Skip to comments.Is global warming caused by human activity?
Posted on 01/08/2009 11:57:18 AM PST by pjd
I wrote this about six months ago, but never posted it. The version I've posted here doesn't have images.
A link to an html version with images is here and a PDF version of the article is here
A great number of facts and declarations are often presented with regard to global warming and Mankind's role in it. Most of these assertions are derived from the following clear and simple line of reasoning:
|Fact:||CO2 is a greenhouse gas whose presence in the atmosphere can cause Earth's temperature increase.|
|Fact:||Since the beginning of the industrial age,|
Based only on these facts, it is reasonable to conclude that post-industrial age human activity is the cause of recently observed global warming. It is also reasonable to speculate that continued production of CO2, at current or higher rates, will continue to drive the temperature still higher, perhaps to catastrophic results.
However, a conclusion based only on these facts is, in fact, a good example of how a little knowledge can be a dangerous thing. To understand this, let's take a moment to consider how Science works and what is required of it to make a valid scientific conclusion.
How Science works
Initially, a scientist starts out with a hypothesis which is often formed on the basis of observations. However, the hypothesis may come from virtually anywhere - a dream, a guess,...it doesn't matter. The point is, once a hypothesis is formed, the first task is to try to disprove it (falsify it.) If the scientist is unable to falsify the hypothesis, a next step is to publish it so that other scientists can attempt the falsification process. If their attempts at falsification also fail, then the hypothesis earns a measure of credibility.
Furthermore, if the hypothesis represents a new or alternate explanation for a phenomenon which already has an established theory or explanation, there is an additional hurdle that the new hypothesis must clear. The new hypothesis must show that the established theory is insufficient to explain some observable phenomena which the new hypothesis can explain and the new hypothesis must also be able to explain or be consistent with the all of the other phenomena which the earlier theory could successfully address. Essentially, the bar is higher for new explanations.
One thing a scientist does not do is try to prove that a hypothesis is correct. That would be the nature of pseudo-science and represents a logical error known as improper induction. This is because it is easy to obtain evidence in favor of virtually any hypothesis, but all it takes is one contradicting example to invalidate the conclusion. This concept of falsification is a central theme of Karl Popper's Theory of Demarcation and was also eloquently phrased by Albert Einstein when he said,
The global warming hypothesis
Science also recognizes certain phenomena to be true, even if we don't fully understand the processes responsible for the observed phenomena. For example, you may know that magnets attract or repel each other without understanding the physics of magnetism. You may know that the Earth has a moon without knowing where it came from.
Similarly, we know that the Earth has undergone many global temperature fluctuations long before humans existed. Even though we don't know or understand the details responsible for those changes, we know they were the result of natural processes and not caused by Man. Hence, we know that the ability for natural processes to cause global temperature changes is beyond refute.
Therefore, in order to justify the new proposition: That recent global warming is not the result of natural processes but is instead the result of human activity, it must be shown that
Each of these points must be true in order to conclude that human activity is the cause of recent global warming.
Let's consider these three points, one-by-one...
Global warming is taking place
true or false?
The answer to this question depends on the period of time we consider. For example, over the last 2000 years1,2 the temperature trend has been generally downward (cooling.) Over the last 700 years the trend has been constant and during the 19th and 20th Centuries, the trend has been upward. The current warming trend began about 1800. At that time, the Earth had just come out of a relatively cold period we call the Little Ice Age. According to the U.S. National Oceanographic and Atmospheric Administration (NOAA), National Climatic Data Center3, the temperature trend for the 20th Century (1895 to present) was 0.1 degrees F per decade. This trend, however, was not a straight-line, steady trend. In fact, most of the 20th Century warming occurred between 1910 and 1940$4. That was followed by a cooling trend from 1940 to 1975 (which resulted in world-wide fear of an impending Ice Age.) That cooling was then followed by another warming trend through 1998. However, during the last decade, 1998 to 2008 there has been a net cooling of 1.1 degrees F (0.6C)5. The recent cooling has brought temperatures back to their 1980 levels, which is where we were shortly after the 1940 - 1975 cooling and approximately to the level at the beginning of the 20th Century.
