The Tragedy Denied, We The People, and The Golden Rule]. Particularly intractable is control of population growth. The freedom to breed has been called "the second tragedy of the commons". Without population-growth control, greed and the logic of the commons makes a global-wide tragedy of the commons inevitable.

Copyright © 1995, 1996, 1997 by Gary W. Harding Last Updated 16 February 1997

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By Gary W. Harding We are all amazed, fascinated and even overwhelmed by the changes that scientific research has brought to our lives. All the advances have truly made our lives better. But, basic science seeks knowledge whether or not that information is beneficial. As a consequence, some scientific findings are unwelcome. Billions of people believe that, through science and technology, they can have it all and not have to pay the ultimate price. This belief is so strong that any evidence to the contrary is routinely rejected out of hand. And if ignoring the facts won't make those facts go away, a self-serving assault is mounted to discredit their validity. This phenomenon is apparent in the double-standard associated with society's acceptance of scientific knowledge. If scientific discovery produces benefits for people, the information is embraced. If, on the other hand, scientific inquiry suggests that there will likely be disastrous consequences from human activities, that news is very unpopular. Let me illustrate the science double-standard with two examples that we all are aware of: Awhile back, medical scientists hypothesized that it would be possible, under favorable circumstances, to transplant a heart from a recently deceased individual to replace a diseased one. They began studies to determine how to do it. At first, most scientists were skeptical of the results. Now, heart transplants are commonly done. About two decades ago, medical scientists hypothesized that cigarette smoking caused cancer. Later, second-hand cigarette smoke and smokeless tobacco were added to the hypothesis. Recently, scientists stated a connected hypothesis; nicotine is an addictive drug. Data were collected which clearly demonstrated that all this is true. The tobacco industry has fought the acceptance of these hypotheses with enormous investments in pseudoscience and political control. History Tells Us A turning away from science has happened before. About 800 years ago, conservative politics, fundamentalist religion, and a self centered focus rose to dominate societal views. This period lasted for nearly 400 years. The arts, sciences and education fell into disfavor. Those few who sought knowledge, despite the times, were labeled heretics. Many paid for their curiosity with their lives. This epoch in human history has been called "The Dark Ages". Today, we see the beginnings of another dark age. Conservative politics has taken over at the national and local level. Fundamentalist religion is gathering momentum. The people are becoming more and more self centered. Support for the arts is fading. Education has fallen into disfavor; most of our children can't read, write or calculate, let alone distinguish between truth and fiction. Among the people, a science-based understanding of the world we live in is being replaced with a self-serving system of conservative beliefs.

The Art of Science Scientists studying the mechanism of a natural phenomenon don't all agree on a proposed explanation (which they call an hypothesis). Questions are raised about how the data were collected, how accurate they are, and whether these data are valid measures of the hypothesis. For example, Newton's law of gravity started as an hypothesis which was scoffed at by other scientists. As much as they try to avoid it, a bias can creep in because a scientist didn't look at the right things or how the scientist looked was based upon a preconceived notion of what the answer should be. However, a consensus among scientists on an hypothesis develops as more and more data are collected. Consensus doesn't necessarily prove that an hypothesis is correct; history shows that some widely accepted hypotheses turned out to be wrong. However, most consensus-supported hypotheses turn out to be right. Nonetheless, although all are looking at the same data, there will always be a few scientists who disagree with an hypothesis. Pick and Choose Curiously, outside of the scientific community, the judgment from the scientific consensus prevails only when a popular hypothesis is advanced. However, if an hypothesis is unpopular, the contrary opinion of just one scientist is what gets all the attention. If this is not enough to make the hypothesis go away, a pseudoscience attack commences. Economic institutions who's profits are threatened by the hypothesis, contract for "independent" research. Their conclusion is, of course, always contrary to the offending hypothesis. Conservative interests use this pseudoscience to convince those in government to ignore the real science. They have even gone so far as to persuade legislative bodies to cut off funding for unpopular science. What verses Why If one separates scientific inquiry into measures of "what" is happening verses hypotheses of "why" it is occurring, we find that the vast majority of the differing opinions among scientists are about why and not about what. For example, measurements of atmospheric carbon dioxide concentration show that it has increased exponentially over the last five decades. It is now at a higher concentration than in all of human history. Prior scientific discovery showed that carbon dioxide concentration and mean global temperature go hand in hand through the greenhouse effect. Therefore, we expect global warming. This, if it goes too far, would be a climate-change threat to human survival. No scientist disputes the recent, reliably measured, carbon dioxide concentration data, although the historical data from ice cores may be somewhat less certain.

