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Author Topic: Modulation of ice ages via dust-ice albedo  (Read 4488 times)

ralfellis

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Modulation of ice ages via dust-ice albedo
« on: December 31, 2015, 09:07:14 PM »
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I have written a paper on the mechanisms for ice age modulation that appears to explain all aspects of the glacial cycle. It is a novel idea that has not been previously mentioned to my knowledge.  The paper is being presented to a journal but I was looking for any feedback that may help improve it before publication.  The Introduction follows, which gives a good flavour of the arguments being made.

Thanks,
Ralph


Introduction.

Ever since their discovery almost two centuries ago, the dramatic ice ages and their likely connection to orbital cycles have captured the imagination and curiosity of scientists. A large amount of geological evidence has been assembled from a variety of sources, and many different hypotheses have been advanced to account for their approximate 100 kyr periodicity and asymmetric temperature response. The cooling phase into an ice age tends to be gradual and punctuated by transient reversals, while the interglacial warming is decisive and rapid, causing deglaciation within a few millennia.

The cyclical variation in northern hemisphere insolation caused by the combined effects of the precession of the equinox and the obliquity of the Earth's axis, was calculated by Milutin Milankovitch back in the early 19th century, while improved calculations have been provided more recently by Laskar et al. *0  The results of these endeavors clearly demonstrate that each major deglaciation coincides with maximum summer insolation in the northern hemisphere. And yet many of the other insolation maxima only trigger minor warming events, and so interglacials only occur after four or five insolation cycles. No generally accepted explanation exists for this peculiar intermittent climate response, and any comprehensive explanation for ice age modulation and periodicity has to be able to explain this anomaly.

The answer to this conundrum can be found in a novel reanalysis of the effects of decreasing atmospheric CO2 concentrations during an ice age. Ice age CO2 reductions coincide with an increase in ice sheet extent and therefore an increase in global albedo, and this should result in further cooling of the climate. But what actually happens is that when CO2 reaches a minimum and albedo reaches a maximum, the world rapidly warms into an interglacial. A similar thing happens during an interglacial, where high CO2 and low albedo results in cooling. This counterintuitive response of the climate system also remains unexplained, and so a hitherto unaccounted for agent must exist that is strong enough to counter and reverse the classical feedback mechanisms.

The answer to both of these problems lies in glacial dust, which was deposited upon the ice sheets towards the end of each glacial maximum. Previous research has considered two effects of this aeolian dust on the glacial climate: the increased albedo of atmospheric dust cooling the climate, and the mineral fertilization of marine life reducing atmospheric CO2. But both of these effects would result in a cooling feedback, and therefore provide no explanation for the interglacial warming that appears to result from dust deposition. In great contrast to these explanations, what actually happens is that during the glacial maximum, CO2 depletion starves terrestrial plant life of a vital nutrient and causes a die-back of upland forests and savannahs, resulting in widespread desertification and soil erosion. The resulting dust storms deposit large amounts of dust upon the ice sheets and greatly reduce their albedo, allowing a much greater absorption of insolation. Up to 180 W/m  2 of increased absorption can be provided to the northern ice sheets, when calculated seasonally and regionally instead of annually and globally.

This dramatic increase in insolation and absorption results in melting and dissipation of the northern ice sheets, and the establishment of a (short) interglacial period. Ice ages are therefore forced by orbital cycles and Milankovitch insolation, but regulated by ice-albedo and dust-albedo feedbacks. And the warming effects of dust-ice albedo are counterintuitively caused by a reduction in global temperatures and a corresponding reduction in CO2 concentrations. And while this proposal represents a complete reversal of conventional thinking it does explain each and every facet of the glacial cycle, and all of the many underlying mechanisms that control its periodicity and temperature excursions and limitations.


Full paper on Academia . edu
Modulation of ice ages via Precession and Dust-Al bedo Feedbacks
https://www.academia.edu/20051643/Modulation_of_Ice_Ages_via_Precession_and_Dust-Albedo_Feedbacks

Edit:
New, shorter, easy-read version of the paper uploaded.


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« Last Edit: January 06, 2016, 08:51:53 PM by ralfellis »

Neven

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Re: Modulation of ice ages via dust-ice albedo
« Reply #1 on: January 01, 2016, 10:56:03 PM »
Welcome, Ralph. I've moved your topic over to the Science category because I think it fits in better here. I'm sorry I can't comment on your interesting theory, as I know very little about the subject. But I'm sure others know more.
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bbr2314

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Re: Modulation of ice ages via dust-ice albedo
« Reply #2 on: January 02, 2016, 03:37:23 AM »
This was a fantastic read and if I may, I have two questions:

1) What do you think this implies re: our current state, and what are current dust concentrations vs. historic values?

