Guest post by Dr. David Archibald
The Earth is currently in an interglacial period of an ice age that started about two and a half million years ago. The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago. This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow. The first small glaciers were formed in Antarctica perhaps as long ago as 40 million years. They expanded gradually until, about 20 million years ago, a permanent ice sheet covered the whole Antarctic continent. About 10 million years later, glaciers appeared on the high mountains of Alaska, and about 3 million years ago, ice sheets developed on lower ground in high northerly latitudes.
Pacific Ocean bottom water temperatures started declining 40 million years ago, falling 10° C to the current 3° C. The band of high ocean temperatures (above 25° C) also contracted towards the equator, from 45° latitude to 20°. Eventually the oceans lost enough heat that the Earth’s orbital parameters started causing surges in ice formation. There are three orbital parameters: eccentricity, precession and obliquity, shown in Figure 1.
Figure 1: Orbital Parameters: Eccentricity, Precession and Obliquity- click for larger image
This figure is developed from A.L.Berger, 1978, Long Term Variations of Daily Insolation and Quaternary Climatic Changes, Journal of the Atmospheric Sciences, volume 35 (12), 2362-2367.
Eccentricity is caused by changes in the shape of the Earth’s orbit due to the gravitational attraction of other planets. Precession is the change of direction of rotation. Obliquity is the tilt of the axis. When these effects aligned, their effect is reinforced. From three million years ago to about 800,000 years ago, the dominant pattern of glaciation corresponded to the 41,000 year period of changes in the Earth’s obliquity. Since then, a 100,000 year cycle has been dominant.
Ice ages occur because the summer sun in the northern hemisphere does not get hot enough to melt all the ice that accumulates over winter. Ice has a much higher reflectivity than rocks or vegetation, and so reflects more sunlight into space and the cooling is reinforced. Eventually the orbital parameters change back and warming occurs. Glacial periods tend to cool slowly and warm abruptly. Because the Earth’s orbital parameters can be calculated, the amount of sunlight in high northern latitudes can be calculated.
Figure 2: June Mid-Month Insolation at 65° North – click for larger image
This figure is derived from M.F.Loutre and A.Berger, 2000, Future Climate Changes: Are we entering an exceptionally long interglacial?, Climatic Change 46, 61-90
Figure 2 shows how that translates to insolation (sunshine) at 65° North. The recent peak in insolation was 11,000 years ago at the end of the last glacial period. It has since declined by about 10% to 476 watts per square metre. Insolation will rise from here for the next 30,000 years, but it will still be low enough for the next glaciation to form. This is shown by Figure 3 of Northern Hemisphere ice volume for the last 200,000 years and a projection for the next 130,000 years. According to these calculations, the Earth is at the beginning of a 20,000 year plunge into the next ice age.
The reason why the Earth doesn’t respond more rapidly to changes in insolation is due to the retained heat in the oceans, which smoothes the whole process over thousands of years. Over the short term, the oceans are very responsive to changes in solar activity. Figure 5 shows the very strong correlation between the annual rate of sea level rise and solar cycles over the 20th century. The sea level rise of the 20th century can largely be attributed to a more active Sun relative to the 19th century. About 70% of the sea level rise of the 20th century was due to thermal expansion of the oceans, with the rest due to melting glaciers.
Figure 3: Future Glaciation – click for larger image
This figure is derived from M.F.Loutre and A.Berger, 2000, Future Climate Changes: Are we entering an exceptionally long interglacial?, Climatic Change 46, 61-90
Figure 4: The Correlation between Sea Level Rise and Solar Cycles over the 20th Century. – click for larger image
The sea level data is derived from S.Holgate, Decadal rates of sea level change during the twentieth century, Proudman Oceanic Laboratory, Liverpool, UK.
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Above Wally said “One thing to remember in talking about orbital cycles and changes in insolation is that the total amount of energy reaching the surface of the Earth over the period of a year does not change it is just distributed differently.”
Here is a plot of data from the SORCE satellite for earth distance, Total Solar Irradiance. Same timeline as the plot I put up last night showing we might already be past solar minimum, a plot of data for distance 1au.
