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Believers and Skeptics
Global warming is a vital public issue about which there are many misconceptions. Most of the media oversimplify and classify scientists into two camps: "Believers" who are convinced not just that global temperatures are rising but that human use of fossil fuels is responsible; and "Skeptics," most of whom accept that global temperatures are rising but believe it is a natural fluctuation in climate with a minor or negligible effect from human activity. The purpose of this web page is to argue the "Believer" case while at the same time arguing for a sharp reduction of fossil fuel not just because climate is adversely affected, but equally important because of the need to reduce pollution and international conflicts. It is also important to counter some of the flimsier skeptic arguments, especially those that are dressed up in academic garb so as to confuse not just the general public, but serious scientists as well.
A Global Warming slide show
I have prepared a slide show to explain some of the intricacies of global warming, what can be done about it, and why it is necessary to act now. My approach is unique: I have reviewed some of the major challenges to global warming science over the past century or so, including a number of recent ones. My review shows that resolutions of the challenges have inevitably come down in favor of the existence of global warming caused by human use of fossil fuels.
Click on the following link to download a copy of the slideshow:
To put my counterargument to the skeptics in a nutshell, it is much more difficult to demonstrate that the increase of carbon dioxide (CO2) from fossil fuel useover the past 150 years or so did not have a significant effect on global climate than it is to show that it must have a significant effect.
Serious study of the impact of human activity on global climate requires an arsenal interdisciplinary science, and the issue must be pursued over a long period of time. Global warming science on a big scale began only in the late 1980s and is much more developed now, even though much remains to be done. After reading many scientific papers on the subject and doing my own study of radiation transfer theory and observational data, I am convinced that the scientific effort brought to bear on the problem leads to the firm conclusion that human emissions of greenhouse gases (GHG) are indeed causing global temperatures to rise. (A personal note: when I say “firm” I mean that I am about 90% confident of that conclusion.)
Despite the great effort required to scientifically conclude that human activity is inducing global warming, it is, as I mentioned, much, much more difficult (I would say impossible) to arrive at the opposite conclusion: that a 35% increase in CO2 (from a historical 280 ppm to today’s more than 380 ppm), and significant increases in other greenhouse gases associated with human activity, have little or no effect on global temperature. To understand why, a few central facts of about our planet’s temperature must be understood.
If average global temperature is to be more or less constant within a few degrees (as we observe it to be), solar energy input to Earth (“insolation”) must be balanced by an equal emission of energy from Earth to space. That is, Earth must be in thermal equilibrium with its spatial surroundings, of which the sun is by far the most important actor compared to our very distant cosmic neighbors. But if you look at Earth from outer space, you reach a strange conclusion: Earth’s average temperature is about –18 deg Celsius, i.e., about –0.4 deg F. This value is very easily obtained theoretically from the Stefan-Boltzmann radiation law, assuming an energy input from the sun of about 1370 watts per square meter, and an “albedo” (i.e., a reflection coefficient) for Earth of about 30%. If this were the average surfacetemperature of Earth, life as we know it would be impossible. Actually, if Earth’s temperature were –18C, the temperature would drop even further because a temperature of –18C itself would cause freezing of all lakes on Earth, which would cause more sunlight to be reflected (i.e., the albedo would increase), and after the resulting additional temperature decrease, much of the oceans would then freeze leading to more reflection and additional temperature decrease, etc., etc. Life would probably be impossible.
Now in fact, the average surface temperature of Earth has historically been about +14C (57F), which is nice and comfortable for life as we know it. If Earth is –18C from outer space, why is it about 32C warmer on the surface? Because natural GHG, especially water vapor and CO2, act like a blanket to keep the surface and lower levels of the atmosphere levels warmer.
(You might ask how Earth’s surface can be so much warmer than Earth as seen from outer space. Our perspective is distorted by the fact that the human eye can see only a very small part of the electromagnetic spectrum, so from a satellite, astronauts see only the visible radiation reflected, not emitted, by Earth. The infrared radiation emitted by the stratosphere, lower layers of Earth’s atmosphere, and Earth’s surface is invisible to the human eye. In fact, a view of Earth’s emissions by an organism with eyes sensitive to all wavelengths of the electromagnetic spectrum would show almost no visible light. From outer space, a good bit of the emitted radiation is from the cold upper regions of Earth’s atmosphere, and the overall emission is characterized by a temperature of -18C.)
The great difficulty for skeptics is to look at the warming effects of various GHG. A reliable estimate shows that water vapor warms Earth’s average temperature by about 21C, which would bring it up to 3C (36F), barely above the freezing point of water. The rest of the warming necessary for life as we know it comes from CO2, which reliably warms Earth an extra 7C or so, to about 10C (50F). The remaining 4C (7.2F) comes from other natural GHG such as methane, ozone, and nitrous oxide. Given these facts, it is hard to believe that a 35% human-caused increase over the natural level in such an important GHG as CO2 wouldn’t have a significant effect on Earth’s temperature.