There is tremendous controversy, however, among scientists and non-scientists alike, about what these data portend. The scientific consensus is that global warming is real and it is bad news. It will get much worse if greenhouse gases emission rates are not slowed significantly. Economic interests translate this notion into reduced consumption, a prospect that they find threatening to profits. They have seized upon the opinion of the few scientific dissenters and pseudoscientific rhetoric to dismiss this unpopular science.

Perception Our position in space is changing at an phenomenal rate. The galaxy we live in is moving away from the big bang. The star which gives us life is spiraling at the edge of that galaxy. Our planet is revolving around that star and around its own axis. Yet, we perceive non of this motion. At the other end of the movement spectrum, the continent we live on is moving west at about 1 cm per year. The axis of the earth shifts orientation about a meter per year. It is not surprising that we do not perceive this because it is just too slow. But, we can measure these changes and verify that the motion is indeed occurring. We can measure other slow changes as well to verify that they are happening, although we cannot as yet perceive them. One of these changes that we can reliably measure is global temperature.

Global Warming

The International Panel on Climate Change (IPCC), a group of scientists drawing upon the data from thousands of scientists, has concluded that "... the balance of evidence suggests that there is a discernible human influence on global climate" (Richard A. Kerr; SCIENCE 270: 1565-1567, 1995). Mean global temperature has increased by about 1 degree centigrade since the beginning of the industrial revolution and will increase from 1 to 3.5 more degrees by the end of the next century. Although this does not seem like much, it is enough to precipitate major changes in global climate. Our descendants will curse us for not having done anything about it when we had the chance.

Last Updated 19 Dec 1995

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Global Warming


By Gary W. Harding In 1975, Wallace Broecker published a paper entitled: "Climate Change: Are We on the Brink of a Pronounced Global Warming?" (#1). The opening sentence of the abstract reads "If man-made dust is unimportant as a major cause of climate change, then a strong case can be made that the present cooling trend will, within a decade or so, give way to a pronounced warming induced by carbon dioxide." Broecker was not the first to draw this conclusion; Svante Arrhenius predicted in the late 1890s that a doubling of atmospheric carbon dioxide concentration ([CO2]) from its pre-industrial level would produce a 5o C world-wide increase in temperature (#2). But, Broecker was the first to analyze real data. His conclusion was based upon an astute assemblage of information from three sources. The first was an 800 year record of natural global-temperature cycles deduced from oxygen-isotope ratios (#3) in the ice core taken at Camp-Century, Greenland. The second was the direct measurements, which began in 1958, of [CO2 ] made at Mauna Loa Observatory, Hawaii. The third was the running average of global surface temperature assembled from world-wide meteorological data back to 1880.

Prior to the direct measurements, Broecker estimated past atmospheric [CO2] from fuel consumption data for 1900 through 1950. He projected future atmospheric [CO2] three decades beyond 1975 based upon the growth rate in the Mauna Loa data. Then he calculated the global temperature contribution expected from the past, present, and future [CO2]. The results were added to the natural temperature, Camp-Century cycles (CCC). This, in turn, he compared to the meteorological data on 1880 to 1975 mean global-surface air-temperature (MGST). The latter data were a compelling match. As a consequence of Broecker's paper, both scientific and popular debate ensued on the likelihood that future global warming was real and furthermore, how much there might be and whether significant warming was unavoidable. The controversy has continued to this day.

