Guest Post by Willis Eschenbach
A WUWT commenter emailed me with a curious claim. I have described various emergent phenomena that regulate the surface temperature. These operate on time scales ranging from minutes to hours (e.g. dust devils, thunderstorms) to multi-decadal (e.g. Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation). He suggested that there is also a much slower thermostatic mechanism at play over thousands of years and longer. Here’s how I understand it.
He said that when it gets warmer, the atmosphere is more moist, so there is more snow on Antarctica. This translates into more ice on the ice cap, which puts increased pressure on the ice below. Now, the ice gain at the surface and the ice loss in the calving of the Antarctic glaciers is in some kind of long-term very slow-moving steady state. Pressure at the top squeezes out the ice on all sides. So increasing the ice mass over time would lead to more calving, which in turn would cool the surrounding ocean. He said this slow process shown below functioned as a long-term factor promoting thermal stability.
Warming –> increased Antarctic snowfall –> thicker ice cap –> increased iceberg calving –> cooling
He suggested I should look into the rate at which the ice has historically accumulated at the Vostok ice core location in Antarctica. He thought that the ice accumulation rate was a function of temperature. His idea was that Vostok shows that increased temperatures lead to increased antarctic snowfall, which in turn increases the rate at which the ice accumulates on Antarctica. So I took a look.
The ice core from Vostok is a technological marvel. They drilled 3.3 kilometers (two miles) straight down into the ice, and extracted a core of undisturbed ice. Then they analyzed it one metre by one metre, along the entire length of the core. The variations in temperature calculated from the core are well-known, they show the history of the last four ice ages:
Figure 1. Temperature record from the Vostok ice core. The zero point on the temperature scale is modern-day temperature. Temperature is calculated from the variations in the 18O oxygen isotope as recorded in the ice core. Present-day values are at the left of the graph. DATA SOURCE: NOAA Paleoclimate
Here, you can see the ice ages, interrupted by short periods of warming … well, short by geological scales at any rate. The most recent warm period, on the left, has lasted about 10,000 year (10 kya). (As an aside, for me the mystery is not what it was that slowly and gradually pushed us into each ice age with lots of fits and starts. The thing that perplexes me is what it was that abruptly yanked us out of each ice age in one extremely fast period of great warming. But I digress …)
Although I had seen that before, I’d never looked at the ice accumulation rates. Figure 2 shows the annual rate of accumulation of ice at Vostok.
Figure 2. Ice accumulation rate record from the Vostok ice core. Since the measurements are taken every metre along the ice core, the accumulation rate is calculated as the reciprocal of the age differences from one measurement to the next. Present-day values are at the left of the graph.
Urg. That was not too appealing. Clearly, what we are seeing is the progressive compression of the ice layers as we drill deeper and deeper into the ice cap. Millions of tonnes of ice on top have progressively flattened the deeper layers. Makes it hard to see any relationship. I considered various ways to model the compression of the layers and remove it … and discarded them all.
What I did notice, though, was that as we see at the left hand end of the graphic above, new snow is fairly bulky. But it gets compressed quite rapidly at first. After that initial rapid compression of the snow into ice, however, the compression is somewhat linear from that time onwards. So I decided to omit that first part of the data, which is about five thousand years. I then plotted up the remaining ice accumulation data, and I included the temperature data on the same graph so I could compare them.
Figure 3. Ice accumulation rate record (blue) and temperature record (red) from the Vostok ice core. Both records start a 5000 years before present. Recent values are at the left of the graph.
Dang … surprisingly, his claim was looking much, much better. So I took a first cut at modeling the ice accumulation rate from the temperature data. I’ve included the depth as a second explanatory variable. Here is the result of the estimation of the ice accumulation rate as a function of depth and temperature:
Figure 4. Ice accumulation rate record (blue), temperature record (red), and estimated ice accumulation rate based on temperature and age (black) from the Vostok ice core. All records start at 5000 years before present. Recent values are at the left of the graph.
Now we’re getting somewhere, but there is still a problem. Because the layers are progressively flattened with depth, the response of the ice accumulation rate to temperature is also progressively flattened with depth. To allow for this, I included the product of the two variables (depth and temperature) in the analysis, giving the following result:
Figure 5. Ice accumulation rate record (blue), temperature record (red), and estimated ice accumulation rate based on temperature, age, and age*temperature (black) from the Vostok ice core. All records start at 5000 years before present. Recent values are at the left of the graph.