So, is global warming taking place? Over the last ten years, there has been global cooling. The last hundred years has seen warming. The last 2000 years has been cooling, The last 10,000 years has been cooling. The last 200,000 years has been warming. It's a matter of choosing a time-scale. A 30-year trend was long-enough to prompt fears of a coming Ice Age (which turned out to be short-lived.) Then, after only a ten-year warming trend, new concerns about catastrophic warming began (and that warming only continued for another ten years, to 1998). Now we are ten years into a new cooling trend. Clearly, a few tens of years are not enough to establish a long-term trend. It is probably fair to say that the last 200 year warming trend is a recovery from the Little Ice Age and that the warming was a real trend. But we cannot say if more warming is in store or if the present cooling trend will continue. So it is impossible to say, at this time, if there is global warming or not. Therefore, Point 1 stands as neither true nor false. (Remember, Point 1 must be true in order to conclude that human activity is the cause of global warming.)
Natural causes cannot account for the present warming
true or false?
For the purpose of this discussion, we will define `natural causes' as any causes which are not the result of human activity. In the context of global warming, human causes are any phenomena which result from large amounts of CO2 produced by human activity. This limits the influence of human activity on global warming to within the last hundred years when quantities of human-produced CO2 became significant.
By looking at climate variations which occurred longer ago than a hundred years, we can gain insight about natural variations and natural causes. Then we can determine if the current climate behavior is within the domain of natural variation.
On very long time scales6, as shown in Fig. 2, we see that there have been at least four warm and cold periods of major proportions. The warm periods are characterized by temperatures about 10 degreesC warmer than we see today. The warm periods are typically about 100 million years in length. Between the warm periods are the major ice ages, which typically last a few million years. The ice ages feature temperatures which are similar to what we see today. In fact, most geologists believe that we are still in the the midst of the most recent ice age.
The major ice age cycles are believed to be related to changing land mass positions (Continental Drift) which affect the ocean currents and distribution of heat. From the figure, note that there is essentially no correlation between atmospheric CO2 levels and the major Ice Age cycles.
On a somewhat shorter time scale, like millions or hundreds of thousands of years, we can consider the glacial and interglacial periods which have occurred within the present Ice Age. These periods correlate well with the Milankovitch Cycles which are related to variations in Earth's orbit, rotation and tilt. Although the correlation of the Milankovitch Cycles with climate variation is very good, the variations in solar flux due to the orbital variations are not, by themselves, sufficient to to account for the observed glacial/interglacial temperature variations. However, this has been explained through a positive feedback mechanism: Longer snow seasons resulting from Milankovitch cooling bring about increased reflectivity which add to the cooling and further increases the reflectivity, etc., and is sufficient to lead to the observed results.
On somewhat shorter time scales (tens of thousands of years) we finally see some correlation between temperature and CO2. But in all cases, we see that changes in CO2 follow changes in temperature by about 800 years. Because changes in temperature occur before changes in CO2 levels, changes in CO2 levels cannot possibly be the cause of the observed changes in temperature.
However, it is simple to understand why temperature controls CO2 and why there is a several hundred year delay. It is explained by the fact that the solubility of CO2 in water is inversely proportional to temperature (see Fig.3). When the oceans warm, they release CO2. When the oceans cool, they absorb CO2. You can demonstrate this principle yourself by pouring a room-temperature glass of soda and leaving it sit at room-temperature, and also pouring a cold glass of soda and letting it sit in the refrigerator. The warmer glass will lose its `fizz' within minutes while the colder glass retains much more. The `fizz' is CO2 dissolved in the water. Furthermore, since the oceans have a very large heat capacity compared to the atmosphere, it takes hundreds of years for the ocean temperatures to respond to changes in atmospheric temperatures.
On still shorter timescales, we can consider solar variability. There are several different solar cycles, typically on the order of tens of years. Like the Milankovitch cycles, there is a very good correlation with temperature and solar activity. Since the correlation is good and since it is not possible for the Earth's temperature to affect solar activity, it must be true that solar activity affects Earth's temperature. An aspect of this theory which is not completely understood is that variations in solar luminosity are not, by themselves, sufficient to account for observed changes in temperature. Therefore, a feedback mechanism must also be involved. One such mechanism has been proposed which is based on the observation that increased solar activity is also accompanied by increased solar wind which shields the Earth from cosmic rays. Cosmic rays, meanwhile, have been shown to play a role in cloud formation. So when the sun is more active, the solar wind deflects more cosmic rays. This leads to a decrease in low-altitude cloud formation, permitting more sunshine to strike the Earth. This feedback appears to be sufficient to account for the remaining temperature variation.