What makes Broecker's model so elegant is that it is relatively simple, yet captures the net essence of the processes involved in determining global temperature; all without having to simulate a myriad of details. To be sure, much more sophisticated climate-simulation models have been devised in the last 20 years. However, now that two decades have passed, Broecker's model warrants another look. Broecker's global temperature prediction was based upon the simultaneous warming effect of increasing [CO2] and the CCC. The Mauna Loa data on atmospheric [CO2] and the meteorological data on MGST over the two decades since 1975 have grown similarly to his predictions (see below; see also postscripts below). However, he stated: "As other anthropogenic effects are shown to be significant and as means to quantitatively predict their future influence on global temperature are developed, they can be included in models such as this." The data he used have continued to be collected and other effects, and ways to measure them, have been determined. Other greenhouse gasses, even with much smaller concentrations than CO2, have been shown to make significant contributions to global temperature (#4). Although extremely difficult to quantify, water vapor exerts a greenhouse effect as well. In addition, the cooling effect of aerosols (dust, smoke and sulfur compounds) has been documented (#5). Then, there is the cooling effect of clouds and the relation of cloud density to water vapor and aerosols (#6). To see if Broecker's model is nonetheless sound, it has been updated below to include these factors as well as what has been learned in the past two decades. The first question is; How well do the predictions from Broecker's original model match what has actually happened since it was published? To provide an answer to this question, the CCC, MGST, and [CO2] data have been updated as follows: 1) All data were entered in 5-year increments, rather than 10-years, starting in 1800. 2) The CCC have been extended to 2065 to see their implications well into the mid-twenty-first century (#7). 3) The five-year running averages of annual MGST from meteorological data have been extended up to 1990 (#8) with an additional estimate for 1995 based upon temperatures for 1993 and 1994 (#9).

4) The [CO2] estimates have been replaced for 1800 to 1955 with the data from air bubbles in the Siple ice core (#10, #11) and the Mauna Loa data have been extended for 1975-1990 (#10, #12). The calculation of the CO2 temperature contribution is the same as Broecker's; global temperature changes by 0.3o C for each 10% change in [CO2]. The [CO2] predictions have been extended at the current growth rate (3.2% / 5 yrs) until it doubles. (An alternative [CO2] scenario is discussed below.)

Figure 1. Updated data for Broecker's original graph. Upright triangles - Carbon dioxide temperature effect. Right triangles - Camp-Century natural temperature cycles. Circles - Net global temperature projection; sum of carbon dioxide effect and Camp-Century cycles. Squares - Mean global surface temperature from meteorological data.

The updated results for MGST (squares), CO2 effect (upright triangles), CCC (curve) and net effect (circles) have been plotted in Figure 1, similarly to Broecker's original figure. Although Broecker's graph of the predicted CO2 temperature effect out to 2010 appeared to grow exponentially, the one presented here is linear beyond that year. This is because the relation between [CO2] and temperature is logarithmic (#13). The update of Broecker's projection and MGST match well (r=.64), particularly up to 1975. However, they have deviated since then, with the actual MGST increasing more rapidly than he predicted. Assuming that the CCC closely reflect natural temperature cycles, the source of this deviation must lie in an underestimate of the greenhouse gasses temperature effect. To determine the magnitude of the underestimate, the CCC data were subtracted from the updated MGST data (Fig. 2; squares). These results represent an estimate of the net consequences from greenhouse-gas warming (including water vapor), aerosol and increased cloud-density cooling, and any as yet unknown factors which might be involved in global temperature. The divergence from Broecker's updated CO2-induced temperature forecast (Fig. 2; upright triangles) indicates that, since 1975, MGST has increased about twice as fast as he predicted. The next question is; If Broecker's prediction was an underestimate of net global warming, what would be a better one? To account for the discrepancy beyond 1975, the elements in his model have been modified as follows: 1) It has been estimated that CO2 accounts for less than half of the temperature effect due to all greenhouse gasses combined (#4). The atmospheric concentrations of methane and nitrous oxide, for example, are increasing even faster than that of CO2 (#14). Although their concentrations are much lower than that of CO2, methane, nitrous oxide and others are much more potent greenhouse gasses (#4). As global temperature increases, so does the amount of atmospheric water vapor. Therefore, the net temperature effect for all greenhouse gasses combined has been projected as double that for CO2 alone; the "carbon dioxide equivalent" (#15). Unlike Broecker's calculation, this projection extends seven decades into the future to 2065 when [CO2] at 567 ppm is double that in 1800 [280 ppm], prior to the rise of the industrial revolution.

