"Here. Have a video. Evidence of global warming. Science win!" And around we go again, as if repeating things often enough, or merely calling it "science", establishes truth. A fisking is in order.

Fisking is the refutation of an article (or in this case, video) on a point by point basis. The term, coined in the pre-history of blogging, is derived from the name of journalist Robert Fisk, whose writing presents a particularly soft target for such treatment. Luckily, Fisk says doesn't read the internet, so it doesn't bother him that half the world shreds his articles for entertainment.

Here is the video in question:

It was made by James L. Powell, an "author, scientists and non-profit executive", who is about to publish a book entitled, "The Inquisition of Climate Science". I can't wait to buy it, if only for the photos of torture and executions.

The video's tagline says, "Is global warming true? Look at the evidence and decide for yourself."

So, let's look at it.

From its first words, the film is disingenuous. It implies that sceptics deny that global warming is happening, that humans are the cause, and that it's dangerous. Truth is, most accept the first, question the extent of the second and doubt the last assertion.

Most sceptics accept that the 40-year (and 100-year, and 300-year) temperature trend is rising. However, they doubt the accuracy of the data, that this is "warming on an unprecedented scale", that human activity is the most important cause, that the future has only warming in store, and that this would involve only dangers. They also question the motives of climate scientists and the green industries that have grown up around them.

That may be why the film has to appeal to Sudan and Zimbabwe to make up the rather low number of 33 national science academies that support man-made global warming claims. Besides, they're government institutions, so they're not exactly unbiased in this matter. Colour me sceptical.

The hardly-legible list of organisations that believe "global warming is true" includes several outfits that were founded on this explicit presumption. Some are outright political lobby groups. Agreed, however, that few, if any, organisations of scientists in the world say "global warming is not true". But neither do most serious sceptics, if that's how you're phrasing the question.

Then we get to "climate scientists". This is a self-selected group, of course. They are predisposed to claim that climate change constitutes a crisis. If you were a bright kid with a bent for mathematics and science and you had to choose a field of specialisation, but you didn't think climate change is a crisis, and it would be worth building a career to study this field, wouldn't you rather be a physicist, or a molecular biologist, or a statistician, or a genetics researcher, or a mechanical engineer? Would you devote your life to a field in which you don't already believe? Aren't you likely, once you've chosen a field, to defend its raison d'etre against all comers?

Why insist on this narrow definition of scientists eligible to theorise on the subject of climate change? The earth's climate is a vast, complex system, and requires a wide-ranging, multidisciplinary research approach, so why quote only scientists who have signalled their preconceived ideas by defining their field so narrowly?

This does not mean there's a conspiracy. Alarmists often use this dismissive term to discredit the idea that the global warming lobby argues its own vested interests. It isn't a conspiracy that all shopkeepers in a town try to make a profit and promote the virtues of shopping, either, but they do all act alike. All act independently in their own interest, just like climate scientists do. Billions of dollars worth of research grants – whole institutions and entire careers – are dependent on the notion that global warming is a crisis that needs our urgent attention.

That's not to mention the corporate interests in green technology, of which Al Gore's Generation Investment Management is merely one high-profile example. Billions of dollars in speculative investments are at risk. All of these investors would greatly benefit from environmental regulation and subsidies, while many would stand to lose their shirts if climate change didn't turn out to be a grave crisis. Again, this does not constitute a conspiracy theory. This is merely how companies operate: each independently seeks the advancement of its own interests, and tries to lobby government to pass laws that benefit them and disadvantage their competitors.

That climate scientists say climate change is a crisis is like quoting priests on the evil of sin. Most would claim there's too much of it about. That green technology companies agree is like asking wealthy televangelists for a second opinion.

So far, we have only transparent rhetoric, full of appeals to authority and consensus, neither of which constitute "evidence".

The film continues equally disingenuously, with a primary-school lesson on the greenhouse effect. Does he mean to imply sceptics dispute the existence of the greenhouse effect? Surely not. Sceptics are far more likely to argue that more CO2 in the atmosphere has a progressively smaller impact on warming. Or that there have been times when CO2 concentrations were many times greater than they are today, yet this did not result in runaway global warming, which prospect alarmists now warn is very possible.

Moreover, sceptics claim there are other greenhouse gases that are far more abundant and influential than CO2, not least of which is good old water. In fact, humans contribute only about 0.3% of the total greenhouse gasses in the atmosphere. The behaviour of water in the atmosphere, and in particular the effect of cloud formation, is not at all well understood. In all, they conclude that there is scant cause for believing that human activity is the primary cause of global warming.

Sceptics are also worried by chart manipulation. Take the triple-chart that anchors the video. The scales for the three overlaid elements are arbitrary. They are chosen to make them look like perfect matches. Most glaring is that each scale has a different base (only one of which is zero), and measures in different units. This is a classic trick in the arsenal of those who manipulate statistics to make a political point, and makes whatever follows appear suspicious.

Even the temperature chart itself suffers from this scale problem. It is the Michael Mann hockey stick chart, the most widely-promoted "evidence" that 20th-century global warming is unprecedented. It has been convincingly debunked by Ross McKitrick and Steve McIntyre, but keeps cropping up. Instead of using the same proxy data (tree rings) for the entire chart, it switches to instrument measurements around 1960. Where they overlap, they disagree. However, scientists appear to simply ignore that contradiction, instead of wondering whether the tree ring data in question – data which has itself been challenged because of highly selective sampling – is a good proxy for temperature. Even if it were, there is no way of determining the proper scale for the proxy series, so it cannot be compared to the instrumental series in order to deduce a trend. The same problem appears in the subsequent charts, where ice cores and other proxies are used for the historic temperature record.

