 one of them with their own view, which disagrees. If you only looked at the RealClimate page, you might not be aware that it only partially addressed a couple of the points made. If you only looked at Shaviv’s page, you might be unaware that there were any arguments against. (Although that seems unlikely!) By reading both, you would learn that meteorite analysis apparently showed a history of variations in cosmic radiation, but that these might not be the result of passing through the galactic arms as Shaviv indicated.
Plus of course it’s just as possible for RealClimate to be wrong, too. It isn’t safe to take the existence of a rebuttal on RealClimate as the final word on the subject, either.
If you want to know which bits are controversial and which not, you have to read more widely than a single source, and you have to actively engage your critical faculties, even (some would say especially!) on subjects thought to be well established.
I would certainly agree that it is helpful to have read some basic meteorology or atmospheric physics texts first to be familiar with the concepts and terminology. But that is not a quick study.
As Tom Wigley once said with regard to climate science: “No scientist who wishes to maintain respect in the community should ever endorse any statement unless they have examined the issue fully themselves.”
Wise advice, I’d say.
Nice reply, Nullius!
I hope you and David Corfield talk a lot here on this blog, because you seem a bit less eager to “shoot down” his questions than some here, and perhaps a bit more interested in actually engaging with them — and that would be interesting, because David, as far as I can tell, is actually interested in talking about ideas, rather than pushing an agenda.
N.i.V.,
I guess I know pretty well what is science and what is rhetorics. I know referring to creationism sounds a bit rhetoric… First I tried giving an example from mathematics: Learning number theory from studying pre-Wiles Fermatism. (But then, maths is perhaps a bit different business. Still, the working mathematician has to take the word of others when it comes to large theorems. E.g. many use Atiyah-Singer index stuff without having checked every detail of proof(s) before – those will one day sink in by osmosis. Likewise, I trust the Poincare conjecture is true, the four color theorem is true, etc. – even while I never ever will check the proofs.)
OK, so back to Shaviv. (Note that I haven’t bothered giving this more than half an hour of thought, for I think it’s a waste of time. My arguments should be checked independently.) Shaviv is actually an excellent example of how to proceed for the amateur climatologist:
1) The greenhouse effect is undisputable. But Shaviv states here,
2) Climate models can reasonably reconstruct historic temperature (cf. e.g. the figure in Kerry Emanuel’s essay) – even while clouds are a major factor of uncertainty (cf. op. cit.). So, it is highly improbable that cosmic rays (impacting cloud nucleation) are a significant climate forcing. Anyhow, the cited RealClimate article states,
3) The Sun’s influence on climate is well-known by mainstream climatology, so it is not to be expected Shaviv has anything significant and substantiable to add (otherwise it would have been accepted by mainstream wisdom).
Conclusion: Studying Shaviv in detail would be quite a distraction from learning the real stuff. You can safely disregard him – except you actually don’t want to learn about climatology.
(P.S.: And yes, I know this is heuristics. But pragmatico-necessarily so. I will now take my conclusion seriously and say no more.)
I’d like to know the range of proposed mechanisms for solar climatic influence. Is the decreased solar activity-more galactic cosmic rays-more low altitude clouds mechanism the best supported? The CLOUD experiment must presumably have been well regarded for CERN to have accepted it. Jasper Kirkby gives a lecture on the experiment.
I’m a little less impressed by NiV’s reply, John, probably because I’ve seen variations on that theme so many times. It doesn’t seem to me to have much content.
In any case I agree that examination of some actual ideas would be a good thing. Maybe a thread on Shaviv, if David agrees with NiV that it’s defensible material, or if not something else he can point to?
Thank you, Florifulgator. There’s a lot more that could be said, but what you said is sufficient. I hadn’t spotted the “any warming” passage on my quick read-through; that’s pretty funny.
Re the influences, David, it sounds as if you’ve already looked into this. If you’d like to discuss them, probably you should lay them out for others to comment on.
Re the CLOUD experiment, it’s a reasonable effort to get a handle on a plausible minor effect. Proposals that it’s a significant effect fail trivially on paleoclimate grounds. I’m sure you’ve seen that material as well. Why are you so interested in such a thoroughly rejected set of ideas?
Florifulgurator,
I quite agree that as a practical matter, a scientist must take a lot on trust. But such trust, while fully justified on a practical level, is not itself scientific. If challenged, it needs to be checked. And anything should be open to a plausible challenge.
The four colour theorem is a case in point. Kempe proved it in 1879, and I’m sure that for a lot of mathematicians that was good enough. But in 1890 Heawood challenged it, and mathematicians on hearing of it would have checked, and then reset it back to ‘conjecture’. Note, Heawood didn’t prove the four-colour theorem wrong, he only challenged whether we had the evidence to prove it.
On Shaviv, I’m not sure if this is the appropriate place to be arguing this. If John wants us to stop, I’m happy to do so.
On point 1, I agree that the greenhouse effect is indisputable, but I also agree (subject to definitions and caveats) with Shaviv’s statement. They are talking about two different things.
I am in no doubt that there is a greenhouse effect, and that increasing CO2 will tend to increase temperature. But we cannot deduce from that that an observed increase in temperature is therefore due to CO2. There are *lots* of things that can change temperature, including I am sure many that are as yet unknown. The whole process is non-linear with many feedbacks and time delays, so you can’t even say it has made a particular additive contribution.
I have seen Shaviv elsewhere say that the solar correlation only explains about half of the observed modern change (IIRC), and I’d be confident that he’d agree that CO2 probably caused a part of the remainder.
On 2, climate models can reconstruct the global average, but they’re not so accurate on the details. The variances are wrong, the response to volcanic eruptions too large, and they come up with a different answer for the upper tropical troposphere trends – although the enormous uncertainties in the observations mean the significance of the difference is borderline.
The problem with models that have adjustable parameters is that they are capable of ‘curve-fitting’. Take any set of linearly independent functions (with generally similar smoothness characteristics to your target) as a basis, and you can approximate an arbitrary function with a weighted sum of them. Climate models are more complicated than that, of course, but the same principle applies. John von Neumann said “With four parameters I can fit an elephant, and with five I can make him wiggle his trunk.”
The global mean temperature anomaly is a one-dimensional summary for the entire planetary climate system. Fitting that is no challenge. Several sceptics have done so with linear combinations of PDO, AMO, and ENSO. I agree that climate models do a better job over a wider range of variables, but it’s not a perfect job, and I consider there to be a significant risk that the fit is partially due to a more subtle curve-fitting.
I take your point that they did make a reference to the cosmic ray data. I’m not going to chase the reference right now, but I’ll bear it in mind.
On point 3, I have seen mainstream climatologists discuss variations in the *thermal* contribution of the sun to climate, but that does not address the possibility of non-thermal influences.
The argument that if there was anything to it the mainstream wisdom would already have accepted it, I’ll put down as one of your ‘heuristics’. :-) I ‘ll say no more about it.
Commenting on the cosmic ray hypothesis generally, my view is that it is only another competing hypothesis, with even less confirmation so far than the AGW hypothesis. It’s based mainly on correlations (which do not imply causation) and some plausible but as yet unconfirmed possible mechanisms, and little in the way of experimental back up. But I think that’s mainly because it’s very new, and not a lot of people are working on it.
But I do think that as a hypothesis it is very much still in play, and that as people challenge it, it will continue to improve.
Challenging it on a technical level is healthy, and I’