|Is Global Warming A Real Problem?
(And if it is, what can be done about it?)
Stan Robertson, Ph.D.
Possible anthropogenic contributions to global warming have been the subject of recent debates, discussions and much media interest. At the extremes, many believe that we are at the threshold of a man-made environmental disaster, while others believe that the apparent warming of earth by about one degree Fahrenheit in the past 150 years has little or nothing to do with human activity. Ideally the conflicting views would be sorted out by scientists collecting and weighing evidence which policy makers would use as guides to actions intended to deal with any threats to environment or society. Part of this process has already taken place. The Intergovernmental Panel on Climate Change (IPCC, see http://www.ipcc.ch/) has issued a series of reports that place increasing emphasis on (a) the reality of global warming and (b) the need
for world governments to take actions to reduce the threat to the environment.
This message has received strong reinforcement from both broadcast and print media. The movie "An Inconvenient Truth", by former U.S. Vice President Al Gore has been very successful in creating both alarm and a sense of urgency for taking action. The claim is made in the movie and by many in the media, that the evidence is in, the debate is over and there is no credible scientific support for opposing views. This claim is probably premature because we have only arrived at the point of public awareness of a potential problem. The next step will require convincing the public of the validity of the evidence and the effectiveness of any proposed remedies. This may not be easy. A March 14, 2007 Oxford-style debate in New York City, sponsored by the Rosenkranz Foundation, and moderated by Brian Lehrer of NPR, considered the proposition: "Global Warming Is Not a Crisis". The audience, polled both before and after the debate, changed from opposing the proposition by 57% to 30% (13% undecided) to favoring it by 46% to 42% (12% undecided). The debate can be read or heard at http://www.npr.org/templates/story/story.php?storyId=9082151
Many of the most important considerations from both sides of the debate were presented both briefly and well by the participants. Brenda Ekwurzel (Union of Concerned Scientists), Gavin Schmidt, (climate scientist, NASA Goddard), and Prof. Richard C.J. Somerville (Scripps
Institute of Oceanography, University of California, San Diego) summarized the evidence for increasing concentrations of atmospheric carbon dioxide and for increasing mean global temperatures, including evidence that the past decade has been the warmest of the present interglacial epoch. They also tried to instill some confidence in the reliability of their computer models and their predictions of dangerously increasing temperatures. It is safe to say that credible projections of future global temperatures would be impossible without supercomputers.
Favoring the proposition were Dr. Richard S. Lindzen, (Prof. Atmospheric Sciences, MIT), Philip Stott (Emeritus Prof. Biogeography, U. London, UK), and Michael Crichton, (author and film maker). Lindzen made the point that the debate proposition was not a denial of global warming, but rather was concerned about potential human contributions and whether or not a crisis response was either necessary or desirable. Both he and Stott questioned the validity of the current computer programs for calculating future temperatures. Stott noted that many of the factors that can influence climate are poorly known and an important research effort into understanding connections between cloud formation, cosmic rays and solar magnetic activity has only begun. Crichton emphasized that significant reductions of future carbon dioxide
emissions could only be achieved by restraining industrialization in China, India and Africa.
The richer nations of Europe and America might be able to achieve significant reductions of
carbon dioxide gas emissions, and yet have little effect on concentrations of the gas in
the atmosphere. Thus the burden of reducing carbon dioxide levels might fall on the poorest
people of the world. In closing remarks, Crichton suggested that unless we can agree to ban private jets for the rich then we aren’t serious about the problem.
Pros and Cons in more detail:
The New York City debate was reasonably balanced, but it fell far short of being convincing for either side. The one consensus that was reached was that it would be very good to conserve energy and reduce greenhouse gas and other pollutant emissions. It is certainly true that by loading the atmosphere with carbon dioxide we are conducting an uncontrolled experiment on the earth. In my opinion it would be a very good thing if we minimized the rate at which we consume the finite resources of earth, but not at the expense of telling Africans and citizens of third world countries that they should not industrialize. So the questions before us are still (a) how serious is the problem and (b) what mitigation measures are appropriate? Here is how I view things.
