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Frank

LRC: The weather during the melt saison is for sure a factor for the amount of melting ice. Anyway, it's the elefant in the room? According to this: https://usclivar.org/sites/default/files/meetings/2014/amoc-abstract/ZhangR_AMOC2014.pdf the AMOC has a big influence on melting. And it's in decline... The "0" in the linked diagram is 18.000 km³, this was the amount of lost seaice in 2010 and 2012 which were (negative) outliner during 1979...2014 for march-september. My tip: september volume 2015 between 4.9 tkm³ ( melting just like 2010) and a bit more than 8.4 t km³ ( melting like 2014).

Artful Dodger

Lord Soth wrote | April 01, 2015 at 02:14

"The big question is, will that shrinking donut hole of ice free central arctic completely freeze over. If not, expect a regime change to a ice free central arctic during the winter."

Indeed, L.S. In fact the only way Climate Modelers have been able to reproduce mid-Pliocene (3.264 to 3.025 million years ago) temperature in the Arctic is by forcing Winter sea-ice extent to zero:

Ice-free Arctic winters could explain amplified warming during Pliocene

During the mid-Pliocene Warm Period (mPWP), global temperatures were just 2-3°C warmer than today, yet annual Arctic temperatures were 10-20°C warmer than today. This is important because during the mPWP, atmospheric CO2 concentration was also around 400 ppm. With a similar configuration of continents and mountain ranges compared to modern times, the mPWP is considered an important analogue for the 21st Century climate.

Cheers,
Lodger

Artful Dodger

Currently, a lot of work is underway comparing the paleoclimate record to Global Climate models in order to determine why those models vastly underestimate Arctic warming during the mPWP (about 3 million years ago). Here is one such study:

Howell, Fergus W., et al. "Can uncertainties in sea ice albedo reconcile patterns of data‐model discord for the Pliocene and 20th/21st centuries?" Geophysical Research Letters 41.6 (2014): 2011-2018.

A comprehensive review paper is in Prepress for Nature Communications which outlines progress, challenges and future direction in efforts to integrate pliocene geological archives and climate models.

I'll alert the group when this paper is published online by Nature, or if you can't wait msg me on the ASI Forum for a pointer to the draft copy.

Cheers,
Lodger

navegante

A. D. You really think that period is comparable? Regardless CO2 the atmospheric gas composition should be extremely different. And the geo-dynamics too. These independent of albedo

C'mon!

navegante

Note: I don't deny scientists find elements in common, but as you said, they have to force the winter ice free, meaning they dont know how to explain climate characteristics within model without ad hoc forcing. So much for providing understanding on current climate.

Philip Cohen

Incredibly arrogant navegante:
What reason do you have to claim that the atmospheric composition should be 'extremely different'? Or the geodynamics?
Why do you think that you are so brilliant that you have thought of something that all the professional climatologists never thought of investigating?
Does it make you feel better to know that, insofar as climate models don't match the Pliocene, it's because they underestimate the dangers of global warming?
C'mon!

navegante

Incredibly agressive Philip,

Yes, you are right I didn't express myself correctly. I seemed to be dismissive of the work of climatologists, which I only superficially know. That and the c'mon thing.

I will try to explain myself. A.D. says climate modellers need to add forcing winter ice free in order to reproduce the mid-Pliocene climate.

Climate modelers reproduce AGW: their models start by reproducing past years climate evolution under increasing CO2 levels, and continue with predictions of the near future warming climate. If they underestimate or overestimate warming, nobody really knows. Did you see how uncertain the 2100 global temperature projections are?

Now, do we really need to force an ice-free winter in the models to obtain the response we want? Don't you think it is more satisfying that a model predicts ice-free winter rather than requiring that condition for whatever?

But models do not predict ice-free winters in this century. Not that I have heard of.


Tor Bejnar

Lodger,
I'm not certain when the Isthmus of Panama closed. Some say earliest Pliocene; some say mid-Pliocene (3.1 ma - in the middle of your 'forced ice-free Arctic period' (http://geology.geoscienceworld.org/content/6/10/630.abstract). The timing of its closure, and the consequent changed ocean circulation, may have a significant influence on Arctic sea ice. Modeling global currents with an opening between N. and S. America must be tough.

navegante

Philip,
Sorry. You are again right about the atmosphere composition not being essentially different. I got confused on that.

Philip Cohen

navegante,

I responded, let us say, forcefully, because your original notes struck me as typical denialist crap. But no self-respecting denialist would ever admit to being wrong.

However, though you might be not be a denialist, you are still missing the point of the posts you replied to: climatologists do not force their models in order to account for Arctic paleowarming. They use the fact that they can't reproduce it without forcing as an impetus to improve their models so that natural inputs give accurate outputs. Which is what you want. And A.D.'s paper is an attempt to use information from the mismatch to improve.

And this is no excuse for denigrating current models. 'All models are false, but some models are useful.' With all their uncertainties, models are the only predictive climatesensitivitometers we have, and they have far better records than the denialists'. When planning for the future, we have to use the best methods we have now, not the best we'll have in ten years.

Al Rodger

Tor Bejnar,
Timing-wise, the appearance of the Panama Isthmus in terms of shutting off ocean currents can be different to the isolation of Pacific from Atlantic eco-systems.
In terms of climate, Drakes Passage between Antarctica & S. America wasn't simply open or shut. And it too may have played a part in mid-ploicene climate change. It had been open for some millions of years but was still widening in the mid-pliocene, having suffered a bit of a squeeze in the early Miocene (c25-15my), according to Lagabrielle et al (2009). For ocean currents, it seems size matters.

Tor Bejnar

Al,
Thanks for the Drakes Passage info (another challenge to Pliocene ocean current modeling). I have no doubt that 'size matters' and I also wonder what effect 'some connection' has.

Al Rodger

Tor Bejnar,
You whetted my appetite so I went looking. I soon was finding talk (eg "How the Isthmus of Panama Put Ice in the Arctic" by Haug & Keigwin) that the Panama gap had closed as a significant feature on the climate by 4.2 million years ago but it required something else to kick the Arctic into proper icy conditions a million years later.
The orbital obliquity which is one of the theories mentioned as a trigger(or the lack of orbital obliquity stopping the trigger 4.6-3.1My) is plotted in this earlier Haug & Tiedemann & paper.

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