2011-06-24 05:19:51Milankovitch Cycles, Orbital Forcing
jg
John Garrett
garrjohn@gmail...
108.23.2.2

I've been drawing some illustrations for Steve Brown's Eemian series, and this has emboldened me to ask if I could create a post or collaborate with someone on the Milankovitch theory. You may have this topic covered, but I haven't found the post, and a search of this forum revealed that you've avoided mention of Milankovitch theory (too technical or off target for your audience). I did find John C's recent question about a Nature article that poses a challenge to Milankovitch theory. So maybe there's some intererest.

In the illustrations I'm doing for Steve, it occurs to me that some background information, eg. how precession is calculated, could be provided in another post so that Steve's article doesn't have to get too deep in the astronomy angle. Planning for such a post may also help streamline what Steve discusses regarding orbit.

This project also falls in with a personal goal. I'm revamping my Earth, Orbit and Climate presentation for a astronomy event in August. One of the event organizers broadcast a comment that solar predictions portend another little ice age. This comment got a couple "likes", so I want to be there with my best presentation, and the illustrations I plan to create could be used here and there.

thanks,

John Garrett (jg)

2011-06-24 05:37:20
Steve Brown

brownsg@gmail...
80.177.115.133

Go for it John.  I was wondering myself if there was already a post on it that I could link to from my series.  If you are able to do it in the near future then I can link to it for my part 2 post.

One request - can you please mention James Croll?  He was the Scottish scientist who actually devised the connection between orbital configuration and climate and used it to explain the glacial/interglacial cycle discovered by Louis Agassiz.  Unfortunately, Croll struggled to get acceptance for his ideas.  It was Milankovitch that picked up Croll's baton and perservered with getting the theory accepted several decades later.  It's a real shame that Milankovitch stole the limelight.  The fact that I'm Scottish has no bearing on this whatsoever...honest.

2011-06-24 07:24:23
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.112.151

JG - yup, we've talked about covering that subject properly, but that's about as far as it got. The graphics you've produced look great. Go for it!   

2011-06-24 11:15:40
Chris Colose

colose@wisc...
69.86.130.70

I'd be happy to help in some of the theoretical aspects of Milankovitch cycles, both on Earth and other planets.

2011-06-24 14:04:54
jg
John Garrett
garrjohn@gmail...
96.229.221.76

Thanks all, for your encouragement.

Chris, I've been an admirer of your writings here, at RealClimate, and at your blog. I eagerly accept your help.

I want to finish a couple illustrations for Steve, after that, I'll start posting some illustrations and an outline. I have an idea of where to start, and I welcome any suggestions.

jg

2011-06-25 01:48:35
Steve Brown

brownsg@gmail...
91.220.25.25

I think Chris's idea of expanding it to other planets too would be very worthwhile.  It would be a good rebuttal to the "Mars is warming" type arguments if you can clearly show how other planets will receive varying insolation over successive orbits.

2011-06-25 04:02:33Mars and orbital forcing
jg
John Garrett
garrjohn@gmail...
108.23.2.2

I agree with including other planets, though if I'm not mistaken, Mars is the only one in mind. Laskar, whose data I've used liberally, has also calculated orbits of Mars, and he is connected to some papers discussing Croll/Milankovitch orbital forcing in Martian icecap deposits. There's a lot of potential here.

2011-06-25 15:52:26
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.16.30

JG, what would be cool is side-by-side images of the face the Earth presents to the sun; between the maximum and minimum stages of obliquity. Would complement that graphic of the astronomical cycles you've produced for Steve, and be a handy pointer for blog commenters in the future.   

2011-06-26 01:55:46
jg
John Garrett
garrjohn@gmail...
96.229.221.76

Rob, Good suggestion. I'll work on it.

jg

2011-06-28 13:09:39Illustration of Earth's tilt extremes
jg
John Garrett
garrjohn@gmail...
96.229.221.76

Rob, is this about what you envisioned?