At earth distance irradiance varies over a year as shown here. (flats on the line is missing data, interpolation by hold)
http://www.gpsl.net/climate/data/TSI_earth_distance_2009-02-24a.png
http://lasp.colorado.edu/sorce/index.htm
Your link does not address Wally’s statement at least if we interpret his “over the period of a year” to mean you integrate over such a period. And, indeed he is correct that changes in the mean annual irradiance are very small. It is just the distribution in time (of year) and location (in latitude) that changes. See Fig. (S3) in this publication by Hansen et al: http://pubs.giss.nasa.gov/abstracts/2008/Hansen_etal.html
Tim Channon (06:08:06) :
Above Wally said “One thing to remember in talking about orbital cycles and changes in insolation is that the total amount of energy reaching the surface of the Earth over the period of a year does not change it is just distributed differently.”
He clearly means by ‘over the period of a year’ the ‘average over a year’ and that does, indeed, not vary [except the 0.1% solar cycle variation]
Here is a plot of data from the SORCE satellite for earth distance, Total Solar Irradiance. Same timeline as the plot I put up last night showing we might already be past solar minimum, a plot of data for distance 1au.
It has this variation every year, so no variation ‘over a period of a year’. I do agree that TSI shows we must be past minimum, F10.7 and cosmic rays show the same: http://www.leif.org/research/TSI-SORCE-2008-now.png
P.S. this plot updates in real time.
At earth distance irradiance varies over a year as shown here. (flats on the line is missing data, interpolation by hold)
I understand that, and also recognize that what I am talking about is probably a relatively minor factor over all, but it is an effect that I don’t see accounted for when they talk about sea level rise due to thermal expansion.
More specifically I am thinking about volume changes due to changes in shape of the basin, not volume changes in the earth.
If you make a container of a certain amount of material in the shape of a hemisphere and make a flat pan shaped container from the same amount of material, the amount of water they can hold will be drastically different due to the geometry of the two containers.
For example:
The average depth of the Pacific basin is 4280 meters, while the average depth of the Atlantic basin is about 3600 meters.
If the assumption is made, that for each unit of spreading of the Atlantic ,results in a similar unit of shrinkage of the width of the Pacific, that would imply that at least for those two oceans, sea floor spreading would reduce the total ocean basin volume as the deeper basin is shrinking in size, while the shallower basin in increasing in size.
If you increase the size of the Atlantic basin by some slice of X width near the center of its basin and shrink the Pacific basin by the same width near the center of its basin, the difference in their average depth would amount to a reduction in volume of the combined basins of about 18% of the volume of the Atlantic slice.
In a practical every day situation you can see this sort of thing if you fill a plastic sink liner used for washing dishes with water while it is resting on a flat surface. If you then pick it up, the center of the plastic basin sags under the weight of water it holds. Now the basin is no longer full to the brim since its geometry has changed. If you set it down on an uneven surface so the container distorts, it will overflow.
Basically I am contending that there is an unspoken assumption implied in the sea level change due to temperature discussion, that the shape (and therefore volume) of the worlds ocean basins are constant (at least on short time scales like year to year or decade to decade).
I am suggesting that that is not a valid assumption. At the very least, you have basin volume changes due to the differences in basin average depth and continental drift, as mentioned above. You also have continuous siltation which is constantly trying to fill the basins.
At the outlets of all the major rivers, you have large silt deposits each flood season, plus the displaced volume of wind blown dust which falls into the oceans each year due to wind erosion, and the beach material washed into the margins of the oceans each year due to beach erosion.
In even an entry level physical geography class when they discuss land changes they talk about the evolution of lakes as they gradually silt up, transition to wet lands and eventually turn into a meadow with a river running through it over time. Obviously the oceans will not “fill up”, but the shape of the ocean basin cannot be assumed to be static in my view.
In the case of the Christmas 2004 Tsunami it has been reported that it was generated by very large uplifts of the sea floor in the quake epicenter area of 15-20 meters. The total volume displaced I have not been able to find a number for yet, although this web page mentions the 15-20 meter uplift and the length of the rupture was some 1200 km long.
http://www.itc.nl/library/Papers_2005/tsunami/Earthquake.pdf
In the Yangtze river, it carries enormous silt loads, estimated at 60% by weight in places. The best number I have found is about 1.4 billion tons are carried to the sea annually in this river alone. That would equate to something in the neighborhood of 6.4 x 10^9 cubic meters per year if my ball park calculations are accurate for this single river. If a 1 mm sea level rise is about 3.61 x 10^11m^3, then that would imply that siltation from the Yangtze river each year accounts for about 1% of the annual sea level rise of 1.8 mm per year.
The above calculations were based on the silt having a density of 2.2 gm/cm^3 the same as silicon dioxide.