The issue is a bit more complicated than I’ve just outlined, because the climate system is highly “non-linear,” meaning that the net effect of various GHG is not simply the sum of the effects which would occur from each GHG separately. But the concrete fact that must be faced by the skeptics is that water vapor, the most voluminous GHG, cannot by itself warm Earth to its present toasty temperature; CO2 plays a crucial role, amounting to about 22% of the total warming. The skeptic belief that Earth’s temperature wouldn’t be seriously affected by an additional 35% increase of this very important GHG is physically inconceivable.
The skeptic challenge on cycles
Despite the wealth of corroborative evidence pointing to CO2 as the causative agent responsible for the rise in temperature over the past 150 years or so, the main skeptic claim is that we are experiencing a natural cyclical change. Looking at Earth’s temperature over thousands of years, there is general agreement that “Milankovitch cycles” involving Earth’s orbital parameters (ellipticity of the orbit, tilt of rotational axis, and wobbling of the axis, better known as “precession”) have a quite pronounced effect on global climate and are primarily (though not solely) responsible for ice ages. But such long cycles are irrelevant to the rapid changes we see today. But there are a host of other cyclical patterns discernable from the ancient temperature record (as constructed from isotope analysis of ice core bubbles, from sediment composition, etc.) which disclose short cycles, all the way down to the el Nino-la Nina 4-5 year cycle. Many of these cycles arise from the internal dynamics of the climate system. An interesting one is the hypothetical Gleissberg cycle of about 80 years.
Cycles just go up and down with no trend over the long run, i.e., the ups are canceled by the downs and vice versa. The signature of global warming is a combination of cyclical swings with an overall upward trend over the long term, so the downs do not completely cancel out the ups. This upward trend is correlated with increases in human-produced GHG. Assuming the Gleissberg cycle is for real, then the rapid increase in temperature from about 1900 to 1940 was a combination of the upward part of the cycle plus an additional upward push from emission of human-produced GHG from fossil fuels. The downward part expected over the next 40 years or so would normally cause global temperature to decrease, but from 1940 to 1979, we saw only a leveling off of global temperature (or at most an insignificant decrease), followed by an even greater increase from 1979 to the present which was more rapid than the 1900-1940 increase. This behavior indicates a mix of an up-and-down cycle with an upward trend, apparently caused by fossil fuel use that was strong enough to cancel out the natural down part of the cycle from 1940-1979.
As any student of time series knows, white noise includes all frequencies. The climate record prior to industrialization is not quite white, and is not quite stable either. There are a host of complicated historical/accidental factors, such as the closing of the Isthmus of Panama which greatly reduced the interaction between Atlantic and Pacific oceans, and volcanic activity, which are random in nature and muddy the water so to speak. There are also a host of complicated “endogenous” feedback factors, particularly the melting or freezing of ice caps and ice sheets which change Earth’s albedo and cause additional temperature change. A mathematical (or "Fourier") analysis of the temperature time series shows strong signals at the Milankovitch frequencies, and the same can be said for a number of other lower frequencies. It is not clear how important a persistent Gleissberg frequency is, but it is certainly not negligible. Again, the fact that the downward part of this latest cycle appears to be largely negated by a rising trend in temperature is very significant and worrisome. CONCLUSION: the current rapid warming does not appear to be cyclical. Instead, the underlying cyclical pattern of temperature is being uplifted by a constantly-increasing upward temperature trend.
The skeptic challenge on climate models
Climate models are used to predict the future impact of fossil fuel burning. Such models are important, even vital, but they have been subjected to trenchant criticism by skeptics. Skeptics make the obvious point that models are uncertain in their estimates of future warming. What they fail to point out is that uncertainty cuts both ways: the future could less warm than the models predict, but it might also be warmer. The importance of models in global warming science shouldn't be overemphasized. My argument above regarding the warming effect of CO2 is based on laboratory measurements of the spectral properties of the CO2 molecule that are quite precise and have nothing to do with the models that vex skeptics. These spectral properties and direct measurements of CO2 concentration in the atmosphere provide a more firm basis for concern about global warming than anything a model has produced. As imperfect as climate models are, they are a tool that must be used. All the climate models I’m familiar with use proven statistical techniques to quantify uncertainty in estimates As mentioned, it is important to remember that uncertainty cuts both ways: maybe we’ll end up on the lower end of model-guided estimates of global temperature, as skeptics seem to wish, or we could end up on the higher end, in which case we’re in for serious problems. Prudence suggests that we clean up our act, especially since there are valuable payoffs, such as a reduction in global tensions in the mad scramble for scarce fossil fuels and improved air quality, even if human-induced global warming is not a great worry.