Figure 2. Net warming effect from carbon dioxide and cooling effect from aerosols and clouds. Squares - Actual greenhouse gasses warming effect; mean global surface temperature minus Camp-Century cycles. Upright triangles - Updated projection of Broecker's carbon dioxide temperature effect. Diamonds - Estimated cooling effect; updated carbon dioxide temperature effect plus Camp-Century cycles minus mean global surface temperature. Inverted triangles - Fitted cooling curve based upon 50% of the updated carbon dioxide temperature effect.

2) The MGST data have been subtracted from the sum of the CCC data and updated net greenhouse-gas induced temperature data to produce an estimate of the cooling effect of aerosols and clouds (Fig. 2; diamonds). This, of course, assumes that Broecker's model is perfect, which it is not. It has been estimated that the magnitude of the this cooling effect is about half as big as the CO2 warming effect (#5). Thus, because the anthropogenic sources of aerosols are substantially the same as CO2 and volcanic sources are infrequent, the cooling estimate has been fitted with a curve calculated as 50% of the CO2 temperature effect (Fig. 2; inverted triangles). Here, it is assumed that the accumulation of aerosols in the atmosphere and increases in cloud density are directly proportional to CO2 accumulation, but the magnitude of the cooling effect is weaker than that of CO2-induced warming (#16). The two updated components of Broecker's original model (upright triangles and curve) and the added aerosol component (inverted triangles) are shown in Figure 3. When [CO2] has doubled, the predicted temperature effect from 1800, for all green house gasses combined, surpasses 4o C, about double that predicted by Broecker and many subsequent investigators (#15). The net change, however, is dependent on the other two factors. All three have been added together (circles) and plotted along with the updated MGST data (squares) in Figure 3 as well. Also, an horizontal dotted line has been placed at the maximum temperature in the last 850,000 years (#15). We reached this in 1990 and are heading, relative to the entire history of modern humans, into unknown territory. Revising the original two factors and including the cooling factor in Broecker's model produces an even closer match (r=.84) to MGST than before. The surprise is that, if greenhouse gas emissions continue at the present growth rate, the net change in MGST from 1990 will be more than 2o C a decade beyond mid-century. The growth in MGST will appear to slow between 2020 and 2050. However, this will be primarily due to the CCC and not to reductions in greenhouse-gas emissions, as will be apparent when growth in MGST accelerates thereafter. If, like Broecker's results twenty years ago, this prediction is an underestimate, the change in MGST would go even higher. On the other hand, suppose that this estimate is too high because anthropogenic greenhouse-gas emissions could be reduced over the next few decades. The developed nations have pledged to reduce these emissions, particularly CO2, to 1990 levels by the year 2000. If this were actually achieved world-wide for all sources by 2010, there would still be excess greenhouse gases accumulation, but at a linear rate (12 ppm / 5 yrs) rather than the current exponential growth. The net result would be a 0.45o C lower MGST in 2065, but [CO2] would still double by 2080.

Figure 3. Results from modified Broecker model. Upright triangles - Greenhouse gasses temperature effect. Inverted triangles - Fitted cooling curve from Fig. 2. Right triangles - Camp-Century natural temperature cycles. Circles - Net global temperature projection; sum of greenhouse gasses effect, cooling effect and Camp-Century cycles. Squares - Mean global surface temperature from meteorological data. Dashed lines - Fits to greenhouse gasses effect; one before 1950, the other after 2000. Dotted line - Maximum global temperature over last 850,000 years.