Since I do not normally work with this sort of calculation, I welcome anyone to double check these back of the envelope calculations.
Larry
The assumption that ice-cap melt volume divided by total ocean area gave sea-level rise would work in a metal bath tub, but the ocean ain’t like that. Hope to see more on this.
The idea of the conservation of volume would not necessarily apply in this case… as the Indian sub-continent continues to move north into the Asian plate, new ocean space is being created at the expense of the atmoshere…i.e. the Himalayas are growing at the same time the Indian Ocean expands ( or Bay of Bengal, Arabian Sea, etc.). The point being that new ocean volume can be created.
What role does accretion of mass from space do to the level of the oceans? Is the accretion significant enough to measurably affect seal level rise?
http://www.expanding-earth.org/page_10.htm
Correction- “sea level”
It looks like accretion would only amount to about 1/18000 of the mass of the annual silt from the Yangtze river. So in and of itself over short time scales it appears to be of not concern.
However if you sum up all these basin filling processes you might come up with a significant fraction of the annual sea level increase.
There are 165 rivers in the world with lengths over 1000 km. The Yangtze is probably the dirtiest and only amounts to about 1% of the global sea level rise, but if you add up the siltation from all those rivers it could be more sizable.
Just to grab a number out of the air, suppose those 165 rivers on average each had 15% of the silt load delivered to the ocean each year as the Yangtze did, you now have accounted for somewhere in the neighborhood of 25% of annual sea level change being accounted for by siltation. Obviously this is just a grab a number out of the air calculation, but it shows that it is not seem unreasonable to assign a fraction of annual sea level rise to ocean basin capacity changes due to siltation and dust accumulation in the oceans.
Larry
Thanks Larry. That does make sense. So, of the 3 mm or so annual rise of the sea level, about 70% is due to thermal expansion and that sedimentation (from all sources) and plate tectonics could account for a significant portion of the remaining 30%. Therefore it seems that the sea level increase brought about by about ice melt is hardly the man made disater that Al Gore et al would have us believe. Why does that not suprise me?
I would not be willing to say that is a fact yet only that I have made a case for a proper analysis of that mechanism by someone who has access to the data and time to properly compute the annual contribution to sea level rise by mechanisms other than thermal expansion.
I am simply stating that on a first blush examination it is not unreasonable to suppose that this is at least one other mechanism that could account for a percentage of the change, but my off the top of my head ball park calculations certainly do not in any way establish a value for that contribution, but only give me reason to speculate that it might be worth while to investigate.
Larry
Have you seen the pictures of the Titanic, Bismark or Hood?
All three ships are being covered with gloop (a technical term), a mixture of organic material, derived from atmospheric CO2 and N2 and newly precipitated minerals. We know when these ships when down and we know how much gloop there is.
Here is a pic of the Titanics out propeller, made of bronze and not subject to corrosion.
This wing propeller is 23.5 feet (7 m) in diameter and weighs 38 tons (34 t).
http://titanicmodel.com/photoarchive/titanic/wreck/fullsize/image13.jpg
here in an anchor chain,
http://titanicmodel.com/photoarchive/titanic/wreck/fullsize/image24.jpg
Some idea of the size.
http://www.titanic-model.com/articles/anchor/titanics_center_anchor.htm
How much gloop is there in 90 years ?
My guess is about 1 cm in 90 years. The Earth is biotic.
Here are a few more figures I just found on ocean sedimentation.
http://www2.ocean.washington.edu/oc540/lec02-2/
http://www.ngdc.noaa.gov/mgg/sedthick/sedthick.html
http://www.odp.usyd.edu.au/odp_CD/oceplat/opindex.html
It looks like the data is out there but would take someone a considerable amount of time to digest and analyze.
From:
http://www.waterencyclopedia.com/Oc-Po/Ocean-Floor-Sediments.html
Larry
hotrod: Whew, lotsa numbers there. But on a couple things:
“…More specifically I am thinking about volume changes due to changes in shape of the basin, not volume changes in the earth….” Interesting, worth investigating. Years ago I had a speaker to a forum talking about the Cretaceous. He said it was a time of unparalleled rapidity of spreading (NAm was scooting away from Africa, and SAm had begun to move, too. Consequently or coincidentally the K was a time of great epicontinental seas covering big chunks of NAm, Africa and maybe elsewhere. The Mid-Atlantic Ridge must have been bulging, and Atlantic sea floor, at any given distance from the MAR would have subsided less than in a more ordinary rate of spreading. And presumably those rapidly westward-moving plates were overriding deeper Pacific oceanic sea floor.