If one takes the view that global warming is a serious problem, the claims are these:
1. There is clear evidence that the earth is warming at a rapid rate
2. The warming is a consequence of human activities
3. The consequences will be bad; and many may be catastrophic.
4. The scientific questions are settled. It is time for action.
Let’s examine these one by one.
(1) The most influential bit of evidence in favor of the first assertion is surely the “hockey stick” graph of Michael Mann. This graph shows global average temperature remaining virtually constant for a thousand years and then abruptly rising in the 20th century, culminating in the warmest temperatures ever in the last decade. The carbon dioxide concentration in the atmosphere shows a similar abrupt rise over the last century. At best the temperature graph is a monument to poor data analysis. It pretends that the medieval warm period, in which there were farms in Greenland, never occurred. Nor was there ever a “little ice age” in the 1700s when the Thames River froze over in the winters. The “hockey stick” graph has been discredited by a National Academy of Science report which states that the methodology used to produce it is unreliable beyond 400 years. If this period is replotted, the hockey stick is replaced with a much more gentle rise as temperatures have increased since the “little ice age” of the 1700s.
Taken at face value, the average of temperature measurements taken at different places on the earth surface shows increasing temperatures for about the past twenty five years. But the surface measurements have not been consistently taken. Increasingly, measurements are reported from urban areas with their well-known “heat island” effects and since the demise of the former Soviet Union, many stations from Siberia have been dropped from the averages. Although we are assured that efforts have been made to compensate for these biases, it is not clear that they have succeeded. The temperature increases shown by these averages are not in agreement with satellite measurements of temperatures in the troposphere. The latter show little warming until 2000 and then about half the amount measured on the surface since then.
Other proxies for temperature, such as the depth of the Greenland and Antarctic ice sheets yield inconclusive results. Ice seems to be thickening over the continental masses while breaking up around the margins. Smaller scale phenomena such as the disappearance of snow cover on Mt. Kilamanjaro are difficult to interpret. In that case, the drying of the air due to deforestation and agricultural activity is a more likely cause.
(2) If there is a “global warming signal” beginning to show in the temperature measurements, it is in its early stages, amounting to about 1 oF over the past 150 years, and its cause is not really known. But there is a physical basis for believing that human caused emissions of carbon dioxide would cause temperature increases. Most incoming solar energy enters the atmosphere as visible and near ultraviolet radiation. This is absorbed by clouds, oceans and soil and an approximately equal amount of energy is reradiated in the infrared region of the spectrum. If the infrared radiation is partially absorbed by water vapor, carbon dioxide or other gases in the atmosphere, not enough infrared escapes. The surface then warms until it can provide enough additional infrared radiation to maintain the balance between incoming and outgoing radiations. Trap more of the exiting infrared radiation and the surface temperatures will go up. Water vapor is by far the most important infrared absorber because there is so much more of it in the atmosphere than any of the other greenhouse gases. Nevertheless, carbon dioxide is an important absorber because it absorbs most strongly in the region of the strongest emissions of the exiting infrared. Former Vice Pres. Gore’s film showed a graph of carbon dioxide concentrations and temperatures in Greenland and Antarctic ice cores for a period of about 400,000 years, extending through several periodic ice ages (see 1999 Science, June 3) . It shows that rises in temperature and concentrations of carbon dioxide are strongly correlated. What he failed to mention is that temperatures at the end of the ice ages begin to rise, on average, about 600 years ahead of the corresponding strong rise of carbon dioxide concentration.
When all is said and done, the most widely accepted argument for global warming is provided by climate model simulations carried out on large computers. The rate at which carbon dioxide will accumulate in the atmosphere can be estimated from the present and extrapolated rates of fossil fuel consumption in the world. The climate models seem to have reached a consensus that the expected increase of carbon dioxide concentrations over the next century will cause the global mean temperature to rise by somewhere between 3oF and 20oF. In the past few years, the models have tended to converge toward the lower end of this range, but large uncertainties remain.
