The Question of Global Warming

The current debate on global warming provides an interesting subject for use of the “probabilistic rationalism” model.  Although not usually framed in this manner, the debate actually consists of a sequence of questions rather than the all-inclusive single question of whether or not human activity contributes significantly to a current trend of rising global temperatures.  In examining how this debate might be approached using “probabilistic rationalism” we need to specify the sequence of component questions and arrive at probability estimates for each in turn throughout the sequence.

In conducting this exercise, the following sequence of questions will be examined.

1. Is there a current definite trend of global warming?
2. If so, is the warming trend progressing at an unusually rapid pace?
3. If so, is the warming a result of accumulating greenhouse gases?
4. If so, is carbon dioxide the primary greenhouse gas responsible?
5. If so, is human activity particularly responsible for an accelerated accumulation of carbon dioxide in the atmosphere?
6. If so,are there likely to be devastating consequences of global warming caused by this human activity, and finally
7. are there practical policies and/or actions that could be implemented that would prevent or significantly limit these adverse consequences?

While this sequence is not necessarily exhaustive, it is sufficient to allow for a meaningful analysis and to provide the basis for reaching an informed conclusion with an associated probability of being correct.

Before considering the sequence of questions, we should understand several basic points.  Very few scientific issues, if any, have been resolved to the point of being an absolute fact with no degree of uncertainty.  Even our most fundamental laws of physics break down under certain extreme cosmologic conditions.  Scientists recognize that virtually all constructs, whether theory or law, have some associated degree of uncertainty.  In this sense, the above questions all involve a degree of uncertainty that can range from very little to quite large.  Insufficient or conflicting data, conflicting interpretations of data, as well as unknown or unknowable information are common causes of uncertainty. When we consider each question in the sequence and suggest an answer with an associated probability of being correct, that result is a personal impression and is based on limited exposure to and knowledge of the actual scientific data involved.  Thus, conclusions reached in this way are only valid for the individual or group conducting the analysis.  They are not absolutes.  However, they are results obtained via a rational process.

Please note that the quantitative data statements providing the basis for the following analysis have been abstracted from a variety of internet and other sources (complete bibliography available upon request).  These data have been referenced by the author to illustrate how a non-expert in the physical sciences can reach a rational conclusion that there is a relatively low probability that human activity is playing a significant role in causing global warming.

Question #1 - Is there a current definite trend in global warming?

Many, but not all, scientists feel that there is a current, definite, trend in global warming.  Why are there also a number who do not agree?  Isn’t this simply a matter of factual data, i.e., just observing the historic record of increasing global surface temperatures?  In order to understand the position of those who question the reality of a warming trend,  perhaps we should revisit the concept of “scale” and also look more closely at the nature of the data.  With regard to scale, in this case, we are interested in the scale of time.  The earth is believed to be approximately 3.8 billion years old and geologic records strongly suggest that there have been repeated, but irregular, cyclic changes in global temperatures.  These are relatively slow cycles that occur over the course of decades, centuries or even millennia and have led to alternating periods of warming and cooling with associated tropical and ice ages of global proportions.  Humans have been on the earth for only about 100,000 years.  Temperature measuring devices were first invented in the early 16th century and it is likely that systematic measurements of earth surface temperatures have only been made in the past 200 years. In order to appreciate the relatively brief time that man has been capable of recording global temperatures, it is insightful to put the age of the earth on a scale such that its 3.8 billion years is represented by 1 year or 365 days.  On this scale, humans have been around for only the past 13.8 minutes and have possessed temperature measuring devices for only the past 1.7 seconds.  In other words, our ability to make any kind of reliable estimates regarding global climate trends based strictly on direct human observation is extremely limited relative to the age of the earth and the length of the historic temperature cycles.  Thus, much reliance must be placed on interpretation of historic surrogate geo-chemical or biologic clues.