Long story short: yes I think it’s possible for plate tectonics to affect the sea basin volume and thus sea levels. Which way they’re working today, I couldn’t hazard a guess.
On the Indian Ocean (IO) uplifts attendant on the tsunami-generating seism, let’s agree that it was 100 meters uplift by 5 KM wide by 1200 KM long. That gives us (0.1x5x1200) km^3 in volume = 600 KM^3. The IO has a volume of 292M KM^3 (wikipedia). So the delta volume is 600/292M = .0002%. Does this calculate to a measurable increase in sea level? And remember, in dealing with with faults, something is moving up – and something is moving down or being attenuated somewhere. Google “rift and graben”. There is no new volume created – just things adjusting up, down or laterally.
hotrod – re “check the numbers”.
“In the Yangtze river, it carries enormous silt loads, estimated at 60% by weight in places. The best number I have found is about 1.4 billion tons are carried to the sea annually in this river alone.”
Let’s agree 1.4 x 10^9 tonnes of solid matter get carried to sea. This is deposited as grains of silt and flocculated clay particles and so on in an initially not very dense aggregate. Let’s say the deposits have a s.g. of 1.65 g/cc (2.3 g/cc solid, 1.0 g/cc H2O, 50:50).
Then 1.4×10^9 tonnes x (1×10^6g/tonne) = 1.4×10^15 g x 1cc/1.65g = 8.5×10^14 cc. A kilometer cubed is 1×10^15 cc. So we get 8.5×10^14 cc x (1km^3/1×10^15cc) = .85 km^3 of new material deposited in the Yangtse delta annually. That’s not much, and it will get denser as time goes on as water is ultimately squeezed out.
Please check my math!
David Archibald has transferred the correlation of insolation changes with glacial change from his main reference source* and overlaid his own interpretation.
* http://www.dvgu.ru/meteo/library/243887.pdf
The originating source reflects mainstream understanding on the contribution of insolation changes to glacial change (triggering other processes like atmospheric changes and albedo). Dr Archibald has dismissed the findings of that paper, which are quite different from his own, but has not explained why he has done so.
As Dr Archibald’s above thesis is purely correlative, and not in disagrement with this superficial part of the originating paper, there is a significant argument missing here.
Specifically, Loutre and Berger posit that insolation changes are too weak by themselves alone to account for past glacial changes. This is entirely consistent with virtually all the modern literature on the matter (referenced in the study). Yet Dr Archibald seems to contend, with no references, meaningful calculations or descriptions, that insolation changes are alone strong enough to cause the glacial changes. His thesis is consistent with the scientific literature regarding correlation with orbital variaton/insolation changes. I cannot fathom why he ignores/dismisses the rest of the science on the subject of glacial change.
I note with disappointment that Dr Archibald has referred to Berger and Loutre in the comments above as “loonies”. As this is an ad hominem remark (ie, a slur devoid of any argumentation to buttress it) I now wonder if Dr Archibald is a serious scientist qualified in the field he has undertaken to weigh in on.
Thanks for the check Jim! It has been a long time since I worked with scientific notation, and I think you are correct. It looks like I dropped a decimal place doing my quick calculation, and was off by a factor of ten using my assumptions.
On reworking it with 2.2g/cc density as I did the original, I came up with 6.3636 x 10^8 cubic meters rounding to 6.4x 10^8 cubic meters, rather than my original value of 6.4 x 10^9 cubic meters, or about 0.00176278 of 1 mm sea level rise which would be about .1% , not 1% of an annual sea level rise of 1.8 mm which was the number I was working with.
I must have dropped a decimal point some place. Thanks for the check!
That change would drop the effect of sedimentation to a minor contributor to annual sea level rise.
It just bothers me when no one even mentions a mechanism like this. I would much rather have them work the numbers and then state it was of negligible effect.
Years ago I worked as an emergency planner and my job basically involved looking for the unstated assumptions or pointing to the 600 lb gorilla in the room no one wanted to talk about. As a result, my first instinct when looking at a problem, is to brain storm every possible other explanation and then start eliminating them one by one to see if one of them refuses to go away.