Earth's Tilt

2011-06-28 18:38:24
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.115.234

JG, I was more thinking along the lines of a shot of the Earth leaning toward the viewer, perhaps Asia/Europe/Africa (the main bulk of the land mass) at minimum obliquity and then maximum.

Excellent stuff by the way, a picture being worth a thousands words and all that. 

2011-06-29 00:16:47Illustration: Changes in tilt vis-a-vis major land masses
jg
John Garrett
garrjohn@gmail...
108.23.2.2

Like this?

Earth's Tilt vis-a-vis the major land masses

 

And for good measure, here's one showing the Americas and Australia:

Earth's tilt looking at America and Australia

2011-06-29 21:42:32
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.106.249

Sweeeeeet! The green line for comparison between the two is a great idea.

2011-07-01 05:42:39Illustration: Eccentricity and apparent size of the sun
jg
John Garrett
garrjohn@gmail...
108.23.2.2

This illustration and others like it that I'm working on may do well in a basic Milankovitch cylces post. I took the sun photos, so there's not copyright issue.

jg

 

Earth's Orbit: Eccentricity and apparent size of the sun

2011-07-01 06:30:25
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.6.156

A basic version of Milankovitch would be great JG, it's one thing that many bloggers are genuinely confused about.

2011-07-01 23:51:44
jg
John Garrett
garrjohn@gmail...
108.23.2.2

Another illustration I'd use in a basic orbit/milankovitch post. This shows that precession has real implications and will lead into an explanation of the difference between astronomical precession and climatic precession (a distinction often lost among astronomers):

Precession visible over 50 years on a star map

2011-07-02 00:41:47Perhaps...
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

The last chart reminded me of an astrological chart. Perhaps SkS should start a Astrology series? (Sorry, it's been a long week.) 

2011-07-02 00:46:27
jg
John Garrett
garrjohn@gmail...
108.23.2.2

Actually, astrology recently corrected itself for precession though this made no change to its predictive skill.

But mentioning it could have an interesting angle.

 

2011-07-06 12:03:28
jg
John Garrett
garrjohn@gmail...
96.229.221.76

I tried my hand at a basic level post on this topic:

Orbital Forcing

My post walks the reader through a series of illustrations, an approach that may not be desirable for SKS, or my aim may be too basic for the target audience. Blunt, honest feedback is welcome.

If can turn this into a usable post, I hope it will serve to keep Chris Colose's recent draft on the same topic focused at a hire level reader.

There are also a few details I need advice on, but before I ask, I'd like to see what others think of what I have so far.

thanks,

j

2011-07-06 13:12:38
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.250.27

jg- some suggestions:

1. Too many graphics for one post. Too much to digest for the layperson. Maybe break it in two?

2. Context. You need a hook to make it relevant to global warming. A discussion about Milankovitch without relating it to what we discuss here makes it a dry read. "Climate's changed before" is a common logical fallacy used by "skeptics", maybe that's your  'angle'?

3 Awesome graphics!

 

2011-07-07 00:12:59
jg
John Garrett
garrjohn@gmail...
108.23.2.2

Thanks Rob. Very helpful.

2011-07-07 01:04:53
Chris Colose

colose@wisc...
128.183.2.130

I will try to modify my own Milankovitch post today or tomorrow.  Sorry, been very busy in the last week.

2011-07-07 20:19:47
Steve Brown

brownsg@gmail...
91.220.25.25

An excellent start.  As Rob says, it would be an improvement to split it into 2 posts.  It also needs an introduction to put it in context, such as it being the main driver of glacial / interglacial cycles and it was the puzzle of these regular cycles that got Croll and Milankovitch interested.  You could maybe finish of with including a simplifed version of: http://www.skepticalscience.com/pics/orbitParams_wUnits_lg.jpg and a mention that we can see the influence of the orbital components within sedimentary rock strata, ice and sediment cores etc.