(I ended up writing this as a lengthy answer to someone on Google+ — might as well let the world see it.)
Here’s what I’ve said so far:
“There are few skeptics (I can’t think of any, and I’ve been reporting on this for two solid years and an interested bystander for several years before that) who don’t believe there has been significant warming since the Little Ice Age, or that humans contribute to it, or that additional CO2 or other greenhouse gases aren’t probably part of that contribution.”
Unless one is arguing that humans are the only cause of global warming — in which case i’d have to point to that big glowing thing in the sky during the daytime — what I said explicitly includes a human contribution and even a greenhouse gas contribution.
Now, the IPCC AR4 model is rather stronger than that: it insists that anthropogenic, greenhouse-gas forced warming is the dominant — so dominant that it leads the unthoughtful to turn it into “only” — cause of global warming. For conciseness, call that the AGW model. Reasons I don’t find that hypotheses convincing include:
(1) from the start, it has depended on very sensitive statistical techniques to tease a signal out of an overall warming that has been going on for 500 years. Refer back to the famous “hockey stick” charts and then look for one with actual error bars: even in the papers making the strongest arguments for the AGW hypothesis have very wide error ranges — so wide that the AGW component barely exceeds the limits of the technique.
(2) the specific methods used for some of the dominant studies turn out to be mathematically flawed. in particular, the methods of Mann _et al_ turn out to present a clear hockey stick no matter what the input data is, including pure random numbers.
A method that detects a signal when there is no signal is necessarily suspect. At best.
Other examples of questionable parts of these results include:
- the methods used to select data points in the
GCHNGISS data sets — examined carefully, it turns out that the selected points used to compute GAST and regional temps are, to a *very* high probability, the points from the raw data set that lead to the most warming. Carefully read, the descriptions of the analysis even say that’s a selection criterion: they’re selecting data points that fit the models well — but then testing the models by how well they fit the data.
- actual site locations turn out to very commonly have poor site placement and site changes that would add significant warming. This warming has not be appropriately compensated for.
- odd ad hoc methods to fit together paleoclimate data and actual temperature measurement, including the famous “hide the decline” patching, and contrariwise the exclusion of recent tree ring data that suggests tree rings may not be as strongly correlated with temperature as we think. The explanations for those exclusions end up looking very ad hoc in themselves.
(3) There is actually extensive literature showing anthropogenic components that are not driven by greenhouse gases. These results have been excluded from the IPCC, often in very questionable ways (cf Roger Pielke Sr’s removal from the IPCC editorial board.)
(4) The predictions of further warming are necessarily based on models. Now, it happens I did my PhD work on Federally funded modeling, from which I developed the NBSR Law (named after the group for which I worked): All modeling efforts will inevitably converge on the result most likely to lead to further funding.
Anyone with a unbiased eye who looks into it will find any number of people who have found that a model that predicts more warming gets funded; a model that predicts relatively less warming gets less funding. Pre-tenure researchers in particular are warned away from results that don’t fit orthodoxy.
(5) The models themselves turn out not to be very predictive. Grossly, you could look at Jim Hansen’s prediction from the 80′s that Manhattan Island would be awash by the 2000′s. More technically, there were a number of models that predicted pretty significant warming, and in fact an increased warming rate, increased 2nd derivative, in the span 1990-2010. In fact, the warming was much smaller than predicted, and the second derivative appears even to have turned negative.
These models are often revised so that after the fact that predict what really happened. This isn’t very satisfactory.
In the mean time, actual observation, as eg with Dick Lindzen’s recent paper, simply isn’t fitting the models very well. As Granddaddy used to say “if the bird book and the bird disagree, believe the bird.”
(6) It’s unclear how the AGW hypothesis can be falsified in its current form. Certainly, anecdotally, there are people who predict that unusual warm spells are a sign of global warming, as are unusual cold spells. Should we have a period of unusually small variation, there are people who have suggested that as an effect of global warming. And in any case, simply observing warming doesn’t allow one to infer the truth of AGW as a hypothesis.
(7) The arguments against the skeptics turn out to be unscientific, and often unprofessional, in the extreme.
These range from the common — “the consensus is” — to the ad hominem, and even to outright attempts to suppress free inquiry.
“The consensus is” neglects the fact that science isn’t decided by consensus, not permanently at least. (At one time, the consensus was that fire involved a special elemental substance called phlogiston; at another, it was that atoms were indivisible and unchangeable; not so long ago, it was that light was a wave in a literally ethereal substance called the “luminiferous aether.” If consensus precluded further testing, we would still believe those today.)
The ad hominems include the way that anyone who ever received so much at a 10 cents off gas coupon from a service station is accused of being in the pay of Big Oil. Sometimes, the ad hominems are frank lies, but they get out into the AGW enthusiast community and are treated as truth.
And, well, anyone who read the ClimateGate files knows about actual attempts to suppress certain authors and papers. Perhaps it’s not fair to call it “conspiracy”, but the fact is that there is clear and unequivocal evidence of collusion and bullying on authors, reporters, and journal editorial boards.
If the AGW arguments are that strong, they don’t need collusion and bullying.
So, this is a very long piece considering I’m not getting paid to write it; let me summarize.
First of all, what *I* said wasn’t what you supposed I’d said. It would be worth considering what else you _think_ you’ve read recently for other cases.
Second, to the extent that I have a position, as I said, I think warming is unequivocal, a human contribution very probable, and the magnitude of that contribution in the face of feedbacks and homeostasis currently unknown and on the very edge of what we can actually measure.
And third, I don’t think the AGW enthusiasts consider the costs and benefits of AGW amelioration versus the other possibilities. If preventing a sea level rise of one meter means dooming future generations in the Third World to sickness, hunger, and darkness, it’s not worth it.