Larry
My understanding is this specific type of rebound of a stressed plate would result in the subsidence of the above sea level portion adjacent to the fault (the island of and the sudden upward thrust of the subsurface plate, as shown in the following video.
http://www.iris.edu/hq/programs/education_and_outreach/aotm/5
No single event like that probably would have a very large effect, although it would be interesting if there was a detectable step change in world wide sea surface height measurements. I was speculating on the over all stability of the shape of the basin, with this as an example of some of the distortions that might be taking place along the ring of fire due to thousands of small earth movements.
In the case of the Good Friday 1964 earth quake in Alaska, they estimate total displacements underwater were on the order of 120 cubic kilometers.
http://www.drgeorgepc.com/Earthquake1964Alaska.html
It is not clear what the net change in undersea volume was, as some of the changes were uplift and some were subsidence, some areas effected were submerged and others were above sea level prior to the quake.
As mentioned in my other post, I am just brainstorming about alternate mechanisms I have not seen discussed much in the context of world sea level changes.
Larry
Re Abuliam (12:23:52) :
Sorry but it’s not that simple, as the Indian plate keeps moving north and ppushing up the Himalaya, the latter is being eroded and filling out the Indian ocean. The Ganges fan is the largest accumulation of submarine sediments on Earth.
“David Archibald has transferred the correlation of insolation changes with glacial change from his main reference source* and overlaid his own interpretation.”
I’m not allowed to use your data, possibly for another issue than that for which you gathered same, and come to a conclusion differing from yours?
Whatever.
One intriguing problem associated with orbitally driven glacial cycles is the transition from 41,000-year to 100,000-year climatic cycles that occurred without an apparent change in insolation forcing
It didn’t. It changed from 1*41kyr to 2, 3 or 3*41kyr, probably caused by the connection of the Americas, bringing more moist (snow) to the high north.
And the interglacials last 1 mill. years have never survived an obliquity minimum so why would it this time?
argh, 1,2 or 3*41kyr.
gary gulrud says:
You are certainly allowed to, but it seems like the least you should do is explain clearly what the other person’s interpretation was and why you interpret it differently.
barry says:
Here is one piece of information that I found on him ( http://www.sourcewatch.org/index.php?title=David_Archibald ):
Perhaps Dr. Archibald can fill us in with more detail on his qualifications and publications in the field.
In the introduction to this thread, David mentioned that that bottom water temperature of the Pacific Ocean started declining 40 million years ago, falling by 10C from 13C to the current 3C level. A number of posters have queried this assertion; Harold Ambler (07:30:40); Steiner Midskogen (09:29:52) 23022009 & Ed Zuiderwijk (05:39:12) 24022009, but to date I don’t think that their concerns have been answered.
Oxygen can only be produced by sunlight. At the bottom of the ocean there is no light source, other than the very faint bioluminescence powered by chemical reactions, and so no oxygen gas can be formed. In the ocean, oxygen is created in the surface waters, where sunlight allows marine algae to photosynthesise in the euphotic zone and storms, that produce breaking waves, permit atmospheric oxygen to mix in. The presence of oxygenated water at oceanic depths in the aphotic zone requires a process of gas transport and replenishment throughout the water column. Thermohaline circulation is the mechanism by which the world’s ocean waters overturn and the process by which oxygenated water reaches the ocean depths.
Throughout millions of years of geological history, the overturn of the world’s oceans has operated in one of two modes, either the “Haline” mode of mid-latitude warm water oceans or the “Thermo” mode of polar cold water oceans. In the Jurassic and Cretaceous eras the haline mode of ocean water overturn dominated. The world was warm and so the bottom waters the oceans were warm also. During the Cenozoic era, since the Paleocene-Eocene Thermal maximum 55 million years ago, as the world has cooled and Antarctica has become an ice continent, the cold thermal mode of ocean water overturn has prevailed.
Haline circulation is a warm world process, it relies on the creation of dense saline water in mid-latitude oceans where evaporation exceeds rainfall, it dominates today only in the waters of the Mediterranean. The Mediterranean Sea occupies an enclosed series of basins. Its waters experience high temperatures in summer and insufficient input of river water from Southern Europe and the Nile, to maintain the total seawater mass balance.
Because of the loss of water to the atmosphere through evaporation, the Mediterranean Sea is more salty than the adjacent Atlantic Ocean. If it wasn’t for the continuous surface influx of new ocean water through the Gibraltar Strait, then the Mediterranean Sea would eventually dry out. In the past the Mediterranean, with an area of 2.5 million sq kms, did indeed greatly reduce in size, as the presence of deeply buried canyons of the ancient River Nile and River Rhone testify. In addition, seabed boreholes in the abyssal plains of this small ocean prove the presence of ancient thick salt layers. Think Dead Sea, but two and a half thousand times bigger.