The data in Fig. 4 show that solar irradiance correlates well with Arctic temperature while hydrocarbon use does not. Although this positive correlation between temperature and solar irradiance does not necessarily prove that solar irradiance is the cause and temperature is the effect, there is no known physical mechanism by which temperatures in the Arctic are able to affect the output of the sun. Therefore we must conclude that either the variations in solar activity are driving the observed temperature trends in the Arctic or that there has been a 120 year coincidence between every fluctuation of Arctic temperature and solar irradiance.
So far, we've shown what we already knew from the beginning, that natural processes can cause global warming. However, we still have to answer the question as to whether natural causes can explain the currently observed warming trend.
If the current temperature trend can be shown to be outside the limits of what we know to be natural variability, then a strong case can be made for an un-natural or man-made cause. So let's look at the recent trends compared to the past natural behavior.
Within the context of historical temperature patterns, as shown in Fig. 5, there does not appear to be anything whatsoever unusual or beyond the limits of natural variability in the current temperature patterns. Therefore we must conclude that natural phenomena are capable of explaining the presently observed warming. So Point 2 is false. (Point 2 must be true in order to conclude that human activity is the cause of global warming.)
Human activity can account for the present warming
true or false?
As we've noted earlier, there has been an approximately 0.1 degree F per decade rise in temperature over the last hundred years. Could this be the result of human activity?
To address this question, let us first appeal to some basic rules of logic so that we may quickly and easily disqualify some obviously invalid lines of reasoning.
Evidence of warming is often presented as evidence of human-caused warming, The logical construction of this argument is as follows:
If human activity causes global warming, then the Earth will warm.
The Earth is warming.
Therefore, human activity causes global warming.
This argument is invalid because the conclusion is drawn from a common logical error known as the converse error. As a clarifying example of a converse error, consider the argument:
If Joe drops the glass, the glass will break.
The glass is broken.
Therefore Joe dropped the glass.
The conclusion that Joe dropped the glass is invalid because the glass might have been dropped by anyone else, or it could have been broken by some entirely different means. By the same logic, evidence of warming is simply evidence of warming. No conclusion about the role of human activity can be drawn from it.
Another invalid argument is the claim that, ``If there is a consensus of scientists that global warming is human-caused, then human-caused global warming must be true.'' This argument is invalid for at least two reasons: First of all, the premise is not true. There is not a consensus of scientists as proved by a recent petition of 32,000 scientists who object to the premise. However, even if there were a consensus, it is still a logically invalid conclusion by reason of improper induction. Consider, for example, the consensus of scientists long ago who believed the Sun and stars revolve around the Earth. Clearly, consensus doe not make it true.
Computer climate models do not provide evidence of human-caused global warming. There are many reasons to discount the predictions of the computer climate models. Most importantly, is the fact that the computer models are not real and they have not been validated against real observations. The validations have consisted of comparing one computer model to another. Meanwhile, there are significant uncertainties at all levels of the models. These uncertainties include the primary energy source (the Sun,) physical processes (such as cloud formation and their role in climate, the values of many physical parameters, and the boundary conditions. In addition, limitations of computer resources prevent the use of small enough grid-size to resolve many important features. The system is extremely non-linear and sensitive to all of the above mentioned uncertainties and limitations. Any one uncertainty is sufficient to produce unreliable results.
The fundamental mechanism through which human activity is believed to affect global temperature is based on the greenhouse gas effect of atmospheric CO2. This effect is combined with the additional premise that human activity produces quantities of atmospheric CO2 that are, presumably, large enough to affect global temperature (through the mechanism of greenhouse gas warming.) This is a valid line of reasoning, and should be examined.
