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sidd

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Paleo modelling
« on: April 03, 2019, 11:37:11 PM »
Willeit et al. have a nice paper out on modelling the quaternary. They use CLIMBER-2 and SICOPOLIS for the ice. They even get the Mid Pleistocene transition (41KYr to 100Kyr periodicity for glacial cycle) right. And they get remarkable agreement with other paleo data.

Two things leap out at me:

1)the key role of regolith
2)they can do all this with a static Antarctic ice sheet.

Realclimate has a writeup, i have asked about 2) there. What would happen if you made WAIS dynamic, for example ?

They find that T never rose above 2C over preindustrial over the last 3 odd million years, and present day CO2 levels exceed any in the Quaternary.

Very nice. Open access. Read all about it.

http://advances.sciencemag.org/content/5/4/eaav7337

sidd
« Last Edit: April 04, 2019, 08:08:41 AM by sidd »

Bruce Steele

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Re: Paleo modelling
« Reply #1 on: April 04, 2019, 06:03:53 PM »
Sidd, Models seem to reinforce my bias towards carbon cycle influences of the oceans dominating terrestrial carbon influences.
"There, we demonstrated that glacial lowering of atmospheric CO2 in the model is controlled by lowered sea surface temperatures (SSTs) and changes in ocean circulation, in particular enhancement of Antarctic bottom waters and decrease of deep ocean ventilation. Elevated carbonate weathering on exposed shelves and enhanced nutrient utilization in the Southern Ocean due to enhanced dust deposition also play important roles, especially toward glacial maxima (27). Reorganizations of the Atlantic meridional overturning circulation during glacial terminations contribute substantially to deglacial CO2 rise. The terrestrial carbon cycle, which includes novel components such as permafrost carbon, peat, and carbon buried under ice sheets, plays a minor role in atmospheric CO2 dynamics on orbital time scales."

Thanks for the open access link

sidd

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Re: Paleo modelling
« Reply #2 on: April 07, 2019, 01:27:46 AM »
Some more detail on CLIMBER 2 ( the model used by Willeit et al.)

https://www.pik-potsdam.de/research/earth-system-analysis/models/climber/climber-2

The ice model is SICOPOLIS

http://sicopolis.net/

I am amazed that with a simple model like CLIMBER 2 they get the transition right. Especially with static antarctica. SICOPOLIS ice also leaves out some, their ice discharge/calving treatment is quite simplistic and "causes some problems"

https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/34755/1/Greve_2007_SICOPOLIS.pdf

Again i am amazed that they get so much right.

sidd


Pmt111500

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Re: Paleo modelling
« Reply #3 on: April 07, 2019, 06:57:47 AM »
Quick glance: the study emphasizes the role of Black Carbon and other minerals on glacial terminations, thus modifying the importance of various factors involved in glacier melt and build up.

Thanks for the link, I'm not actively trying to tackle this glacial conundrum of timings but some younger readers might want to read this carefully. Well, me as well if I can find the time to familiarize with this. Link to the quite detailed series of related matters, that maybe of help understanding the article, and the how the results may change former theories: https://scienceofdoom.com/roadmap/ghosts-of-climates-past/
Amateur observations of Sea Ice since 2003.

sidd

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Re: Paleo modelling
« Reply #4 on: April 07, 2019, 11:33:31 PM »
The Willeit result shows that

a) you dont need a dynamic antarctica for wither 40Kyr or 120Kyr glacial cycles
b) you dont need dynamic antarctica for the transition from 40Kyr to 120Kyr period

My amazement continues. I shall have to read the other PaleoMIP efforts carefully. In particular i would like to see an analysis for the Eemian to present, where we have more data.

sidd
 

El Cid

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Re: Paleo modelling
« Reply #5 on: April 08, 2019, 07:28:44 AM »
I became truly amazed by the poorness of the models when I read about modelling the Green Sahara. This one happened just a few thousand years ago and yet our models can NOT very well replicate it. Even with serious tweaking and vegetation feedbacks they only come close and not fully replicate the quite well established paleo record.
I think current models are not very good for forecasting changes in atmospheric circulation possibly because of poor understanding of cloud feedbacks...

Pmt111500

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Re: Paleo modelling
« Reply #6 on: April 08, 2019, 08:45:43 AM »
Some, a bit more detailed, thoughts.

"The CLIMBER-2 intermediate model includes a simplified atmosphere model which allows for runs of long periods.", or something like that.

The model used in this study is light compared to the full scale models that may lack some feedbacks. They're better suited for studies involving shorter periods ~ the 160-250 (maybe a thousand) year scale we have plenty of data to verify them against. And as they have been developed from meteorological models, they might use inordinate amount of resources calculating the atmosphere... Thus slow glacier feedbacks, such as have been postulated to be of influence f.e. in the Green Sahara periods, may not appear at all.

