Re: [Phys-l] Phys-l Digest, Vol 52, Issue 3

[kyle forinash <kforinas@ius.edu>]

Hi

The seasonal variation of insolation depends on orbital parameters and 
varies from around 450W/m^2 to 550W/m^2 at 65deg lat. 
(http://www.ncdc.noaa.gov/paleo/forcing.html). I think Brian is right, 
at the present time it is closer to 500W/m^2 than the 400W/m^2 I quoted 
earlier.

CO2 does lag climate change but it seems to be important for explaining 
the relatively rapid clime out of an ice age. Orbital variations are 
very gradual but the change from ice age to interglacial can be very 
abrupt (as short as ~10s of years- 'Abrupt Climate Change' R. B. Alley 
et. al. Science vol. 299 March (2003) p2005.). Ice cover also plays a 
feedback role. Without these feedbacks it is hard to explain how you can 
get a  shift in global average temperature of as much as 10C in as 
little as 100 years when the fastest orbital parameter change has a 
20,000 year period.

In regard to the Wilkin's ice shelf, it appears the breakup was 
predicted (I don't know whether from a model or trend or what) in the 
90s but predicted to take much longer (30 years):
(http://www.thaindian.com/newsportal/lifestyle/antarctic-ice-shelf-hanging-by-its-last-thread_10070400.html)

Climate models are tweaked as time goes on but the IPCC also has some 
interesting comparisons of past model predictions with current data:
http://physics.ius.edu/~kyle/ClassRefs/GlobalWarming_files/ts26.jpg

kyle
> ------------------------------
>
> Message: 10
> Date: Sat, 02 May 2009 09:08:10 -0500
> From: Brian Whatcott <betwys1@sbcglobal.net>
> Subject: Re: [Phys-l] global temperatures
> To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
> Message-ID: <49FC53CA.8010008@sbcglobal.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> kyle forinash wrote:
> > HI
> >
> > Some factoids (mostly from the IPCC). Although the total annual average
> > insolation remains constant for the earth over hundreds of thousands of
> > years (even including orbit changes- and changes in sun intensity occur
> > much slower), the LOCAL change at 60deg latitude is a seasonal variation
> > of around ~400W/m^2.
> Hmmmm...let's see: the overhead insolation  at the equator - let's call
> it 700 W/m^2
> So at 60degNorth, the insolation would be 700cos(60-23) = 569 W/m^2  in
> Summer,
> and  700cos(60+23) = 85W/m^2 in Winter.
> The LOCAL seasonal variation at 60 degN would be 569 - 85 = 484W/m^2
> The LOCAL diurnal variation is 569 W/m^2 in Summer, and 85W/m^2 in Winter.
>
> ....in other words, I don't get it - so I am missing something??
>
> Brian W
>
>
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>
> End of Phys-l Digest, Vol 52, Issue 3
> *************************************

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 "When applied to material things,
the term "sustainable growth" is an oxymoron."
	Albert Bartlett

 kyle forinash   812-941-2039
  kforinas@ius.edu
  http://Physics.ius.edu/
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