The most important skeptic error
Skeptics argue that rising CO2 is only correlated with increased warming, i.e., the real cause is natural factors other than CO2 which just happens to increase with temperature. By "natural factors" is meant such things as solar activity or changes in Earth's orbit that have nothing to do with human use of fossil fuels. Many of the skeptic arguments are based on the straw man argument that global warming believers believe and must show that all warming throughout climate history has been caused by "demon CO2." No serious climatologist believes that. It is universally recognized that climate depends on Earth's orbit, volcanic activity, solar activity, and a host of internal cyclical processes in Earth's oceans and atmosphere. The challenge is to disentangle the various factors from each other, a task that skeptics really do not wish to engage in not just because it is so difficult to do so, but also because they don't think it is important.
Here is a prime example of the skeptic use of the "everything must depend on CO2" straw man. In the 1990s, evidence was gathered showing that recoveries from ice age cycles thousands of years ago showed that the recovery from cold temperatures began about 800 years on average before atmospheric CO2 started to rise. This prompts skeptics to issue this challenge: "Ah ha, see, CO2 was not responsible for past rises in Earth's temperature. So why assume it is now?" But no climatologist ever said it is always responsible. What climatologists do believe is that CO2 is responsible now, because: (1) CO2 has the physical properties it has--it is transparent to visible light and absorbs infrared light; (2) other factors such as solar and volcanic activity are not sufficient to explain the warming we are currently experiencing; and (3) CO2 is rapidly increasing in the atmosphere. It still remains to explain why was there an 800-year lag between recovery from an ice age and an increase in CO2. The explanation is very simple. Up until the 20th century, recoveries from ice ages were caused primarily by other factors such as changes in Earth's orbit. When these other factors succeeded in raising the temperature of Earth's oceans (which tend to change slowly), the oceans are not able to hold as much CO2. (Example from everyday life: if you open a bottle of soda and want it to stay carbonated, keep it cold; if it warms up, most of the CO2 comes out.) So as the oceans slowly warm up, CO2 is released after a longer period of time--about 800 years. Of course, once the CO2 content of the atmosphere increases, this just adds to the heating initiated by other factors. The scenario described shows CO2 as a feedback effect, following on the initial warming effect from changes in Earth's orbit, and/or increase in solar activity,...etc. In such a case, the oceans become less acidic. But today, we are observing just the opposite. CO2 is increasing in the atmosphere because of fossil fuel use, and this is the primary cause of the warming. Consequently, although the oceans are warming, there is so much CO2 in the atmosphere that it seeps into the oceans making them more acidic. The acidic content of the oceans has been measured many times, and there is no doubt it is becoming more acidic. So unlike previous warmings of Earth, which decreased the oceanic acidity, the acidity is now increasing.
The Infamous Skeptic Petition Project
Frederick Seitz was a famous physicist who in 1940 wrote a widely influential text book, The Modern Theory of Solids, which could still be read with profit by students today. Seitz had an illustrious career, including president of Rockefeller University and president of the National Academy of Sciences. Later in his long (97-year) life, Seitz worked for tobacco companies, and also became a vocal critic of anthropogenic global warming. Seitz was instrumental in organizing a petition project to enlist names of "scientists" on a petition calling for the US government to resist efforts to curtail use of fossil fuels. I use scare quotes on "scientists" because there is no evidence that all of the signatories on the petition were natural scientists or even social scientists.
The petition was surface-mailed to thousands of scientists and other academics around the country, and was accompanied by what appeared to be a serious article from a refereed journal titled "Environmental Effects of Increased Atmospheric Carbon Dioxide." Indeed, the format of the article suggested it had been published in the highly-regarded Proceedings of the National Academy of Sciences, which would mean that it had undergone serious review. The authors of the article were Arthur Robinson, Noah Robinson, and Willie Soon, abbreviated RRS in what follows. It is unclear what credentials the Robinsons have, but Soon is an astrophysicist at Harvard--not a climatologist.
Go to this link for a history of the project and a statement of the petition:
Go to this link for a copy of the RRS article:
A detailed critique of the RRS paper
The latest and largest reincarnation of the petition project was in 2007 when the petition, accompanied by the RRS article, was sent out to many thousands of academics. I received a copy by US mail, as did several of my colleagues at Roanoke College. Shortly after, I attended a meeting of physics teachers and was taken aback that there was genuine interest in the article, thinking it was serious science. This prompted me to carry out a full-scale review of the RRS article, which can be downloaded at this link:
A copy of my detailed critique of the paper can be downloaded at: