A bit about climate change
Save This Post as PDFRecently, an idea that sharp terrestrial climate change might be directly correlated to spiral arm passages of the Solar system became very popular. Namely, certain correlations of times of spiral arm passage with timing of ice ages and abundance of 
in fossils were claimed to be found (in the latter case, effective abundance of grows if gets locked up in ice). The basic idea is that if Solar system goes through spiral arms of the Milky Way, the event rate of cosmic rays in the Earth’s atmosphere greatly increases (since the number of supernovae in spiral arms is clearly much larger than in between the arms) and this presumably affects formation of clouds and therefore strength of greenhouse effect. However, in reality we don’t know very well when Solar system passed between the Galactic arms to make sufficiently strong statements about presence of such correlation.
In their recent paper “Testing the link between terrestrial climate change and Galactic spiral structure” Adrian Melott with collaborator debunk this hypothesis using new data about structure of the Milky Way (Englmaier et al., 2008 – see Fig. below from their paper).
Current location of the Solar system is shown by black dot; units on axis are kPcs.
The result of the study is that any such correlation as well as any periodic trend related to the rotation of the Galaxy is absent.
Via sergepolar.
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Well, the only problem with their calculation is that it contradicts experiments. The existence of the 140-million climate period may be seen in 4 different and independent ways, see the picture
http://lh6.ggpht.com/_4ruQ7t4z.....rcFig6.jpg
(reopen the URL by alt/d copy/paste enter) which is a part of
http://motls.blogspot.com/2004.....ature.html
Their paper doesn’t really address either of these things, so one may pretty much say that they ignore all of observations and experiments on the subject.
Their statement that the periodic patterns don’t appear for any pattern speed is pretty much equivalent to saying that the Milky Way is not a spiral galaxy.
What really matters for these correlations are 3-4 recent cycles, see the sine waves
http://lh5.ggpht.com/_4ruQ7t4z.....e-ages.jpg
and sorry, their caricature of the galaxy is not enough to demonstrate that there are no 3-4 almost equally spaced waves in the structure of the Milky Way. For a different recent reconstruction of the arms that shows these waves rather clearly, see e.g.
http://en.wikipedia.org/wiki/F.....y_Arms.svg
http://en.wikipedia.org/wiki/Milky_Way
Their paper seems to be pure rubbish. It seems that they have deliberately chosen a dataset that obscures that the Milky Way is a barred spiral galaxy, added additional noise to destroy any remaining traces of structure, in order to claim that there are no quasiperiodic events in the Galaxy, even though it must be damn clear to everyone who has already seen at least one galaxy that such phenomena surely exist.
Some more comments of mine about it:
http://motls.blogspot.com/2009.....slava.html
Dear Lubos,
I agree that their picture sucks
(Wikipedia’s one sucks a bit less but it still does), and of course it would be stupid to claim that the motion of spiral galaxy does not feature any periodicity. My impression is that they are saying somewhat different thing: periodicity in the motion of galaxy does not mean periodicity in climate change. The connecting link here is cosmic rays which presumably lead to formation of clouds – it seems that even Shaviv is not completely sure whether the link does exist: “If the Cosmic Ray Flux climate link is real…” (that’s from his website)
Cheers,
Dmitry.
Dear Dmitry, Nir Shaviv is a scientist (besides being a boss of a terrifying socialist construct at his university, a labor union haha), so he obviously thinks impartially and neutrally about all possibilities.
But the fact that he is doing so is not an argument weakening his correspondence. In fact, quite on the contrary. I know that it has become fashionable to parrot financially motivated people and believe them just for their being loud and obnoxious – but you must know that I consider the loud people moral trash and the people who trust them are naive gullible idiots.
The radiation-cloud link is more natural and probably more robust and influential than any other widely proclaimed climate driver, it just extends the cloud chamber phenomena to a different regime, and it is now being tested at CERN (CLOUD).
You are definitely wrong that they’re saying that our motion through the Galaxy is periodic. Quite on the contrary, their whole paper is about their desired statement that there is no periodicity. Just read it, or is one of us illiterate?
They have absolutely nothing to say about the very mechanism whether a periodic motion would cause a periodic climate change – because they only try to deny the first part, the periodic motion through the arms. Just read it and stop spreading fog just because it suits your socialist perversion that you share with these low-quality astronomers.
Dear Lubos,
Thanks, if I must, I’ll keep that in mind.
Well, if you read the paper as carefully as you claim you did, you’ll find that they do talk about periodicity – period of orbital motion of Solar system is about 500 MYrs. Also, you might want to take a closer look at Fig. 2, from which it is rather clear why they were unable to fit it with periodicity of ice ages.
So, I was right, it’s a fixation, isn’t it?
You know, I think, you did not have to call Mrs. Hossenfelder “socialist bitch” since it does demonstrate how different things are connected in your brain 
Cheers,
Dmitry.
Once again, they do talk about periodicity, claiming that the actual motion through the arms or density waves is not (quasi)periodic, as shown in the figure as well as the whole paper.
They have nothing to say about the question whether a different density of the galactic matter around influences the temperature on Earth.
I insist that if you can’t reproduce the observations about the paper above, you are either illiterate, or dishonest, and your socialist perversion is the only sensible way to explain why you jump on the first shitty paper and endorse it in an attempt to throw 1/2 of the geological climatology in the toilet.
They certainly didn’t achieve anything of the sort, and this time, not even the politically correct media had such a bad taste to join your celebration of this trash.
Incidentally, as I have explained previously, all their (uncited) figures for the periods are wrong. No 500+ million years here, see
http://en.wikipedia.org/wiki/Milky_way
For example, the bar pattern rotation period is between 15 and 18 million years, the Sun’s galactic rotation period is 220 million years, the spiral pattern rotation period is 50 million years, etc.
You have simply endorsed a paper that is a manifest crap, and I ask you: what’s your alternative explanation, different than mine, why you did it?
Dear Lubos,
actually, it was a repost of friend’s blog post – http://community.livejournal.c.....63221.html – I was lazy enough not to write anything original, authored by myself that day
Actually, I thought the paper is rather boring (so I do deny that I celebrate the paper 
) but then you made it fun. Anyway…
I guess, your criticisms should be really applied to the Englmaier et al. paper where they report the CO distribution they constructed (the one they later use for periodicity analysis in the newer paper). Why CO distribution should differ from H distribution – I have no idea, do you? Gravitational clumping should work similarly.
Their model does differ from the one you have wrote about – for example, they claim that Milky Way has 4 arms instead of two, as follows from GLIMPSE study, this would change the result, wouldn’t it? This is regarding inner structure of the Milky Way, as for the outer structure, they say that
so no surprise why they were unable to find 140 MYr periodicity. For example, on the Pic. 2 of the recent paper you can see that according to them Solar System crosses arms approx. two times more frequently than one would expect from 140 MYr periodicity.
I do find it surprising though that there are still debates whether Milky Way has 4 arms or 2 (or superposition m=2 and 3).
Cheers,
Dmitry.
Dear Dmitry,
isn’t it enough to compare the two pictures of the galaxy, the conventional and the reconstructed “CO” caricature, to see that they’re different? Why are you trying to argue that they’re identical if they’re manifestly different?
By the way, there exists a very good reason why the distributions might be different for different compounds. H and He measure the normal matter from nucleogenesis, while heavier elements already depend on fusion in pre-existing stars. Your comment about gravitational clumping is based on the incorrect assumption that when the galaxies were being formed, there was carbon monoxide flying in the “air”, meaning the un-clumped intergalactic space without structures, waiting to be clustered with others.
There are many questions that are too loosely connected. Needless to say, the GLIMPSE study is way more reliable a source of information about the number of arms than their previous carbon monoxide paper with 0 citations, although I wouldn’t make a 1000:1 bet.
(Discussions exist even about the validity of string theory vs loop quantum gravity, as of 2009, or evolution vs creationism, or quantum mechanics vs hidden variables, so I am not shocked that people debate the shape of a galaxy whose neat map we can’t observe.)
But I don’t really believe that the quasiperiodicity of the density of rays around us is a fact that depends on the number of arms too much. They want to paint too many previous insights as coincidences and their arguments are just not strong enough for them. With 2 or 4 arms, there will be quasiperiodicities.
If you think that the observed 140-million-year cycles on Earth have nothing to do with the galaxy, where do you think that such a superslow process comes from? Or do you feel that this question doesn’t have to be answered by a theory whose very purpose is to replace the previous answers on the very same question?
Cheers
LM