It would have been nice to have a modern thermometer planted in the middle of the Little Ice Age or the Medieval Warm Period to add scale to the proxy data. Without it, sceptics question whether it is possible to draw firm conclusions from a comparison of historic proxy data with contemporary temperature data. Maybe it once was warmer, maybe not. We cannot say.

This is a basic scientific error, so the continued insistence that the hockey stick chart is credible can only be attributed to a desire to perpetuate a false result.

Even if the scale of the two series is correct, the scale of the overall chart has been chosen to exaggerate 20th-century warming. It doesn't, for example, show clearly that there was significant variability throughout the century, with a 30-year decline sandwiched between two rising trends, despite our CO2 output rising consistently.

Nor does it show that the 1998 high was in the continental US at least, comparable to the highs of the 1930s dustbowl years, or that the charts show a decade-long plateau since then that may well signal a trend reversal. This oddity is not addressed at all in the video. Warmists explain it away by attributing the 1998 peak in temperatures, which used to be cited as "evidence" of global warming, to a particularly strong El Niño. Such inconsistencies undermine the narrative of exceptional, man-made, runaway warming, so it is dangerous to show them if you're asking viewers to make up their own minds.

Sceptics are also wary of cause-and-effect assertions, when data merely seems to be correlated. There's some clever rhetoric in the video about this problem. If you don't believe the chart shows cause and effect, the narrator says, you have to accept two things we don't know. Note that they are not two things we know to be false, and in fact, neither are particularly implausible. Moreover, we do not know the alternative to be true. The entirety of his argument is: just accept it, because we can't think of anything else. Scientists once accepted all sorts of strange untruths on this basis.

By contrast, we do have reason to suspect that the cause-and-effect explanation has some holes. Historically, for example, temperature trends appear to precede changes in CO2 concentrations by several centuries. This is a fact that Al Gore, in his film, An Inconvenient Truth, found too inconvenient to mention. He glossed over it by calling it "complicated".

No surprise. If true, this fact – like a few others that are too inconvenient to be covered in the video – would conclusively scupper the entire theory of CO2-induced global warming, all by itself.

The observation does supports some alternative theories, however, such as those involving oceans as heat sinks and stores of CO2. Of course, this would mean finding an alternative cause for temperature changes, too. One candidate is the effect of solar activity upon our atmosphere. Effects are not limited to direct heat output irradiating the earth, but also how its changing magnetic field affects cosmic rays, which influence events in the atmosphere such as rain and ice formation.

Unlike warmists, sceptics do not claim such theories as proven truth, just because they seem plausible and explain a lot. However, there is at least as much correlative "evidence" for them, and they have the great advantage that temperature changes occur a few decades after the apparent cause, rather than before it. Ironically, this is also the rather weak basis upon which warmists dismiss this theory: a lack of correlation over just the last three decades, which happens to equal the observed lag between cause and effect.

This guy does worse, however. He avoids any explanation of the solar variation theory, dismissing it brusquely: nights have warmed more than days. Citing this as a falsification of solar theories of climate change stretches credulity.

One of the pieces of "evidence", regarding oceans having warmed steadily since 1970, actually contradicts the theory of man-made global warming. Ocean temperature changes happen on long time-scales, so their warming is unlikely to have been caused by industrial activity of the last half-century. They are more likely a cause of global warming, than an effect.

The video then goes into a long list of apparent effects of warming. Since the warming trend itself is not in dispute (depending on the date range under consideration), neither are these effects.

Observe some curious anomalies, however: in the 1970s, it appears a lot more glaciers than usual were advancing, and fewer were retreating. Why, if temperatures were rising? And if the temperature has been rising until 1940, declining until 1970, and rising most precipitously since then, why has sea level rise been so consistent, since before we began to emit a lot of CO2? And where are the metre-scale rises that threaten to inundate entire countries?

None of these charts are relevant to the argument, however, so it is not worth wasting time on them. Presenting such observations is merely another neat rhetorical trick to distract from the real issue: does human activity causes temperature changes, should we expect warming to continue, and if it does, will it reach disastrous levels?

And with that, we have reached the end of the "evidence".

None of it addresses the issues that sceptics raise: that the anthropogenic contribution to warming is speculative and exaggerated, while natural causes are played down; that computer models are inconsistent, contain built-in assumptions about "forcing" to make them fit predetermined conclusions, and fall far short of adequately modelling the atmosphere and oceans; that measurement networks are patchy, inaccurate in many cases, and the actual data is a disorganised mess; that scientists are well aware that some climate research relies on selective and incomplete data; that measures proposed to curb warming will be extremely costly and will be surprisingly ineffective; that there are better ways of investing these resources.

And all of this, before we add the Climategate revelations, which, as I've written before, fell short of proving scientific fraud, but did show gross incompetence in handling the large datasets involved, the use of clever tricks instead of sceptical inquiry to varnish over inconsistencies, disregard for both law and the public interest in handling information that is being used to justify far-reaching policy measures, and active efforts to subvert the peer-review mechanism to exclude legitimate science that contradicts man-made global warming theory.

This isn't a plot, or a conspiracy theory. This is simply bad science, conducted by scientists whose careers are on the line, paid for by investors with a stake in the outcome and politicians who want the moral cloak of playing saviour in a crisis.

Clinging to received dogma, by repeating hoary arguments unilluminated by new facts, demonstrates an abdication of critical thought that is not conducive to credible science.