2) I think I'm most confused as to how CO2 increases once it hits the minimum. Once the planet starts to warm, perhaps it is just volcanic eruptions/etc that inject more into the atmosphere, gradually increasing concentrations until plants begin taking more out vs. what's in? I think this probably has a response elsewhere on the internets and I'm forgetting the reason why it happens at the moment.

3) Sea ice is not addressed here, but I'd imagine its role would differ substantially from land ice, as its seasonal temporality means it is much more likely to maintain a higher albedo vs. a dirty glacier. I'd imagine incorporating paleo extent reconstructions could further improve this research.

bbr2314

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Re: Modulation of ice ages via dust-ice albedo
« Reply #3 on: January 02, 2016, 05:09:35 AM »
After careful thought, I would like to add an addendum to the above wrt importance of sea ice --

Perhaps an increasing contrast between sea ice and the snowpack on land is also a crucial factor in the flip between cold and warm? If the differential between land and snow is sufficient, then it would follow that a filthy Greenland contrast against a relatively pristine Arctic or CAA/Hudson Bay would result in the same kind of contrast but over water rather than land, resulting in stronger LPs and more precipitation.

ralfellis

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Re: Modulation of ice ages via dust-ice albedo
« Reply #4 on: January 02, 2016, 04:45:22 PM »
Welcome, Ralph. I've moved your topic over to the Science category because I think it fits in better here.

Thanks for letting me post.  I hope the topic proves interesting.

Ralph

ralfellis

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Re: Modulation of ice ages via dust-ice albedo
« Reply #5 on: January 02, 2016, 05:17:07 PM »
This was a fantastic read.

Glad you liked it.  It has taken a lot of thought and research across a range of subjects.


1) What do you think this implies re: our current state, and what are current dust concentrations vs. historic values?

I did read that modern dust concentrations were about 10% of LGM dust levels. But if modern concentrations contains a lot more soot, which is 50x more insolation absorbent, it will still have a large effect on the ice sheets.   

However, we are not in a Great Summer at present (more like a Great Autumn) so insolation levels have reduced, and that will reduce any effects.  And we should stay in a Great Autumn for the next 100 kyr or so, so there should be no new ice age for a long time.  I shall be looking more into the modern reaction of the ice, as it does have a bearing on my calculations as well as the modern climate. 



2) I think I'm most confused as to how CO2 increases once it hits the minimum. Once the planet starts to warm.

We have not addressed that issue too much, as it is enough to know that CO2 and temperature are highly correlated. The best guess at present is that this is simply oceanic solubility, with cooler water absorbing CO2 and warmer water outgassing it. The upper layers of the oceans should only be responsible for a 30 ppm change in CO2, which is why there has been a search for other explanations.  But I don't really buy the idea of marine organism sequestration, because all that CO2 has to come back out of the oceans within just 5,000 years of an interglacial warming.

My best guess is that there is greater interaction with lower oceanic levels than currently thought, and the CO2 is stored there. (If so, then this may be one component of modern CO2 level rise. A tropical temperature rise of 1Âșc may be responsible for 20 ppm.)  But the methodology of CO2 storage is incidental to this particular paper. It is enough to know that it happens, and it follows temperature.

 

3) Sea ice is not addressed here, but I'd imagine its role would differ substantially from land ice, as its seasonal temporality means it is much more likely to maintain a higher albedo vs. a dirty glacier.

Indeed it would. But I think it is not too much of a generalsation to say that annual winter sea ice is almost a constant. It oscillates every year within certain limits, and it provides the same albedo forcing component every year, so the average influence would be about the same.  There may have been more annual winter sea ice at the LGM, but not that much. The same constraints of air and water temperature would apply as today, just at more  tropical latitudes. 


Cheers,
Ralph




sidd

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Re: Modulation of ice ages via dust-ice albedo
« Reply #6 on: January 05, 2016, 01:20:53 AM »
This article remonded me of another by Petit in but i could not until now find it.

DOI: 10.1111/j.1600-0889.2009.00437.x

looking at it reminded me that vanNes have dust data in the supplementaries

DOI: 10.1038/NCLIMATE2568

sidd

ralfellis

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Re: Modulation of ice ages via dust-ice albedo
« Reply #7 on: January 06, 2016, 08:53:06 PM »

Sidd, that link did not work, can you try again?

Also, I have uploaded a new shorter and easier to read version of the paper.
https://www.academia.edu/20051643/Modulation_of_Ice_Ages_via_Precession_and_Dust-Albedo_Feedbacks

sidd

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Re: Modulation of ice ages via dust-ice albedo
« Reply #8 on: January 06, 2016, 09:16:55 PM »
The links to the papers can be found at http://dx.doi.org by putting in the DOI (digital object identifier, the part following the initial "DOI:" ) into the search field at that site