Today the Mediterranean Sea exports its salty water back into the Atlantic Ocean through the Gibraltar Strait as a dense bottom water counter-current. This warm saline-rich water falls under gravity to depth in the Atlantic, but does not now reach the abyssal ocean plain. Instead it floats at depth above the denser 3C, polar ocean derived, bottom waters of the modern cold water world.
Doug Janeway (07:13:14) :
“The Earth’s current ice age is primarily caused by Antarctica drifting over the South Pole 30 million years ago. This meant that a large area of the Earth’s surface changed from being very low-albedo ocean to highly reflective ice and snow. “
Incorrect. Antarctica was already moving into the Antarctic circle some 125 million years ago, and it was at the South Pole during the Early Cretaceous about 120 million years ago. Although Antarctice experienced cool temperate conditions with winter snowfalls and icing and very limited periods of small permanent polar ice caps, much warmer conditions free of polar ice caps dominated from the Late Cretaceous 117mya to the onset of the latest ice ages about 30-32mya. In other words, Antarctica was located at the South Pole for tens of millions of years without causing an ice age and polar galciations to occur.
There were species of of dinosaurs and flora adapted to nocturnal habits well suited to the six months of darkness prevalent in an Antarctic in the antarctic circle.
foinavon (15:03:17)
Thank you so much for your generous response to my post. I really appreciated your comments and the inclusion of the abstract. That said, I hope that you will not take it as ungracious of me if I pose a few questions.
You describe the transition from a 41,000 cycle to the 100,000 cycle as beling something like missing a “pulse” while the abstract describes it as more of a gradual transition. Is this a situation where there isn’t enough good data available, so that a certain amount of speculation is necessarily involved in arriving at such conclusions? My limited reading on the subject has not included research findings that describe intermediate length cycles. I think that this is a key issue and that your “pulse” notion is more nearly correct. But on the other hand, I wonder if the growth of more extensive ice sheets isn’t more likely to be an effect of an X factor(s) rather than the cause of the sudden shift from a 41,000 cycle to a 100,000 cycle.
Am I correct in recalling from my reading that interglacial periods have extended for of a failry similar time periods? If so, this would support the notion that the earth has been in a prolonged cool phase for the past 20 to 40 million years, with recurrent heat cycles being introduced (for largely unknown reasons) periodically. The coolness includes but is not necessarily dependent upon glacial conditions. For example, the Andrill project of a few years ago found that the earliest indication of a collapse of the Ross Ice Shelf in Antartica dates back about 17 million years. This seems like evidence of a ing phase occurring during a non-glacial period of the prolonged (still going) period of cold.
From this “heat clcyes” notion I suggest that unknown factors might have pushed the 15.000 to 20,000 year recurring warm phase (which accounts for the interglacial periods) into a 100,000 cycle, and that in turn wouild have caused much increased growth of the ice sheets. These heat cycles that I propose also seem to regularly warm things up a bit beyond our current Antarctic regional (or possibly global) temperature, in that the Andrill pras reported in Science the Scott Ice Shelf has apparently been warmed to the point of collapsing some sixty times or so in the past 17 million years..
******
barry (22:13:52) :
Specifically, Loutre and Berger posit that insolation changes are too weak by themselves alone to account for past glacial changes. This is entirely consistent with virtually all the modern literature on the matter (referenced in the study). Yet Dr Archibald seems to contend, with no references, meaningful calculations or descriptions, that insolation changes are alone strong enough to cause the glacial changes. His thesis is consistent with the scientific literature regarding correlation with orbital variaton/insolation changes. I cannot fathom why he ignores/dismisses the rest of the science on the subject of glacial change.
******
As you say, Loutre and Berger are running a model (BTW, it does seems interesting). For their model, they use a CO2 sensitivity of 2C for a doubling. Their results obviously depend on this sensitivity. This sensitivity is disputed by many. Empirical data suggests it is lower — as low as .5C or lower for a doubling.
They should have run their model w/a range of CO2 sensitivities to compare the results.
“Perhaps Dr. Archibald can fill us in with more detail on his qualifications and publications in the field.”
How about your Curriculum Vitae Joel?