Well, there you have it. Ice accumulation in Antarctica is assuredly a function of temperature. What’s not to like? His hypothesis is obviously correct. Done and dusted, right?
Well … in a word, no. I didn’t like it at all.
The problem that I had with the good fit is an odd one … the fit is too darn good. Nothing in nature fits that well, down to the tiny wiggles in the blue and black lines at the right of the graphic. Correlations that good make my nose twitch, they set off my bad number detector..
I had started with the raw data and no preconceptions. Now I knew what I was looking at and looking for, so I went off to research what might explain it. To do that, I looked at the various methods for dating an ice core. Turns out there are four of them—count the annual rings, align to known events, radioactive dating, and use a “flow model”. Problem is that the first three methods only get us back about 80,000 years into the past. Beyond that, it’s all flow models. Which is OK, and they are likely fairly accurate. The problem lies elsewhere, in the input variables to the various flow models. Here’s the list of what goes into the models:
- Temperature
- Ice thickness
- Flow patterns
- Gross accumulation rates
- Ice rheology, the study of how much ice deforms and moves in response to pressure.
I’m sure you can see the problem. In my calculations, the net accumulation rate shown in blue above is a function of the age change per metre of ice core. Makes perfect sense, that’s how you calculate it. If it takes a hundred years to add a metre of ice, the accumulation rate is equal to 1 metre / 100 years = 10 mm/year.
The problem is that in their model, the age change per metre in turn is very much a function of the temperature. And that means that we expect the net accumulation rate to be a function of the temperature. It is inherent in the calculation—accumulation is a function of age, and age is a function of temperature, so accumulation is a function of temperature.
As a result, the graphs that I have shown above have very little inherent meaning. It’s like showing that one equals one. The commenter was correct that he found a correlation … it just didn’t prove anything.
This also means we cannot use the correlation above to support the commenter’s theory that increased temperature leads to increased accumulation rates.
However, all is not lost. This analysis does point out one important thing—the best judgement of the scientists studying the question is that indeed, ice accumulation rates in Antarctica are strongly positively correlated with temperature. They say that counterintuitively, a warmer world indeed means more Antarctic ice.
So … IF the scientists are indeed right, then this analysis also allows for a couple more deductions. One is that near the surface, which is to say near the present, the depth and depth*temperature terms of the estimate are small. This means that the recent annual addition of snowfall to the icecap is about 20 mm (of ice equivalent) per year. The change in that accumulation rate per degree of warming is about 1.25 mm/year This implies that for each additional °C of warming, the accumulation rate goes up/down by about 6%.
The graph also shows that during the end of the most recent ice age, the annual accumulation rate was only about half of the current rate.
All of which would suggest that the change is large enough to support the idea of a slow restorative force opposing any change in temperature. Since at the start of an ice age the annual addition to the icecap drops rapidly to as low as 50-60% of its previous value, surely that much of a decrease in ice accumulation must result in a correspondingly reduced amount of iceberg calving at the ocean.
How much energy is involved in the change? Well, to first melt and then evaporate a cubic metre of ice takes about 90 watt-years of energy. The change in accumulation rate between ice age and interglacial is about 10 mm/year, which is about a metre per century difference.
This means that the change in energy between ice age and interglacial due to the variation in ice buildup is about 0.9 watts per square metre constant change over the surface of Antarctica. This is a fairly small effect.
However, in contemplating this situation, I realized that one oddity of this method of moving latent heat around in the form of ice is that the ice is added over two dimensions, over the surface area of Antarctica. But at the other end of the process, the ice is squeezed out in one dimension, along the coastline. Given the relative area (11.1E+6 km^2) and the coastline length (18.0E+3 km) of Antarctica, this is a concentration of about six hundred to one. This means the 0.9 W/m2 across the continent becomes about 0.9 * 618 ≈ 550 watts of heating or cooling per metre of coastline. This variation in iceberg calving rate represents a strong local change immediately adjacent to the coastline.
Next, let’s consider what this variation in ice calving rate along the Antarctic coastline does. The key underlying concept to keep in mind is that vast amounts of heat are being exported constantly from the tropics to the poles, where the heat is radiated into space. The transportation is done by both the ocean and the atmosphere, both of which move heat polewards 24/7.
