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Author Topic: Tony Brown writing at judithcurry.com  (Read 4362 times)

anonymous

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Tony Brown writing at judithcurry.com
« on: April 14, 2013, 12:16:12 AM »
Has anybody made it through this possibly longest arctic sea ice history blog post ever? There is a rumor sea ice controls OHC to be published as a paper? soon. Anything else I've overscrolled?

Neven

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Re: Tony Brown writing at judithcurry.com
« Reply #1 on: April 14, 2013, 12:48:10 AM »
I'm not sure it's the longest Arctic sea ice history blog post ever, as I believe Tony Brown has published similar blog posts for WUWT and Jeff Id's blog.

I actually read 90% of it, it's quite interesting. I discussed a bit with Brown as well. As I believe he concluded, melting season minimums in the period between 1920 and 1945 were far from matching 2007, 2011 and 2012. Which is why personally I won't invest my time into sorting out the details, but it'd be great if someone would take all that anecdotal evidence and quantify it by producing a map and some approximate numbers. Although I wouldn't be surprised if several scientists have already done as much, even though Brown maintains that ice area during that period is massively overstated.

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TerryM

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Re: Tony Brown writing at judithcurry.com
« Reply #2 on: April 14, 2013, 04:45:12 PM »
Doesn't the presence of the Ellesmere ice shelves throughout the period preclude melting comparable to post 1979 melts?


I didn't read the whole thing, but did search for "Ellesmere" "Ward Hunt" and a few other words/phrases within the tome. I don't understand how one could compare the melt we've been witnessing to prior melts without such references.


Terry

ChrisReynolds

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Re: Tony Brown writing at judithcurry.com
« Reply #3 on: April 14, 2013, 06:30:34 PM »
Interesting post, really it just reinforces how sensitive the Arctic region is to perturbation. It doesn't surprise me that the changes were likely to be more widespread than some of the literature indicates.

Someone in the comments there makes reference to ice 'peaks' as deep as 100ft (A fan of *MORE* discourse  |  April 10, 2013 at 10:30 am). This would be about 30m. Given the resolution of PIOMAS and the appearance of grid boxes of the order of 7m effective thickness in earlier years, this does not preclude thicknesses of 30m at the upper end of the distribution. Contrary to what that poster suggests I think ridging could probably rebuild thick ice within a decade or two, provided forcing was not inimical to ice as at present.

Terry M,

Vincent shows that the collapse of Canada's ice shelves has been a long term process throughout the last century, not just restricted to the recent warming.
http://www.cen.ulaval.ca/warwickvincent/PDFfiles/149.pdf

Neven

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Re: Tony Brown writing at judithcurry.com
« Reply #4 on: April 14, 2013, 07:50:55 PM »
However, La Curry herself said two years ago:

Quote
IMO, the strongest argument for sea ice decline over the last decade for being unusual and at least in part attributable to global warming is this (from Polyakov et al.): The severity of present ice loss can be highlighted by the breakup of ice shelves at the northern coast of Ellesmere Island, which have been stable until recently for at least several thousand years based on geological data.
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ChrisReynolds

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Re: Tony Brown writing at judithcurry.com
« Reply #5 on: May 17, 2013, 07:11:24 PM »
I had found the argument put forward by Curry persuasive (although I read it elsewhere). But when I read into the subject more, and came across the paper I linked to, I was less certain.

On balance I do think that AGW's forcing has been going on for much longer than the last few decades. As persistent ice integrates impacts upon it (it's persistence from year to year means it holds a 'memory' of all impacts upon it), it is much more sensitive than seasonal ice or ice that is replenished. Here I mean ice that either grows during a cold period, or ice in outlet glaciers.

The ice sheets, having been persistent ice, therefore were probably more sensitive to small early years anthropogenic forcing.

However this isn't as strong an argument as implying the ice shelf loss happened in the last several decades, which by my reading is factually incorrect. Massive loss of shelf area seems to have been happening during the first half of the Twentieth century.

PS - see figure 3 of the paper I linked to in my previous comment.

Peter Ellis

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Re: Tony Brown writing at judithcurry.com
« Reply #6 on: May 17, 2013, 11:13:39 PM »
As persistent ice integrates impacts upon it (it's persistence from year to year means it holds a 'memory' of all impacts upon it), it is much more sensitive than seasonal ice or ice that is replenished.
Can you expand on this?  It seems absolutely backwards.  Seasonal ice will respond rapidly because it only cares about the current conditions (warmer than previous).  Persistent ice will respond much more slowly because it still holds onto the memories of past, colder years. It's like saying a lake will evaporate before the puddles around it.

ChrisReynolds

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Re: Tony Brown writing at judithcurry.com
« Reply #7 on: May 18, 2013, 08:17:27 AM »
Seasonal ice regrows thermodynamically, the ice in outlet glaciers ice replaced with new ice from the mass of (Greenland in this case) ice behind it. So any impact on this due to a succession of warm years can rapidly disappear when there's a succession of warmer years, as this sort of ice is being regularly replenished.

However thick MYI, or landfast ice shelves, would be impacted by any warm period. And because this ice is more persistent when a cool period comes along the effect of the warm period would remain. So that when another patch of warm years arrives the ice still carries the 'memory' of the previous warm period into the new warm period.

Essentially it's due to time constants of the ice. In terms of sea ice FYI has a short time constant, MYI has a long time constant. See Bitz & Roe, "A Mechanism for the High Rate of Sea Ice Thinning in the Arctic Ocean." Journal of Climate"
http://www.atmos.washington.edu/~bitz/Bitz_and_Roe_2004.pdf

However as the basics of this is thermodynamic growth of ice, it seems that the argument can be expanded to landfast ice shelves, and by virtue of replenishment in outlet glaciers an analogous argument can be made there.