As compelling as the results from the updated Broecker model are, there are contrary views. The scientific criticisms of the model involve several questions, such as: 1) Are averaged meteorological data the best measure of global surface temperature? 2) Do the Camp-Century cycles represent natural fluctuations in global temperature? 3) Are the ice-core and carbon dioxide samples taken at a few sites representative of the whole earth? 4) Is the magnitude for the logarithmic relation between [CO2] and global temperature correct? 5) Do other measures of global temperature agree with the results from the model? 6) What exactly do we mean by "global temperature" in the first place? There are other data which are consistent with the model. The CCC match the estimates of temperature for Europe and North America reasonably well over the previous few centuries. The late-nineteenth through late-twentieth-century temperature data deduced from the Crete ice core (#15) is similar to the CCC and MGST data since 1880. However, the record for earlier times differs (see below). The record in rings from long-lived Japanese and California's bristlecone pine-trees (#15) agrees with the CCC. The temperature record deduced from sediment cores (#15) is similar to that from the ice cores. The data from North-American bore holes, which act as low-pass filters for daily and seasonal variations, indicate warming from the early to late 1800s up to present of about the same magnitude as that in MGST. These data show about a 1o C increase in mid-America and 2.5-4o C on the north slope of Alaska (#17). The CCC also appear as a component in the sun-spot cycles and there is a suspicion that these changes in solar output are the source of the CCC variations. Although the amplitude of the annual [CO2] cycle differs, the average concentrations at Barrow, Alaska; American Samoa; and the South Pole (measured since 1975) are nearly identical to that at Mauna Loa (#10). There are also data which are not consistent with the model in whole or in part. The temperature record from the Vostok ice core is based upon the concentrations of heavy hydrogen (deuterium) (#18). The overlapping part of this temperature time-series differs in part from the CCC. The temperature record from the Crete, Byrd, Siple, and GISP2 ice cores is also partially consistent and partially inconsistent with that of the core taken at Camp Century. The temperature above the global surface has been measured with balloons as long as [CO2] has been sampled at Mauna Loa. These data are similar to MGST from 1958 through 1975. However, little warming appears since 1980. In addition, satellite data which can be used to measure global temperature, have been collected since 1979. These results are very close to the overlapping part of the balloon data and show no warming, but this record begins just after a significant temperature increase in the balloon data in the late 1970s (#19). Also, the satellite time series is too short to draw reliable conclusions (#20). The balloon and satellite data, integrating over the lower 10 Km of the atmosphere, do not measure the same thing as MGST. Climatologists are interested in lower atmosphere and global surface temperatures in order to create models of climate and weather. People are, of course, interested in the impact of weather on their daily lives, but they are more affected by global-surface temperatures because that is where they make their living. As reflected heat is trapped low in the atmosphere, the boundary between the atmospheric layers may sink (#21). For example, if MGST increases by 2o C, temperatures could decrease by 10o C in the mesosphere (50-80 Km) and by 50o C above it in the thermosphere. Significant decreases in these temperatures and descending layer boundaries have been argued as yet another indicator of global warming. More disturbing, however, are the results shown by the dashed lines in Figure 3. Here, the projected greenhouse-gas temperature effect (upright triangles) has been fitted with two straight lines, one before 1950 and one after 2000. In feedback systems, a sudden change in slope like this is characteristic of a system-state change. A stable feedback system which is dominated by one factor, changes state rapidly when it is overtaken by another factor. Thomson (#22) has referred to this phenomenon as "capturing". If this is what has happened, Broecker's 1975 warning was already too late. There is circumstantial evidence that a state-change began to make itself apparent in about 1975. The most notable is the rise of a persistent El Nino since the mid-1970s (#15). The amplitude of the annual winter-summer temperature cycle is declining, primarily due to warmer winters (#22). Increases in Pacific Ocean temperatures off California have accelerated since 1976 and north-polar ocean temperatures have risen (#23). Indicators in the US lower 48 have shifted toward global warming (#24). More recently, a number of ecosystem anomalies have been documented: 1) An ocean-temperature-related record fish kill occurred off southern Australia (#25). 2) In the northern hemisphere, high latitude forests are showing signs of heat stress (#26). 3) Mean sea level is rising (#27); and many others. Another factor is that human population reached three billion in the mid-1950s. Assuming that the cause of the state-change is anthropogenic, this may have exceeded the maximum that the prior state of the ecosystem could sustainably carry at 1950s per capita resource consumption rates. In addition, if the ecosystem must accommodate a population of 12 billion people or more, as projected for the middle of the next century (#9), and at higher per capita consumption rates (#28), then this will add further forcing in ecosystem-state change. At the moment, we have no conclusive data as to exactly what precipitated this state-change. Either a major carbon sink saturated, or a former carbon sink flipped into a source, or both. The burning of fossil and wood fuels and the deforestation of large tracts of land are candidates for an explanation, but we cannot demonstrate a specific connection. As more data on the effects of aerosols and clouds are acquired, the simple cooling-estimate used here can be replaced with a more accurate accounting of this factor. But, the fact remains that greenhouse gasses will continue to dominate MGST unless their emissions are substantially curtailed.

