That's an important epistemological point to make. I guess we should all make our own GCMs to confirm for ourselves that we believe in AGW?? Sure maybe if we all had unlimited time. In science we share a common set of methodological beliefs and assumptions-- maybe there's a breakdown for her there, but I'd like to think the at the research institutions and tools that exist help accurately propagate true findings to the public especially in a matter that's as pressing to our long term wellbeing as climate change!
In the post below, her primary complaint about the 97% stat is that it doesn't specify the amount of climate change that those people attributed to humans: "After discarding the abstracts that were judged to have taken no position, Cook (2013) reported a 97% consensus that anthropogenic GHGs were causing global warming. However, three-fourths of that consensus was judged to be implied and more than 98% of the agreement was expressed non-quantitatively. Consequently, no widespread consensus exists in these abstracts that humans are responsible for most of the global warming; only that humans are responsible for an unspecified amount of global warming."
https://judithcurry.com/2015/12/20/what-is-there-a-97-consen...
I think the 97% stat provides a useful opportunity for those of us who would like to get to truth of the matter but haven't studied climatology and have no interest in spending years studying the subject just to determine the truth of this particular issue. So much of the argument about the subject is "they're wrong, I'm right" followed by technical explanation that you cannot tell who to trust. But you can understand how the 97% claim was reached. It provides a useful opportunity to gauge who to trust on the subject, although admittedly still requires careful consideration and more time that most will commit.
This John Stuart Mill quote seems apt: "People more happily situated, who sometimes hear their opinions disputed, and are not wholly unused to be set right when they are wrong, place the same unbounded reliance only on such of their opinions as are shared by all who surround them, or to whom they habitually defer: for in proportion to a man's want of confidence in his own solitary judgement, does he usually repose, with implicit trust, on the infallibility of "the world" in general. And the world, to each individual, means the part of it with which he comes in contact; his party, his sect, his church, his class of society: the man may be called, by comparison, almost liberal and large-minded to whom it means anything so comprehensive as his own country or his own age. Nor is his faith in his collective authority at all shaken by his being aware that other ages, countries, sects, churches, classes, and parties have thought, and even now think, the exact reverse. He develops upon his own world the responsibility of being in the right against the dissentient worlds of other people; and it never troubles him that mere accident has decided which of these numerous worlds is the object of his reliance, and that the same cause which make him a Churchman in London, would have made him a Buddhist or a Confucian in Pekin."
Ad hominem is an informal fallacy, not a logical fallacy. A logical fallacy always makes an argument invalid. An informal fallacy makes an argument extremely suspect, but context matters. Unless you can instantly read and criticize all the arguments published everyday, or unless you're immortal and don't care about timely application or responses to arguments, you must structure your approach to acquiring knowledge. Alternatively, you could go through life haphazardly, allowing coincidence or, more often, wealth and social station to dictate the ideas you're exposed to.
Your point would stand if climate skeptics were earnest and constructive participants. But they've shown themselves not to be.
In short, credibility matters. Climate skeptics as a group lack credibility, and climate skeptic arguments as a class lack prima facie credibility. In the context of climate change discourse, pointing out (with citation) that an author is a bone fide climate skeptic (a label and affiliation with substance in our times) is totally legitimate, IMO.
I appreciate that some people with idle time are willing to dive in and provide more substantive criticism. But such earnest people aren't always around, and even reading their analyses takes time. I think it's fair to argue credibility, just like it's fair to argue credibility wrt EmDrive without painstaking analysis of wild quantum mechanical hypotheses.
Many of the points she makes about statistical validity make sense - complex, non linear systems are difficult to predict, models need to be validated on data different from their training sets, etc. So those points, without digging into the real meat of how they're applied to these models specifically -- which she knows lawyers won't, serve to mislead.
I think what's also at the heart of this discussion though is whether what she's writing really is science or if it's opinion/has an agenda. When one puts oneself in the position of writing an overview like this, well then maybe it's one's responsibility to present (as well as complicate) the general consensus rather than present an argument that is not that mainstream as more of a consensus then it really is.
In fact, the opposite is true: it is skepticism of global warming that depends on the correctness of GCMs.
In the simplest model, which any kid can test in middle school, you take a plexiglass box full of air (representing the atmosphere), add some extra CO2 to it, and see if the temperature goes up. It does.
Well, since the mid-1800s, we have been adding CO2 to the atmosphere. We know that we've burned a lot of fossil fuels (that were underground), and we have directly measured an increase in the amount of CO2 in the atmosphere. So based on the simplest model, we'd expect to see the temperature going up. And we do! Yay, science works.
Of course there are a lot of ways to say that the simple model is wrong. But they all involve the construction of a more complex model. In order to see if anything will mitigate or compensate the basic physics of how more CO2 traps more heat, you have to add in additional factors.
So when someone goes on and on and on about the shortcomings of super-complex GCMs, remember this. GCMs are important tools for making detailed predictions and policy decisions, but we don't need them to predict the basic fact of global warming.
In fact the original hypothesis of global warming dates back to about 1900, well before anyone was using computers to model anything. The theory of global warming rests on basic thermodynamics, and it was first proposed not long after those basics were discovered.
The article does not discount the utility of GCMs in furthering our understanding of the climate in general, but reaches the conclusion that existing models are of limited utility when attempting to forecast the affect of policy changes (or the lack thereof) on climate trends.
What we don't understand (unless we decide GCMs are predictive and can be validated) is the impact of a given thermal forcing on planetary temperature. This is the "climate sensitivity." Unfortunately, this is the number we actually care about.
If climate sensitivity is low (negative feedback), Earth is thermally buffered and we have to worry less. If climate sensitivity is high (positive feedback), the opposite.
