A politically liberal global-warming skeptic?

There is no doubt that human-caused production of carbon dioxide is adding appreciably to the rate at which the Earth is warming. That’s settled science.
At least so it’s said by commentators on MSNBC, on PBS, and in most of the other media.

There is no proof that carbon dioxide is causing global warming.
At least that’s been said by prominent Republican candidates for President of the United States, and by commentators on Fox News and other conservative media.

It is politically incorrect for people on the political left to doubt human-caused global warming. It is politically incorrect for people on the political right to accept human-caused global warming. In other words, beliefs over a matter of supposed scientific fact are determined by political ideology.
This is absurd, yet the absurdity is being largely ignored in public discourse.

This state of affairs comes about in some part because science is thought to be too technical for the general public to understand. So the matter is left to be settled by science itself.
But what is science itself?
The conventional wisdom equates it with the position taken publicly by scientific organizations and their representatives — what’s often called the mainstream consensus.

Could the mainstream consensus —  “science itself” — ever be wrong?

Historians of science would find it hard to take that question seriously. They know that in one sense the mainstream consensus has always been wrong, at least in the long run. To varying degrees, of course; sometimes only a little wrong, but also sometimes entirely wrong. Science has progressed because the mainstream consensus at any given time was never the last word.
Around the beginning of the 20th century, quite a number of mainstream beliefs turned out to have been completely off the mark: unstable atoms, radioactivity, particles as waves and vice versa, energy existing as bundles and not in arbitrary amounts . . . .
Is all that water under the bridge? Is science now on the right path everywhere? Has the mainstream consensus somehow become the last word now?
Believe that at your peril. As the saying goes, those who do not remember history are doomed to repeat it.
But who remembers the history of science? Only a few historians and specialists in science & technology studies (STS), a relatively new field that seeks to integrate history of science, philosophy of science, sociology of science and other pertinent disciplines.
Concerning the possibility that a present-day scientific consensus could be wrong, the conventional wisdom, the media, the contemporary scientific authorities all seem to be ignorant of history. So we keep repeating that history of dismissing and deriding minority opinions, some of which later turn out to have been more correct than the mainstream. For one instance, Drs. Barry Marshall and Robin Warren discovered the ulcer-causing bacteria, Helicobacter pylori, in 1982, but they were ignored, dismissed, derided by the mainstream consensus for a decade or two, because everyone knew that ulcers were caused by stomach acid and emotional stress; still, in 2005 Marshall and Warren received a Nobel Prize for their discovery. For another instance, recall that Carleton Gajdusek received a Nobel Prize in 1976 for discovering that kuru-type brain diseases (akin to mad-cow disease) were caused by a “slow virus”; but in 1997 Stanley Prusiner received the Nobel Prize for discovering that those brain diseases were caused by mis-shaped proteins, prions, and not by a virus. For an entrée into the literature about mainstream opposition to novel views, try Ernest Hook (ed.), Prematurity in Scientific Discovery: On Resistance and  Neglect, University of California Press, 2002.

In principle, then, any scientific consensus could be wrong. How are the media, the public, the policy makers to judge, whether or not a given consensus is to be believed? Believed firmly enough to base on it such policies as attempting to curb emission of carbon dioxide, at enormous cost and disruption of industries?
Roger Pielke, in The Honest Broker (Cambridge University Press, 2007), suggests that the proper role for scientists is to lay out all sides of any given question and not to claim 100% certainty for any finding or theory. But that is far from the general practice. With global warming, for example, the policy makers and the media and the general public hear much about the scientific consensus and almost nothing about those who dissent from it — except that those dissenters are maligned as “denialists”, a conscious analogy to those who deny that the Holocaust happened, the Nazis’ deliberate extermination of Jews, Gypsies, homosexuals, physically handicapped people, and others as well.
In absence of historical understanding, the fact of an existing consensus is said to establish its correctness. In the FRONTLINE documentary, “Climate of Doubt” (PBS TV, Tuesday 23 October 2012), the presenter (John Hockenberry) mentions several times that 97% of scientists accept that carbon dioxide significantly contributes to present warming — says it as though that discredits the skeptics whom he interviewed.
There are two improper things about Hockenberry’s 97%. One is that it merely states that a consensus exists, when there is no guarantee that a consensus is necessarily correct. But it is also improper to assert dogmatically on a matter of science something that cannot possibly be based on known fact: Did Hockenberry ask all scientists before arriving at that “97%”?
As to consensus, be it 97% or anything else, it’s hard to beat Michael Crichton’s take:
“I regard consensus science as an extremely pernicious development that ought to be stopped cold in its tracks. Historically, the claim of consensus has been the first refuge of scoundrels; it is a way to avoid debate by claiming that the matter is already settled. Whenever you hear the consensus of scientists agrees on something or other, reach for your wallet, because you’re being had” (“Aliens cause global warming”, Caltech Michelin Lecture, 17 January 2003; Google can find links to transcripts of the whole talk).