The climate-change consequences of significant global warming are speculative and hotly (pardon the pun) debated. The lessons of the 1930s (#2), when the CCC and the greenhouse gasses warming effect reached a local maximum, and the results of climate-model simulations (e.g. #2, #5, #15 and #29) provide clues as to what might happen. However, there are points upon which there is general agreement (#2, #15): 1) High latitude temperatures will increase much more (2.5 - 4 times greater) than MGST; the "high latitude amplification effect". 2) Sea level will rise (thermal expansion and ice-melt), but not more than about one meter over the next few decades. Nonetheless, this will cause problems for low-lying coastal areas, particularly during storms. 3) Temperature is likely to be much higher and precipitation much lower in the center of continental masses than at their periphery. 4) The severity of storms will probably increase; producing stronger hurricanes, worse flooding, and wider annual temperature and precipitation extremes locally. 5) Moderate to severe drought in the Mid-West of the US is associated with every other sun-spot minimum (11 year cycles). The next one will occur in about 1997 (#2) along with a higher MGST than there has been since the last ice age. 6) The rapidity of the ecosystem state-change is at least an order of magnitude faster than any previous one that has been documented. 7) Thousands will most likely die every summer, as 4,768 did in the US alone during July and August 1936 and as 491 did in Chicago during the second week of July 1995, from the unrelenting heat. More speculative, however, are some extreme possibilities which indicate how serious this change in climate could be: 1) If a 5o C decrease in MGST from where we are now would put us in the depths of an ice age, we just don't know what a 5o C increase might do. 2) Five major mass extinctions over the last 440 million years of life on Earth have been documented. Some scientists (#30, #31) believe that the sixth one is in progress now, having started about 12,000 years ago. Although the causes of mass extinctions are controversial, each one has had a significant climate-change component. Unlike past mass-extinctions, however, this is the first one to have a strong animal-generated component (humans). 3) Increased MGST begets more increases because many positive feedbacks come into play. More water vapor produces more heat which generates more water vapor. As the Arctic tundra begins to thaw, more methane will be released from the thick layer of peat which in turn produces more thawing. Higher summertime temperatures increase the demand for air conditioning which increases the CO2 output of power plants. Population and per capita consumption growth increases the need for energy and agricultural land (thereby decreasing forests) which causes further releases of CO2. And so on. 4) What little is known about ecosystem dynamics already indicates that there are unknown effects out there. Relatively small changes in temperature can cross discontinuity thresholds and produce multiplicative synergistic effects which will present future surprises (#32; see also postscripts below). 5) The most frightening possibility is a global temperature runaway. This is what scientists believe happened to our sister planet Venus, although it involved a completely different mechanism than [CO2] regulation on Earth. Venus now has an atmosphere that is almost entirely CO2 and a small amount of water vapor and a global surface temperature of 315o C (#9). Can climate-change be averted? As noted above, even reducing greenhouse-gas emissions to 1990 levels world-wide will be far too little, far too late. Greenhouse-gas emissions would have to be reduced to 1950 levels immediately to eventually return to conditions prior to the state-change indicated in Figure 3. Thus, significant climate change can not be avoided without massive economic and political upheaval. The developed nations, with 20% of the world's population, consume 80% of the resources and produce 80% of the pollution, including greenhouse gasses (#33). The declining support for alternative energy research (#34) indicates that fossil fuels will continue to dominate for many decades. Neither is it likely that the wealthiest members of the population will voluntarily give up their standards of living. Population growth in developing nations, along with their desire for higher standards of living, is not likely to change significantly over the next few decades either (#35). Fossil fuels and forest clearance will predominate there even more so than in developed nations (#35). Computer simulations of human ecology (#36) indicate that a population crash is very likely in the next century. The prospects for halting the growth in MGST, or even slowing it down, and for avoiding a population and economic collapse do not look promising. Rather than coming together to face this unprecedented threat to all of us, the economic and political climate has turned hard to the right, focusing on short-term gain and ignoring the disastrous long-term costs and consequences.