With regard to determining a global temperature for any given point in time, it should be appreciated that any overall surface temperature recorded is actually a mean of a number of individual readings taken from a finite number of global locations.  When one considers the broad range of temperatures found on the earth at any given point in time and the infinite possibility of measurement sites, the temperature history record represents a semi-quantitative construct rather than an absolute.  In fact Danish physicist Bjarne Anderson points out that the notion of a specific global temperature for any given point in time is meaningless and that such a concept is only valid for homogeneous systems.  However, as long as the measurement sites remain constant, the record should provide a reasonable idea of trends.  One potential problem with an assumption of constant sites is that 75% of the earth is covered by water and keeping sites constant over that portion of the earth may be problematic. Nevertheless, the following is a summarized history of the earth’s climate constructed from the surrogate clues and provides an idea of just how variable estimated global temperatures have been over the long haul and just how irregular the fluctuations have been.

Earth's Climatic History

Various techniques, primarily dependent on surrogate evidence, have been used by climatologists to reconstruct an historical record of the Earth's past climate. A concise summary of this history has recently been presented by Dr. Michael Pidwirny (http://www.physicalgeography.net/fundamentals/7xhtml).  He points out that global temperatures were probably 8 to 15° Celsius warmer than today during most of Earth's past history and that during the last billion years, warmer conditions were broken by glacial periods starting at 925, 800, 680, 450, 330, and 2 million years before present.

The following is a brief summary of the Earth’s climate history, beginning with the most recent glacial period, as outlined by Dr. Pidwirny:

The Pleistocene or Ice Age - From 2,000,000 - 14,000 B.P. (before present) - characterized by large glacial ice sheets covering much of North America, Europe, and Asia for extended periods of time. Glacial periods were periodically interrupted by warmer interglacial periods but during the coldest periods, average global temperatures were probably 4 - 5° Celsius colder than they are today.

The Holocene epoch - (12,000 BC - present) is a general period of warming as the earth emerges from the last ice age and is characterized by alternating periods of warming and cooling including today’s most recent period of warming and glacial retreat.

The Younger-Dryas - (about 10,000 - 8500 BC) - a temporary interruption in the Holocene epoch characterized by a sudden cooling.  It’s thought that that this cooling may have been caused by the release of fresh water trapped behind ice with the subsequenty shifting of ocean currents and heat exchange with the atmosphere.

Resumption of warming by 8500 BC with the Climatic Optimum reached by 5000 - 3000 BC during which time the maximum temperatures during the Holocene were reached and were 1 to 2° Celsius warmer than they are today. During the climatic optimum many of the Earth's great ancient civilizations began and flourished. In Africa, the Nile River had three times its present volume, indicating a much larger tropical region.

Additional alternating periods of cooling and warming occurred as follows:

Cooling trend (3000 to 2000 BC) - large drops in sea-level and the emergence of many islands (e.g. Bahamas) and coastal areas that are still above sea-level today.

Warming trend (2000 to 1500 BC)

Cooling trend (1500 - 750 BC) - renewed ice growth in continental glaciers and alpine glaciers, and a sea-level drop of between 2 to 3 meters below present day levels.

Warming trend (750 BC - 150 BC)

Cooling trend (150BC - 900 AD) - Marked by freezing of the Nile River (829 AD) and the Black Sea (800-801 AD).

Warming trend (900 - 1200 AD) - The Little Climatic Optimum representing the warmest climate since the Climatic Optimum (Vikings established settlements on Greenland and Iceland and snow line in the Rocky Mountains about 370 meters above current levels)

Cooling trend (1200 - 1850AD) - Great drought in the American southwest (1276 - 1299AD) with floods, great droughts and extreme seasonal climate fluctuations up to the 1400s. During the “Little Ice Age” (1550 - 1850 AD) global temperatures were at their coldest since the beginning of the Holocene (the average annual temperature of the Northern Hemisphere was about 1.0 degree Celsius lower than today).

Warming trend (1850 AD to present)

While the above history is generally accepted, there remains considerably uncertainty regarding this model.  As described previously, the period of direct temperature measurements by modern man is remarkably brief relative to the age of the earth.  The significance of trends suggested by the limited, surrogate, data involves considerable speculation and, in fact, certain scientists cite data (e.g. atmospheric temperature measurements and growing sea ice around antarctica during the last 20 years) that suggests global cooling may actually be the more likely current long-term trend.