As a result, the rate at which the planet can lose energy is constrained by the speed of the oceanic and atmospheric circulation. The general rule is, anything that speeds up oceanic circulation will cool the planet down, and vice versa.
The circulation around Antarctica is shown below.
Figure 6. Circulation patterns around Antarctica (right side of drawing).
Setting the details aside, the takeaway message from this graphic is that when the Antarctic coastline gets more ice input from the glaciers, the speed of the circulation increases because more cold water is sinking downwards around the continent.
And on the other hand, when there is less ice around the Antarctic coast the circulation will slow down. There will be less cold water to drive the downwelling leg of the thermal circulation.
So the entire feedback loop looks like this:
Warmer southern ocean –> wetter atmosphere –> more snow on Antarctic interior –> more glacier calving around Antarctic perimeter –> increased oceanic circulation –> increased global cooling.
Anyhow, that’s what I found out today. Of course, your conclusions from the same facts may be totally different …
Regards to everyone,
w.
My Usual Request: If you disagree with me or anyone, please quote the exact words you disagree with. I can defend my own words. I cannot defend someone else’s interpretation of some unidentified words of mine.
My Other Request: If you think that e.g. I’m using the wrong method on the wrong dataset, please educate me and others by demonstrating the proper use of the right method on the right dataset. Simply claiming I’m wrong doesn’t advance the discussion.
EDIT: Willis accidentally left figure 6 out of the body of the text, but made it the featured image for the post from the set of images he uploaded. I’ve corrected that problem – Anthony
Missing Figure 6 ?
Figure 6 has been restored, see note at end of essay
The warming of the Arctic (and large ice-free areas) would also provide the humidity necessary to form over one-mile-thick ice sheets to cover all of what is now Canada. An ice-free Canada is apparently an unusual state during the current ice age, the past 2.6 million years.
Indeed, for the last million years or more, most of Canada has been buried under a mile of ice. Pretending that Ice Ages will never happen again is part of the global warming dogma. It is also quite unbelievable since we still don’t know what there is causing this ticking clock of severe Ice Ages/sudden dramatic warmups/severe ice Ages.
“Pretending that Ice Ages will never happen again is part of the global warming dogma.” Even worse, it is common knowledge the Earth is in an Ice Age, we are living it now, but they ignore that fact. Part of the confusion they rely on comes from improper use of the term “ice age” when “glacial period” is actually meant. What CAGW theory amounts to is an end to the Ice Age, melting of the Arctic sea ice, Greenland ice sheet and, the biggy, all the ice at the South Pole. And beyond that, whatever ginormous forces of Nature have caused the steady cooling of the planet since the Eocene resulting in the present Ice Age…humans are now cancelling that out and reversing it by burning fossil fuels. Extraordinary claims require extraordinary proof.
Tick, tock, tick, tock, tick, tock … BOOOM! For the average plebe especially one living somewhere with crummy distribution “Boom” would mean … “you die.”
@Robert:
Yes, we are presently in an ice age, having a short interglacial.
W. used the term ‘ice age’ as it is commonly, but innacurately, used.
I usually say “ice age glacial” as a kind of compromise between the two modes of speech.
It is very important, though, to remember that a few thousand years of warm interglacial is NOT the end of an ice age, just a natural and expected warm excursion. Real climate change, all natural.
We WILL drop back into an ice age glacial, and very soon in geologic time. No more than about 2000 years (so about as much time as since Rome ruled Judea and that Christian thing started) or perhaps as short as about 300 years (think founding of North American British colonies). It is also remotely possible we entered the process in the Little Ice Age and are just having a tiny wobble to warm on our way down already. (It isn’t a linear process, and has large excursions, but is so slow we don’t notice much in any one lifetime)
Those warm spikes have a name too. Interstadial. Lots of them have happened.
https://en.m.wikipedia.org/wiki/Stadial
The null hypothsis ought to be that the present warm is just a natural Interstadial, the LIA was a stadial, and the pattern is towards more cold in each stadial, where they mark our decent into the modern glacial in our present ice age.
All that insight lost when one forgets we ARE in an ice age wobble of very brief warmth.