Greenhouse gas theory is often explained with an overly simplified (and incorrect) model. The typical overly simplified model is represented in Fig. 6, from the British National Space Center. This model depicts the cooling of the Earth by thermal radiation from the surface. One of the reasons this model is incorrect is because the surface of Earth is not cooled primarily by thermal radiation.
|Fig. 6 Overly simplified model of greenhouse gas phenomenon.||Fig. 7 More realistic greenhouse model. Lighter shading represents reduced opacity due to diminishing water vapor density.|
A more accurate (but still simplified) greenhouse gas model is depicted in Fig.7. In this model, the effect of water vapor, the main greenhouse gas, is strongest near the Earth's surface in the tropics. The effect decreases sharply with both altitude and latitude. The dark bands indicate the largest effects while the lighter bands indicate diminishing effects as latitude and altitude increase.
In the tropical latitudes near the surface, there is sufficient greenhouse opacity that the surface cannot effectively cool by thermal radiation emission. As a result, heat is conducted away from the surface by fluid motions (shown by solid lines in Figure 7.) These motions carry the heat up in altitude and in latitude (toward the poles) to levels where it is possible for thermal radiation emitted from these levels to escape to space, shown by the wavy line.
This is how the standard greenhouse gas model works. Indeed, all climate models predict that, if greenhouse gases are driving global warming, there will be a unique `fingerprint' of the effect in the form of a warming trend in the tropical troposphere which increases with altitude. Furthermore, since climate changes due to solar variability or other known natural factors will not show this characteristic pattern, this is a good test of the greenhouse hypothesis.
Putting in some numbers, Lee et al. (2007) investigated four different General Circulation Models to examine how temperature, according to the models, should change with CO2. Accordingly, and for all four models, the warming trend at high altitude in the tropics should be two to three times larger than the trend at the surface.
We have good observational measurement of the temperature in this region of the troposphere. The records show that, at least since the 1960s, the temperature trend in the troposphere is about three-quarters of the surface trend. It is not 2 to 3 times larger, as predicted by the greenhouse models. From this, we must conclude that either the greenhouse model is fundamentally wrong, the surface temperature measurements are in error, the troposphere temperature measurements are in error or greenhouse warming is much smaller than expected. If the physics is good and the measurements are good, we must conclude that the warming is not driven by the greenhouse effect, and therefore not related to human activity.
If the greenhouse theory is true, global temperatures should rise in response to increases in atmospheric CO2. However, looking back at Fig. 4, we see that carbon use was increasing exponentially during the period 1940 to 1970, yet the Arctic temperature was declining during that same period. Also, as described in Sec. 2, for the past several hundred thousand years, changes in atmospheric CO2 levels followed changes in temperature by a period of several hundred years. This behavior is not consistent with CO2 causing changes in temperature.
Furthermore, if CO2 were the primary driver of temperature, then temperature would increase with increasing CO2. But we also know that increasing temperatures would release even more CO2 from the oceans. That, in turn, would drive the temperatures higher still. By the nature of this logic, temperatures would never come down. This situation is contrary to the historical record which features many cycles in which temperatures and CO2 levels have risen, and then then fallen.
In this section, we have shown that 1.) The expected physical evidence for greenhouse gas warming is not present; 2.) The expected cause and effect relationship between temperature and CO2 is not present; 3.) The greenhouse model is inconsistent with established historical cyclical patterns. Based on any of these three observations, we must conclude that the statement ``Human activity can account for the present warming,'' is not true.
Recall our conditions that, in order to justify the new proposition that recent global warming is not the result of natural causes but is, instead, the result of human activity, the following conditions must be true:
What we've shown in the previous sections is that Condition 1 is not true. Condition 2 is not true and Condition 3 is not true. Since all three of these conditions must be true in order to justify the theory of human-cause global warming, we must conclude that there is no logical basis on which to believe that theory.
One can also look at this situation from a more practical point of view.
On the one hand, we have the natural explanation.
There is good correlation between temperature and Earth's orbital variations.
There is good correlation between temperature and solar variations.
There is historical evidence of natural climate cycles.
There is historical evidence that changes in temperature cause changes in atmospheric CO2.
There is scientific basis for each of these observations.
On the other hand, we have the anthropogenic greenhouse gas explanation.
The physical evidence for greenhouse gas warming is absent.
The correlation between CO2 and temperature is absent.