In recent years, Wallace Broecker has argued that carbon dioxide induced global warming could eventually trigger a strong negative rather than positive feedback (SCIENTIFIC AMERICAN 273:62-68, 1995; SCIENCE 278:1582-1588, 1997). Man-made carbon dioxide (and other greenhouse gases) could upset the thermohaline circulation in the oceans. The result would be a substantial cooling component in northern hemisphere climate. Heat from the tropics would no longer be transported to the north which would produce a huge shift in climate in less than a decade. However, whether climate substantially warms over the next few decades or suddenly cools considerably, either would be catastrophic, particularly for agriculture.

In a letter to SCIENCE (Vol 283, 8 January 1999), Wallace Broecker has updated his original 1975 model by extending the data from 1975 through 1995. Although he did not substitute carbon dioxide equivalent for carbon dioxide (to account for all greenhouse gases combined) and did not add a component for aerosols and clouds (as was done here), his result is very similar to that presented above. However, Broecker doubts that the Camp Century cycles are a persistent feature of the natural-variation component of climate. Nonetheless, over the short term (as was done here), the Camp Century cycles likely predict the natural influence on climate over the next few decades.

References and Notes

1. W. S. Broecker, Science 189, 460 (1975). 2. H. W. Bernard, Jr., Global Warming Unchecked, Indiana University Press, Bloomington, IA (1993). 3. The Camp-Century cycles are an 80-year cycle and another with 180-year oscillations. 4. V. Ramanathan R.J. Cicerone, H.B. Singh and J.T. Kiehl, J. Geophys. Res. 90, 5547, (1985). 5. T. R. Karl, et al., in Aerosol Forcing of Climate, R. J. Charlson and J. Heintzenberg, Eds., pp. 363-382, John Wiley & Sons, Ltd., Chichester, U.K., (1995); R. A. Kerr. Science 268, 802 (1995); R. A. Kerr, Science 268, 1567 (1995). 6. J. T. Kiehl, Physics Today 47, 36 (1994); R. D. Cess, M. H. Zhang, P. Minnis, L. Corsetti, E. G. Dutton, B. W. Forgan, D. P. Garber, W. L. Gates, J. J. Hack, E. F. Harrison, X. Jing, J.T. Kiehl, C. N. Long, J. -J. Morcrette, G. L. Potter, V. Ramanathan, B. Subasilar, C. H. Whitlock, D. F. Young and Y. Zhou, Science 267, 496 (1995); V. Ramanathan, B. Subasilar, G. J. Zhang, W. Conant, R. D. Cess, J.T. Kiehl, H. Grassl and L. Shi, Science 267, 499 (1995); R. A. Kerr, Science 267, 454 (1995). 7. The Camp-Century cycles portend a natural warming trend through the two decades starting in 1990. This is followed by three decades of natural cooling and then significant warming again. 8. J. Hansen and H. Wilson, NASA Goddard Institute for Space Studies, "GISS Analysis of 1991 Global Surface Air Temperature" (Jan 6, 1992); P. D. Jones and T. M. L. Wigley, Sci. Am. 263, 84-91 (1995). 