In taking into account my understanding of the available information and making a personal appraisal of the overall picture painted by science, my position is that there is a 90% probability that we are in a period of global warming.

Question # 2 - If we are in a period of global warming, is the warming trend progressing at an usually rapid pace.

An affirmative answer to this question is the first key assumption made by advocates of human-induced global warming and is critical to their argument.  The basis for this, so called, “hockey stick” shape to the graphical presentation of global temperature history is an image produced by Mann, Bradley and Hughes in a 1998 publication.  In that analysis, the blade of the hockey stick represents a sharp upturn in global temperatures between 1900 and 2000.  It is this apparent upturn which correlates with the age of industrialization that has fed the current movement in blaming recent global warming on human activity.  Furthermore, this analysis forms the foundation of the IPCC position on global warming.

Without going into detail, the results reported by Mann, Bradley and Hughes have been seriously questioned by some members of the scientific community.  The report has been criticized for relying on a “selective and inappropriate” presentation of results where key pieces of data were omitted.  The debate regarding the quality of the Mann, Bradley and Hughes science and the validity of the “hockey stick” pattern is far from being resolved.  A report by Richard Muller exemplifies the kind of criticism currently faced by Mann, Bradley and Hughes (http://www.technologyreview.com/Energy/13830/).  The following  summarizes points made by Muller:

A fundamental mathematical flaw in the computer program used to produce the “hockey stick” was uncovered by Canadian scientists Stephen McIntyre and Ross McKitrick. A standard method used by Mann, principal component analysis, or PCA, was found to be flawed in that the program did not do conventional PCA and handled data normalization in a way described as mistaken.

Consequently, the improper normalization procedure tended to emphasize data that had  the hockey stick shape and suppressed data that did not.  The significance of this flaw was reportedly demonstrated when random data, generated using Monte Carlo analysis and fed into the Mann procedure, yielded the hockey stick shape. 

It is also interesting to note that since 1998 global temperatures have been relatively constant.

My own assessment is that there are serious questions regarding the “hockey stick” pattern in global warming that have not been satisfactorily addressed.  A 60% probability of this “hockey stick” pattern may be overly generous.

Question  #3 - If there is an unusually rapid pace of global warming, is it a result of accumulating greenhouse gases?

The greenhouse gas cause of global warming is another key concept in the assertion of a significant human role in global warming.  The argument is based on recent increases in atmospheric CO2 levels and correlations of greenhouse gases with temperature obtained from ice cores.  Minute air bubbles in the ice reveal levels of various atmospheric component gases at particular points of time in the past.  While scientists generally agree that such a correlation between these gas levels and temperature appears to exist, there is disagreement about which came first.  Some analysis indicates that temperature raises were followed by elevations in atmospheric CO2 rather than the other way around.  If so, rising temperatures could not have been caused by elevated levels of greenhouse gases but rather, elevations in these levels have more likely been caused by rising temperatures.  Furthermore, if recent elevations in surface temperature were caused by an enhanced greenhouse effect, there should have been a similar rise in temperature of the lower atmosphere.  Recent reports indicate that only a smaller, non-parallel rise in temperature has been observed in the lower atmosphere.  On the other hand, a number of scientists have looked at the relationship between solar activity and global temperature and report a much more positive correlation than is seen between greenhouse gases and global temperature.  In this regard, it’s also interesting to note that temperatures on Mars have reportedly increased in recent years. 

My assessment of the probability that global warming is primarily caused by increasing concentrations of greenhouse gases in earth’s atmosphere is no greater than 50%.

Question #4 - If greenhouse gases are responsible for global warming, is CO2 the primary greenhouse gas responsible?

95% of the greenhouse gas in the atmosphere is water vapor.  The remaining 5% is largely CO2 with methane and several other gases making small contributions. 