(Note also that Arrhenius, the discoverer of this effect, and pretty much everyone through the '60s, assumed that global warming was a positive side effect of burning fossil fuel, just from the preindustrial assumption that warm winters and high crop yields are good for humanity.)
In other words everything is very clear, it all adds up, it has added up and been clear since the early 1990s.
Basically "warming" in popular usage means "I can take my jacket off now", whereas warming in scientific usage means "increasing the heat energy stored in a given volume."
Scientists have known for a long time that global warming (increasing the heat stored in the atmosphere) would create both local heating in some areas and local cooling in others (it's chaotic). But when a regular person hears "warming" and then the temperature goes down, they're confused. Hence "climate change."
Incidentally, predicting the local effects of warming is a major goal of GCMs, and one for which no other tool will do. But it's damn hard (again: it's chaotic).
Looking her up afterwards, it seems to me that this may also be her push for a significant position in the Trump administration. Seems that Judith Curry is the scientist who says "Well, they've revised the likely range so clearly they don't know what's likely and maybe it's too expensive to do anything right now."
I won't bother linking, a simple search based on her name will turn up a wide variety of links to her history, people bemoaning her stances, and people refuting some of the arguments she uses.
The broad points about training data and non-linearities are important- but on a second pass it's hard to believe that people who spend their lives building GCMs don't think deeply about these challenges.
She cops a lot of flack and hysteria, just for raising reasonable doubts!
If climate science is solid, then it shouldn't feel the need to vilify anyone who questions it. If it isn't solid then it should be subject to as much scrutiny as possible given the derived policy will have tremendous impacts to life.
Perhaps the most balanced article easily found is this one from the commie pinko NPR: http://www.npr.org/2013/08/22/213894792/uncertain-science-ju...
Re: William M. Connolley, see https://en.wikipedia.org/wiki/William_Connolley as a starting point to differentiate from many others with slight name variations.
edit: link in the wrong place
My reading of the evidence suggests clearly that the IPCC conclusions are an accurate assessment of the issue. I have tried to follow the proposed logic of Judith’s points here, but unfortunately each one of these arguments is either based on a misunderstanding, an unfamiliarity with what is actually being done or is a red herring associated with shorter-term variability. If Judith is interested in why her arguments are not convincing to others, perhaps this can give her some clues.
http://webcache.googleusercontent.com/search?q=cache:pLrHr9q...
1) "If climate sensitivity is high, then we can expect substantial warming in the coming century as emissions continue to increase. If climate sensitivity is low, then future warming will be substantially lower."
2) "In fact, it seems that uncertainty about values of ECS has been increasing. The bottom of the ‘likely’ range has been lowered from 2 to 1.5oC in the AR5, whereas the AR4 stated that ECS is very unlikely to be less than 1.5oC. It is also significant that the AR5 does not cite a best estimate, whereas the AR4 cites a best estimate of 3oC. The stated reason for not citing a best estimate in the AR5 is the substantial discrepancy between observation-based estimates of ECS (lower), versus estimates from climate models (higher).
3) "If the climate sensitivity is on the low end of the range of estimates, and natural internal variability is on the strong side of the distribution of climate models, different conclusions are drawn about the relative importance of human causes to the 20th century warming."
4) "Whether or not human caused global warming is dangerous or not depends critically on whether the ECS value is closer to 1.5oC or 4.5oC."
5) "Given the uncertainties in equilibrium climate sensitivity and the magnitude and phasing of natural internal variability on decadal to century timescales, combined with the failure of climate models to explain the early 20th century warming and the mid-century cooling, I conclude that the climate models are not fit for the purpose of identifying with high confidence the proportional amount of natural versus human causes to the 20th century warming."
Is this an accurate summary of facts? Do we have good evidence about the true value of ECS that she does not mention? Is there evidence for scenarios where a 'low end' Equilibrium Climate Sensitivity still results in a dangerous warming? Or are there indeed values for ECS that would be considered 'likely' but do not result in dangerous warming?
Lack of knowledge about the true value of ECS is not an excuse to avoid precautionary measures, but it would seem to raise questions about the suitability of current climate models as predictors for future climate. At the least, it would imply that determining the true ECS should be a very high priority while other mitigation measures are taken.
That said, it's true that she does write elsewhere about her belief that uncertainty does not necessarily increase the urgency of action: https://judithcurry.com/2016/01/05/climate-models-and-precau.... I haven't read many of the linked posts, but it would seem fair to summarize her position as something like "we don't yet have sufficient understanding of the problem to justify taking actions that will cause definite harm".
Anyone can create a model that behaves consistently when it is trained on historical data to predict historical data.
How do they overcome the problem of overfitting and why should anyone have any confidence in it until it shows accuracy going forward?
That, and there are metric crap-tonnes of data to work with of all sorts. Just ungodly amounts of it.
Without any statistical treatment at all. And then later puts "expert opinion" of others in quotes.
At that point, I lost confidence in the analysis. Do some well known numerical and statistical tests of the models, and create a Bayesian based estimate based on all the models, and see where you end up instead!
It's unfortunate because climate change could be happening, but we aren't going to learn much more about it because research can't be invalidated. We've killed the skepticism science needs to function.
She's not denying it's happening, she's just not buying the grandiose narrative. I'm glad to hear her view, even just to know that it's there.
http://www.realclimate.org/index.php/archives/2016/11/record...
There was a lot of crowing about sunspots a couple years back by Judith Curry et al. The Earth's heating can be explained by reaching a solar maximum! Etc.
But now the situation is reversed--the sun is cooling--and despite that we're on track for yet another record year of heating. Third in a row.
Her points about model uncertainty and overfitting have some limited level of validity. But it's hard to read her blog and not come away with the accurate takeaway of she'll say whatever she can to provide a cover story for not doing anything about AGW.
