Support the Arctic Sea Ice Forum and Blog

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Topics - ralfellis

Pages: [1]
Science / Modulation of ice ages via dust-ice albedo
« on: December 31, 2015, 09:07:14 PM »
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.



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

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



Pages: [1]