Given the relatively small proportion of greenhouse gas that is CO2, it’s difficult to understand how CO2 can play such a major role.  Additionally, climate history data provide  examples where past atmospheric CO2 levels and temperature moved in opposite directions.  My assessment, given the current status of conflicting data, is, as with the previous question, a 50% probability of an affirmative outcome.

Question #5 - If increased level of CO2 in the atmosphere is the principal cause of current global warming, is human activity primarily responsible.

CO2 arising from human activity is small compared to natural sources of CO2 including volcanic activity and the world’s oceans.   By far, the greatest source of CO2 is the earth’s oceans.  Human activity only accounts for a small fraction of the total CO2 in the atmosphere.  When all sources of CO2 are taken into account, the maximum contribution of human CO2 sources to greenhouse warming has been estimated to be as low as   1%.  Furthermore, most of the recent global warming trend took place in the first half of the 20th century when human production of CO2 was relatively low.  As previously pointed out, No significant warming has occurred during the past 9 years.  Certainly human activity has had no role to play in recent temperature elevations on Mars nor in the broad fluctuations in earth’s temperature during the 99.997% of earth’s history prior to the evolution of the human species.

My own impression is that the probability of human activity being primarily responsible for elevated atmospheric levels of CO2 is very low, but for argument’s sake we’ll assume another 50%.

Overall Probability of Questions 1 - 5 being positive is calculated as a conditional probability sequence:  P1 * P2 * P3 * P4 * P5    (.90 * .60 * .50 * .50 * .50)  = 0.0675  or about 7%.  Because of the low probability at this stage, the added analysis of questions #6 and #7 is would seem to be unnecessary.  However, it should be pointed out that serious doubts exist regarding  an affirmative outcome for each of those questions and this would likely further reduce the overall final probability of the seven question sequence to something in the range of < 5%.  It should be emphasized that even if we elevated the probabilities of questions 2 - 7 to 80%, the final conditional probability would only be about 37% for the 5 question sequence and 24% for the seven question sequence.  The significance of this result is due to this being a situation where the issue is complex, consisting of multiple questions, each possessing a substantial degree of uncertainty.

In summary, using the probabilistic rationalism method, this analysis suggests to me that there is a low probability (7%) that human activity plays a significant role in global climate change, especially global warming. Additionally, the conclusion reached using this systematic approach is consistent with the intuitive sense that one gets by carefully considering the scale factors involved.  Do we truly believe that human activity can modify the climate on a global level.  While human activity can certainly modify conditions locally, e.g. smog and air pollution over certain cities, pollution of lakes and rivers, etc., changing overall global climate is many orders of magnitude greater in scale.  Humans have shown no ability to change climate or even to modify relatively weak weather systems.  We can’t prevent tornados, redirect the paths of hurricanes or change the path of a rain or snow event.  The most we have ever been able to do is to seed clouds to tease out a light rain.  The entire mass and might of humanity is many orders of magnitude weaker than that of the sun.  In my own opinion, it’s far more likely that global climate changes are caused by powerful natural factors such as solar activity, variations in earth’s orbit, variations in cloud formation and precipitation as well as occasional more violent events such as super volcanic eruptions and asteroid impacts.

In conclusion, I feel that there is a better rationale for encouraging solutions to the problems associated with continued heavy dependence on fossil fuels.  Not only are fossil fuel sources limited, they are unevenly distributed throughout the world.  This almost ensures escalating conflict as nations vie for this shrinking vital resource.   All reasonable efforts should be taken to avoid pollution of both air and water as new energy sources are developed and implemented. In short, there are good, valid, reasons to pursue new energy sources, energy conservation and to limit pollution of air and water as much as possible. Low probability stories such as that invoking human-induced global warming are unnecessary and likely to be counterproductive in gaining wide-spread public support for reasonable approaches.  While leadership, encouragement, and positive incentives provided by government may well be beneficial, there should be no need to turn back progress with invasive government programs or punitive penalties and taxes.  Such a course serves only those with an agenda that is clearly not in the best interests of strong and prosperous United States unburdened by excessive government control.