How then might a lay person reach a reasonable opinion on a scientific matter like global warming where there is a sharp, politically determined polarization between a mainstream consensus and a dissenting minority?
Only by looking at the evidence, of course.
But could non-specialists make head or tail of the evidence? Isn’t it all too technical for a non-specialist?
Not at all. There are several easily understood points to guide the reaching of a reasonably informed opinion:
1.    Do any competent scientists disagree with the mainstream?
If they do, then this might be one of the cases where the mainstream is wrong. Even 100% agreement doesn’t guarantee that the mainstream view is the last word, so history tells us; still less is 97% when the dissenting view is held by some of the most competent experts. In the case of global warming, there are thousands of dissenters; see for example the Leipzig Declaration and the websites of Fred Singer (www.sepp.org) and Roger Pielke Sr. (pielkeclimatesci.wordpress.com). For continuing coverage of news and controversy, try wattsupwiththat.com.
2.     What evidence could support unequivocally the mainstream opinion?
Note first that the crux of the mainstream view is a prediction more than a statement of observations already made. After all, even if there has been warming for some period of time, that does not entail that the warming will continue. Even if warming and carbon-dioxide levels have increased in tandem, that is only a correlation and not any proof of causation: correlations never prove causation.
To assess the possible effect of carbon dioxide on future global warming, one would need to take into account everything that influences the heat balance of the Earth. Even cursory scanning of the literature reveals quickly that there are innumerable relevant factors. The rate at which the sun radiates energy to the Earth, for example. The greenhouse effect — trapping of energy by gases in the atmosphere — is brought about not only by carbon dioxide: water vapor is actually responsible for more of the greenhouse effect than is carbon dioxide, about 3 times as much, in fact; methane is responsible for about as much greenhouse action as is carbon dioxide, at present levels of both. Heat also comes to the Earth’s surface from below, illustrated by the lava or magma flows from volcanoes and deep-sea rifts. An excruciatingly detailed and documented enumeration of factors can be found in Ian Plimer’s Heaven and Earth: Global Warming, the Missing Science (Taylor Trade Publishing, 2009).
3.    The upshot is that the possible effect of carbon dioxide on global warming cannot be calculated directly. Instead, a model is constructed of the Earth’s climate. But the model can be trustworthy only if it incorporates every pertinent factor. With so many factors involved, one can be reasonably sure that no model could be absolutely reliable. Even if all the influences were known, one would also need to understand exactly how they interact with one another. For example, the largest greenhouse effect is owing to water vapor, and the amount of that in the atmosphere varies with temperature (among other things). Cloud formation depends on the amount of water vapor as well as on other things (e.g. radiation and presence of material particles that act as seeds on which water vapor can accumulate); and clouds may add to or subtract from global warming depending on how high they are, as well as on other factors.
4.    Most damaging to any mainstream modeling is the fact that the Earth’s climate has undergone many cycles of temperature, over ranges of temperature far larger than those currently being measured or calculated or speculated about. Over the Earth’s known history, average temperatures have cycled between about 10ºC and about 25ºC.

In the last million years, there have been 7 or 8 peaks and 7 or 8  valleys of temperature that differ by about 5ºC.

(Figures from Dogmatism  in Science and Medicine, where sources are given
Figure 1 has been turned by 90 degrees; click on it for a full-scale look)

The reason for those dramatic cycles is not known, or at least there is no agreement over what brought them about. Therefore no model of climate can be reliable, since it cannot account for these drastic historical variations in temperature.
5.    Finally: The last valley of temperature, the last Ice Age, came to an end only about 15,000 years ago. The historical cycles indicate that the Earth will now warm by about 5ºC over the next hundred thousand years or so owing to the influence of those unknown factors. It is impossible to stop that since we don’t understand why these cycles happen.

These points are surely accessible to anyone, and they demonstrate that one cannot truthfully claim that it is settled science, that human-caused emission of carbon dioxide is appreciably contributing to global warming.
There is no reason why conservatives should find these points more convincing than liberals do. As my title suggests, it is perfectly reasonable to be politically liberal and also skeptical about human-caused global warming. Indeed, I offer myself as an example.

Why have these points failed to penetrate public discourse?
I suggest the chief underlying reason is the failure to understand that mainstream science can be wrong. Such an understanding is an essential component of being literate about science. Scientific literacy ought to be defined — but presently is not — as literacy about the history of science and the nature of scientific activity and scientific institutions, not just literacy about bits of science like molecules or gravity.