Much of the uncertainty in the model predictions is due to “feedback” processes. For example, rising temperatures will melt strongly reflective snow packs and expose darker soils and vegetation that then absorb more incoming solar radiation. This is a positive feedback that might be a cause of some of the warming of the last century as more land has been cultivated.. A negative feedback can occur if warmer oceans produce more water vapor in the air and more clouds form and block incoming radiation. However, low altitude clouds and high altitude clouds can have different effects. It is safe to say that the simulations of cloud cover are not yet adequate.
One of the first rules of simulations is that if there is a known history, then the model must be able to reproduce it. Key features of the situation can be built into the model and then the simulation run to see if the model reproduces results that were not given as input. A common model simulation is that used for oil reservoirs in order to maximize the recovery of oil. The reservoir size and the composition of its fluids are measured. The sequence of well placements and their measured initial pressures are provided as inputs to the simulation. If the model is correct, it will correctly reproduce the quantities of fluid produced and the subsequent reservoir pressures and then show how the distributions of oil, gas and brine change during the production process. A successful model may serve as a guide for further development wells or for gas reinjection or water flooding or other secondary recovery operations. But the key requirement necessary to obtain the investments for further efforts is that the model be able to faithfully reproduce the known reservoir history.
Climate models have not yet reached this standard. It is not yet possible to put in atmospheric conditions, including carbon dioxide concentrations from, say 1800 to 1900 and then add the carbon dioxide concentrations up to 2000 and correctly predict the climate for the past century. One of the reasons for this is that if the global mean temperatures are taken at face value, the earth warmed about 1oF from 1900-1940, cooled by about 0.2oF to 1979 and has warmed since then. The decades of cooling set off a great deal of media alarm about impending catastrophic global cooling, but it cannot be said that there was ever a corresponding consensus of climate scientists behind it. (This is probably due the fact that there were few climate scientists and those few lacked computers capable of dealing with the problem.) The present climate models have completely failed to reproduce this unsteady behavior of warming, cooling and resumption of warming. On the other hand, this complexity in the temperature variations is nicely matched in detail by solar magnetic field variations, but not by the carbon dioxide concentrations. Carbon dioxide concentrations have increased the most since 1940 but most of the century’s increase of temperature preceded them. The complex variation of temperatures is tightly correlated with solar magnetic activity, which increased from 1900 to 1940, decreased until the mid 70s and has strongly increased since 1980. Further, a strong correlation exists between sunspot (magnetic) activity and earth temperatures for the past several hundred years. The “little ice age” of the 1700s corresponded to an almost complete lack of sunspots.
Correlations in the absence of known physics are often controversial. Satellite measurements of solar output for the last twenty five years have shown very little variability of the solar power output over a complete solar magnetic cycle. Variability is roughly about one part per thousand of the solar output. So how could the sun have anything to do with recent warming? A connection currently being studied is that cloud cover is influenced by the ionization caused by the flux of cosmic rays entering the earth’s atmosphere. This earth can be shielded from this flux by the sun’s magnetic field, which has dramatically increased in strength over the last century and markedly within the last twenty years. Recent work has shown that cloud cover over the Pacific is strongly correlated with cosmic ray flux. In my opinion, the computer simulations are not yet adequate and may lack important inputs. I find it hard to believe that they can provide accurate projections for the next hundred years.
(3) Global mean temperature is projected by the computer models to rise by about an additional 1 oF by mid-century. If the models would be correct and we have done nothing to reduce carbon dioxide emissions, the stage will be set for inescapable subsequent temperature increases and some of the consequences will undoubtedly be bad. The most extreme predictions of melting of polar caps and catastrophic rises of sea level most certainly will not occur if only because the time scale for these responses is much longer than one century. The alarmist prediction of increasing extreme weather events is also likely to be wrong. Polar regions are expected to warm more than equatorial and mid-latitude zones. Since pole-equator temperature difference is the primary driver of the weather system, one should expect less variability rather than more. Persons claiming that the hurricanes of 2005 are already examples of what to expect show an appalling lack of knowledge of normal weather variability. There is a consensus among scientists who study weather patterns that there is neither evidence for recent abnormal variability nor reason for expecting any. On the other hand, more temperate climates in Canada and Siberia might provide more arable lands with which to feed the hungry people of the world. Whatever the cause of global warming, there will be winners and losers and life will go on as it has during various millennia known to have both warmer and cooler climates.