As we have seen marine glaciers may disintegrate very rapidly in Antarctica, it's prudent to test the various developing glacier models in these smaller climate models. The model used in this study should probably have a dynamic ice sheet model for Antarctica too, but they've opted to think the ANtarctic Circumpolar Current is a sufficient barrier. And the regolith-model used for northern glaciers doesn't apply in the southern pole, there are no such soils present under the evercold Antarctic icesheets.

Like *sidd*, I'd be interested on the more detailed results for Eemian-present. Could their glacier growth-decrese model send enough icebergs sailing shouth to produce the Green Sahara and glacial temperature variations observed from proxies?

They apparently get the large scale structure of atmosphere being correctly formed, with monsoons and other general fronts,  so maybe the model would show a persistent atmospheric river or an extra monsoonal effect over in dry Africa. The 10-16 levels mentioned in the model description is enough to resolve these then. Didn't quickly find the specs on the ocean model used, but it's of GFDL make and also used by them so it can't be extra bad. I don't know enough of the other modules so no comnent on them, let the results speak.

The high spatial resolution on the atmosphere in more complex models can be used in f.e. hurricane studies, EMICs (Earth model of intermediate complexity, if correctly remembered) do not find these (or at least didn't some 5? years back), and I'm of the opinion that ocean models should have (containing large amounts of latent heat) should have almost as many layers as the atmospheric modules, but this would likely mean lowering the amount of layers of atmosphere, to conserve disk space and computing time...

Ok, I think that's enough of a ramble on this. The study is such it presents imho a challenge to the teams working on the massive models. Had to read the realclimate write up first to get into the article, not finished with it yet, maybe in future.

« Last Edit: April 08, 2019, 11:22:59 AM by Pmt111500 »
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sidd

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Re: Paleo modelling
« Reply #7 on: April 08, 2019, 08:19:34 PM »
The ocean model is terribly simple also ... 3 basins, 1 layer ...

sidd

Pmt111500

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Re: Paleo modelling
« Reply #8 on: April 08, 2019, 10:22:44 PM »
I think they mean they don't do all the calculations in 3d
https://www.pik-potsdam.de/research/earth-system-analysis/models/climber and
https://www.gfdl.noaa.gov/mom-ocean-model/
Do not sound particularly weak.
« Last Edit: April 09, 2019, 08:13:46 AM by Pmt111500 »
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sidd

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Re: Paleo modelling
« Reply #9 on: April 08, 2019, 11:37:52 PM »
Farmer et al. have a paper out linking AMOC slowdown to MPT

doi: 10.1038/s41561-019-0334-6

i dont think the ocean model in Willeit has and AMOC, or does it ?

sidd

sidd

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Re: Paleo modelling
« Reply #10 on: April 09, 2019, 12:31:00 AM »

Pmt111500

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Re: Paleo modelling
« Reply #11 on: April 09, 2019, 06:18:09 AM »
CLIMBER 2 does have north atlantic meridonal overturning, fig 10 in

https://epic.awi.de/id/eprint/13572/1/Gan2001a.pdf

....
sidd

I just figured RealClimate wouldn't do a write up if this had been about a 20 year old dated model. Anyway the SICOPOLIS module, or a tweak to it, is the new thing here. VECODE I've seen used previously. Resolution isn't too great but hey, it works and gives out results we can verify and thus mostly believe in. (Spent about three weeks reading about a couple of models once in history, not starting again yet.)
 
« Last Edit: April 09, 2019, 06:24:44 AM by Pmt111500 »
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sidd

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Re: Paleo modelling
« Reply #12 on: April 09, 2019, 07:12:28 AM »
Climber 3 + dynamic antarctica in SIOPOLIS doing the Eemian to present would be fun ...

sidd

Pmt111500

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Re: Paleo modelling
« Reply #13 on: April 09, 2019, 07:39:45 AM »
Climber 3 + dynamic antarctica in SIOPOLIS doing the Eemian to present would be fun ...

sidd
As far as I can see, could be excellent, yes.
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El Cid

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Re: Paleo modelling
« Reply #14 on: April 09, 2019, 09:08:27 PM »
This is a great article comparing European Holocene Optimum data with models. In short: the models do not get it right as they don't really take into consideration possibble changes in atmospheric circulation.

Many great graphs and maps! Worth reading

https://www.stevenphipps.com/publications/mauri2014.pdf

My conclusion: further warming of the climate in the 21st century could bring very dry, sunny and warm summers for scandinavia (UK?) but cooler/steady summers in Southern Europe. Winters could get very much warmer than now in Northern Europe, and much drier in S.Europe.