12 April 2009

Semi-open thread 1

This is the first semi-open thread for the blog, as opposed to the many question place threads. Please first read on commenting before putting up your comment. Given other comments I've been receiving lately, I'll also suggest reading:

Cherry Picking
Why you need 20-30 years to decide climate trends

Questions are, of course, welcome here as well!


Bayesian Bouffant, FCD said...

At least five pirates have been killed in the last few days. Do you expect this to have an appreciable effect on global warming?

jg said...

Mr. Grumbine,
Thank you for your semi-open thread. I'd like to appeal to your astrophysics background and get you talking about astronomical forcing (Milankovitch cycles) using your stated goal of high-school level language. Let me share what I'm doing. It's been 25 years since I touched any high level math, so I'm trying to get tutorial-style information that will help me with a project that I've started here: http://www.brightstarstemeculavalley.org/pages/Astronomy.html

From this page you can select the EarthOrbitClimate link to see an interactive illustration on orbital forcing. I used this illustration as the basis for a presentation on orbital forcing to my astronomy club. The reaction from my club reinforced my belief that this topic is a great way to broach the subject of climate change in groups that are otherwise hostile to the subject.

I've asked questions on this subject on a few climate blogs, and one recently replied that he would like to see a good tutorial on the subject:

Thank you,

John G

Robert Grumbine said...

jg: Very nice displays at your page. One typo -- current obliquity is about 23.5 degrees, not the 22.5 on your page. The most recent citation for figures on this through geologic time I know is probably Laskar, J. et al, Astronomy and Astrophysics, 428, 261-285, 2004. Older, and crucial to much of our establishment of Milankovitch cycles as driving long time climate change is A. Berger, J. Atmospheric Science, 35, 2362-2367, 1978.

The prime source for this and other questions you were asking over at initforthegold would be Canon of Insolation and the Ice-Age Problem, Milutin Milankovitch, 1941. If was reissued in 1998 by Zavod Za Udzbenike I Nastavna Sredstva, Beograd. This version included a biography of Milankovitch.

Since my first paper was on ice ages and Milankovitch cycles, one of these years I'll be doing some introductions to how it works, and how we know that it does. In the mean time, you might be able to get Ice Ages: Solving the Mystery by John and Katherine Palmer Imbrie. It's an old book (about 30 years now), but it is by one of the people most involved in the work (Hays, Imbrie, and Shackleton, Science, 1976).

jg said...

Thank you, for the references and for catching my error. I've corrected it, and that should improve my credibility by a degree.

I look forward to your in depth treatment of this subject.


Anonymous said...

I read your FAQ on sea level rise, a very informative article. It raised some questions though. I’ve read that the higher sea levels during the Emian period 125000 years ago (~5 meters higher on average than today, whereas the temperature was only 1-2 degrees higher ) were partly due to Greenland and partly to the West Antarctic Ice Sheet (WAIS). If that’s true, than the Greenland ice sheet is absolutely relevant for sea level rise (SLR). The issue may be –as you state- the rate of change: Perhaps the first few metres of SLR during the Emian were dominated by the WAIS and the last few metres by Greenland?

A related issue is how significant the difference in estimated speed of melting is for those two ice sheets: “A few centuries” doesn’t sound very different than “several centuries”.


Robert Grumbine said...

Bart: The inconsistent language is one of the things I want to clean up in that old (vintage 1997) faq. Also, in the time since the FAQ, we've discovered that Greenland is a lot less stable than we'd thought.

Given my current understanding of both Greenland and WAIS, I think the line to take is that probably the 121,000 years ago (121 kya) sea level rise was a mix of both Greenland and West Antarctic. Probably about even between the two.

Anonymous said...

I saw a few comments here on how high CO2 atmospheric concentrations could get with economically recoverable oil, gas and coal reserves (with no meaningful emissions restrictions) . I found a couple of links




(linked from the first article)

How far beyond 2* pre industrial CO2 can we really go ? (Incidentally, I can see 2* pre industrial CO2 is likely to have some pretty severe effects & may have some disasterous ones)



Hank Roberts said...

This might be worth a look and explication (I only have access to the abstract), re trend detection:


"... A sensitivity test of the climate trend detection demonstrates that the method developed in this study can accurately detect an arbitrary climate trend which is introduced into the time series."