9. The World Almanac, Funk and Wagnells, Mahwah, NJ (1993, 1994). 10. W. M. Post, T.-H. Peng, W. R. Emanuel, A. W. King, V. H. Dale and D. L. DeAngelis, Am. Sci. 78, 310-326 (1990). 11. A. Neftel, E. Moore, H. Oeschger and B. Stauffer, Nature 315, 45-47 (1985); H. Friedli, H. Lotscher, H. Oeschger, U. Siegenthaler and B. Stauffer, Nature 324, 237-238 (1986); Broecker's estimated [CO2] values for 1900-1950 were within 1-4 ppm of these data. 12. K. W. Thoning, P. P. Tans and W. D. Komhyr, J. Geophys. Res. 94, 8549 (1989). 13. S. I. Rasool and S. H. Schneider, Science 173, 138 (1971). 14. R. J. Cicerone, Nature 334, 198 (1988); M. A. K. Khalil and R. A. Rasmussen, J. Geophys. Res. 97, 4651 (1992); A Kinzig and R. H. Socolow, Physics Today 47, 24 (1994). 15. J. R. Gribbin, Hot House Earth, Grove Weidenfeld, New York, NY (1990). 16. The interesting thing is that, between 1900 and 1975, the cooling effect is greater than this fitted curve, while the curve matches more closely as post-1975 clean-air regulations in Western Europe and North America have taken hold. 17. D. Deming, Science 268, 1576 (1995). 18. This core goes back more than 160,000 years. 19. R. A. Kerr, Science 267, 612 (1995). 20. R. W. Spencer and J. R. Christy, Science 247, 1558 (1990); P. D. Jones and T. M. L. Wigley, Nature 344, 711 (1990); J. R. Christy and R. T. McNider, Nature 367, 325 (1994). 21. R. G. Roble and R. E. Dickinson, Geophys. Res. Lett. 16,1441 (1989). 22. D. J. Thomson, Science 268, 59 (1995); R. A. Kerr, Science 268, 28 (1995). 23. D. K. Hill, Science 267, 1911 (1995); A. Regalado, Science 268, 1436 (1995); J. Travis, Science, 266, 1947 (1994). 24. T. R. Karl, R.W. Knight, D.R. Easterling, and R.G. Quayle, Consequences Spring, 3 (1995); R. A. Kerr, Science 268, 364 (1995). 25. G. O'Neill, Science 268, 1431 (1995). 26. G. Jacoby and R. D'Arrigo, Global Biogeochemical Cycles (1995).; G. Taubs, Science 267, 1595 (1995). 27. R. S. Nerem, Science 268, 708 (1995). 28. J. E. Cohen, Science 269,341 (1995). 29. C. D. Charles, D. Rind, J. Jouzel, R. D. Koster and R. G. Fairbanks, Science 269, 247 (1995). 30. P. Ward, The End of Evolution, Bantam Books, New York, NY (1994). 31. E. O. Wilson, The Diversity of Life, W. W. Norton, New York, NY (1992). 32. N. Meyers, Science 269, 358 (1995); J. T. Overpeck, Science 271, 1820 (1996) 33. The US alone, with 5% of the world's population, consumes 25% of the world's resources and produces 25% of the pollution. 34. Union of Concerned Scientists, The Global Warming Debate (1990). 35. J. Goldemberg, Science 269, 1058 (1995).

36. D. H. Meadows, D. L. Meadows and J. Randers, Beyond the Limits, Chelsia Green, Post Hills, VT (1992).


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