The historical evidence is not consistent with CO2 acting as a driver of temperature.
Temperature trends during the most recent decade have displayed the exact opposite behavior than predicted by the greenhouse theory.
In light of these observations, by what logic can we justify choosing a new theory which has no supporting physical evidence, no positive correlation with observations, inconsistency with historical evidence and currently predicts the opposite of what we now observe?
Furthermore, by what logic do we choose such a theory over an established theory that has physical evidence and positive correlation with observations, is consistent with the historical record and currently predicts what we now observe? (We are currently witnessing a decrease in solar activity and a corresponding decrease in global temperature, as expected.)
“Is global warming caused by human activity?”
According to the left global warming is caused by mankind......but when presented with evidence that the global temperatures have been declining, the left blame the La Nina effect, say that it’s only temporary and that La Nina is OK because it’s “natural”......
I actually had this conversation this morning with a liberal who also thought Jimmy carter was one of our best presidents.....
Well presented article.
Too bad the diagrams aren’t appearing.
I have not read anything to date about what the greenhouse effect would look like. Knowing that what is in fact going on is nothing like what the greenhouse theory predicts is a rather large nail in the coffin of manmade global warming hysteria.
Beautifuly written, outstanding article, and your logic seems impeccable. Unforntunately, the Goreons will never read it.
Cock crows, sun rises. Ergo Cock caused sun to rise. WRONG. Dead wrong. And very expensive to believe.
I did that purposely, because the images are all on my personal web space and I don't know how much bandwidth I'm allowed to take.
For images, just click on one of the links at the beginning of the post for either an html or pdf version with all the pictures.
This is a very good article.
FWIW I made that determination before I discovered that you were the author.
Upload your images here and then link them to the article.
Just last night the PBS station had a series on the history of India. Seems many of the large cities disappeared due to “global warming”, way back around 1500 B.C. (NOT BCE!).
How many cars were driving then?
Look to the nearest nuclear furnace to Earth, a star, some call it the “Sun”. Tell me about the spike in temperature, or decrease in sunspot activity.
Polar ice caps melting? Happens on Mars!
I could go on, but thanks,
“temperature and Earth’s orbital variations.”????
read about that here:
What causes the Earths climate to change?
Climate change is complexthere are many dynamics involved. A major factor may be the relationship between the Earth and the Sun.
Astronomer Milutin Milankovitch (1879 1958) studied the variations in the shape of the Earths orbit around the Sun and the tilt of the Earths axis. He theorized that these cyclical changes and the interactions among them were responsible for long-term climate changes.
Milankovitch studied three factors:
1. Changes in the tilt of the Earths axis;
2. Variations in the shape of the Earths orbit around the Sun; and
3. Precession: changes in how the tilt of the axis is oriented in relation to the orbit.
Hmmmm, lesseeeeee......I’ll makes this simple so Obama can understand it (e.g., no math).
Global warming has occurred N times (where N is a large number).
N-1 of these times were way, way before cars, etc.
N-2 of these times were before humans.
Ergo: (OK, Obamaloon, let’s see if you can figure this one out.)
Actually, it’s a superlatively-presented article, well worth reading the pdf version to see it diagrams and all. It presumes no prior knowledge of climate science, but explains succinctly and most persuasively why, as the author concludes: “Only irrational logic could support such a choice.” I’m not sure why this last sentence was stripped from the html version posted above.
I live within a very large Superfund Site. The EPA has been present here for over two decades. They have very seriously adversely impacted the local economy and business climate. The local folks would like to be rid or their "help." Early on a "Science Committee" of some very talented local citizens was established to refute some of the claims made by the EPA.
At a meeting of local (Science Committee), state and EPA people some very compelling evidence was presented, accepted and subsequently implemented into future Superfund projects. Not the local one. We are still stuck with EPA regardless of the facts. One of the state people at that meeting said, privately to a Science Committee member, that the situation is not one of science, but it is political. No matter what we did or will do, we locals will not win the argument on science or logic.
pjd has presented a very good article. Had I not already been convinced, this would have done it. Now this reasoning needs to be incorporated into the political argument. That is where the algores will be defeated. Not on evidence alone.
Bump to save
Outstanding article, IMHO! Thanks!!