(4) The debate over global warming is taking on an uncivil tone. The motives of climate scientists on both sides of the debate have been questioned. It is claimed that some climate scientists have become alarmists in order to attract additional funds for studies. On the other hand nearly every climate scientist who questions the need for urgent effort to mitigate global warming is accused of having sold out to oil company or other major industry interests. Lately they have been called “global warming deniers” in analogy to the deniers of the WWII holocaust. This is unfortunate, but for the record, the debate over global warming is not over. There are large numbers of well credentialed and respectable scientists who remain skeptical about the reliability of climate models and question the need for urgent action. During the past 2 years, more than 17,100 basic and applied American scientists, two-thirds with advanced degrees, have signed the Global Warming Petition (see http://www.oism.org/pproject/s33p357.htm). Signers of the petition so far include 2,660 physicists, geophysicists, climatologists, meteorologists, oceanographers, and environmental scientists who are especially well qualified to evaluate the effects of carbon dioxide on the Earth's atmosphere and climate. Signers of the petition also include 5,017 scientists whose fields of specialization in chemistry, biochemistry, biology, and other life sciences make them especially well qualified to evaluate the effects of carbon dioxide upon the Earth's plant and animal life. These comments are intended only to counter the idea that the debate is over. In truth it has hardly begun. If we want the truth, government funds for climate studies should be provided to researchers on both sides of the question. As in several other areas of science, the peer review system for distributing funds for studies is under the control of a dominating orthodox view and it needs to be fixed.
In the current caustic debate climate, we should keep in mind that the nations of the world reached agreement to limit production of light flouro-chlorocarbons in order to protect the ozone layer of our atmosphere. In that case, the science was clear on cause and effect and a genuine consensus was reached. The appropriate and necessary actions and costs were known and we got the job done. When the science is clear and effective, and viable energy alternatives become available we will likely respond to the problem of carbon dioxide emissions as well. A “carrot and stick” approach to the problem by governments, such as was used to raise the fuel efficiency of motor vehicles would seem to the best approach. But it will not be as easy as banning freons. Often the difference between a good idea and a bad one is a quantitative matter and that is the case with combating carbon dioxide emissions. World oil consumption amounts to roughly 70 million barrels per day. For the sake of argument suppose that the weight of each barrel is converted to carbon that subsequently combines with oxygen as carbon dioxide in the atmosphere. This would add about 2 parts per million (ppm) of carbon dioxide to the atmosphere annually. Burning of coal produces a similar increment of carbon dioxide. But measured concentrations of atmospheric carbon dioxide have been increasing at only about 1 ppm/yr for the past twenty five years. Clearly a large amount of the carbon dioxide must be sequestered in plant growth and in the oceans. This is especially evident in the reforestation of North America as people have migrated from farms to the cities during the past century. Considering the amount of carbon sequestered, the increase of atmospheric carbon dioxide concentration since the beginning of the industrial revolution is about what would be expected from the total amount of carbon dioxide produced by human use of fossil fuels. The seasonal variations in carbon dioxide concentration are about 6 to 8 ppm in the northern hemisphere and clearly show the effect of plant growth cycles. It is also clear that completely stopping further increases of carbon dioxide would require either a complete ban on burning fossil fuels or capture of the carbon dioxide that they produce.
As a practical matter, unless we can replace at least half of the energy we obtain from fossil fuels with fuels that produce no carbon dioxide, we won’t be able to do much about the production of carbon dioxide. The political reality is that the third world nations need to develop in order to improve living standards for humans. The fuel that they have in abundance is coal. The only way to mitigate the problem of increasing production of carbon dioxide is to capture most of it where it is produced in electrical power generating plants. Otherwise there is no realistic chance that anthropogenic carbon dioxide emissions will be reduced at all within the next thirty years. Stopping every vehicle and power generation plant in the west would only maintain the status quo as China, India and Africa develop and begin to relieve the grinding poverty and disease that afflicts half of all humans.