Hi Willis, thanks for this post. I had earlier received this comment from an Australian paleontologist, currently looking for fossils on Vega Island next to the Antarctic peninsula, an AGW believer:
“Steve Salisbury: The increase in sea ice around Antarctica is most likely a direct consequence of the warming Tom Harley. Tightening of the Circum Antarctic currents in the Southern Ocean due to warmer termperate waters in the Pacific, Atlantic and Indian oceans amplify the colder sea surface temps close Anarctica (similar to a positive phase of the Southern Annual Mode), combined with melting of continental and glacial ice that then feeds into the cooler surface waters… thereby increase the amount of sea ice. We’ve been monitoring this situation closely for the last five years.”
I had suggested he was wrong about warming and asked why Antarctic ice was at very high levels!
“Tightening of the Circum Antarctic currents in the Southern Ocean due to warmer termperate waters in the Pacific, Atlantic and Indian oceans amplify the colder sea surface temps close Anarctica.”
It take it that it wasn’t thought out too well. Apart from the typos (and what’s a Tom Harley), it suggests that being in contact with a warmer substance will make something colder. I take it is merely the cold waters are mixing less with the warmer waters.
I think a Tom Harley is a cross between a Tom Collins and a Harley (Harvey) Wallbanger.
Cheers.
So can you run the flow models without temperature? That might be interesting.
And yes, the real interesting bit is the discontinuity at the end of the ice age. Why is it so sharp?
The catastrophic and very sudden fall in temperatures is the entire point: NO ONE knows, exactly, what is going on and why this happens over and over and over again, the same way. I would suggest our local star isn’t as reliable as we want.
You raised a good point and did the start of a calculation on glacier calving in the Antarctic that was raised in a recent WUWT post:
http://wattsupwiththat.com/2016/02/19/colossal-antarctic-ice-shelf-collapse-followed-last-ice-age/
So, 100,000 square miles of ice 1500+ metre thick disappeared over 1500 years meaning 100,000 square miles of ice 1 metre thick melted every year for 1500 years. So what amount of cooling and what disruption to the ocean currents and atmospheric circulaton would that have caused? Rhetoric question perhaps.
There didn’t seem to be any discussion of that in the post but it certainly made me wonder where all that latent heat went – though as I commented in the post, the ocean volume is large. But that volume of ice melt must have had some effect on the atmospheric and ocean circulations. I just don’t have the skill to imagine or calculate it.
Just wondering since you commented on that aspect here:
Thanks for the comments on something I have wondered about for a long time. So many variables to think about. The climate is Gordian knot waiting for Alexander to come along.
There is the comment above from Tom Harley about the ocean currents and how the warmer world means colder waters around Antarctica. Slower mixing of warmer sub-tropical waters with the colder waters means more transport of latent heat from the tropics to the atmosphere, then to the poles. There would not only be larger energy loss to space as it condenses but also more snow/rain. There could also be a larger current flow into the Arctic ocean causing it to warm (the sea-ice extents seem to be oscillating between the two poles) and this is supposed to increase precipitation over N. America.
Gradually, the oceans cool but the ice sheet remaining keeps the planet cool (and dry) through a large albedo.
The glacial period ending suddenly is the difficult part. Maybe its not as simple as currents through the Drake Passage being blocked. It could be the winter sea-ice extent in the SH causing circumpolar current to deviate north, push warm tropical water towards the Arctic ice sheet. If it coincides with greater insolation in summer above 60N, you get a lot of rain, lakes of water in summer and eventually a rapid loss of the ice.
There is evidence of very dry places like the Sahara and deserts in the Levant having periods of high monsoonal rainfall at the end of the last two glacial periods. Probably need evidence of warmer seas in the south-eastern parts of the oceans in cooler waters in south western parts just for a short period at the end of the last glacial period.
You mean – since the ice melted – “where did all of the latent heat come from”.
If the warm waters closer to the tropics don’t mix with the colder water, then they don’t cool down by mixing but by evaporation. The latent heat in the evaporated water is then transported to the polar regions via the atmosphere where it condenses (freezes) and warms the troposphere plus emits LWIR. Mixing distributes the heat and reduces LWIR loss of energy from Earth. Evap distributes the heat to the colder waters but via a mechanism where more is lost to space.
Oops. Misread the units. It was 1800 feet thick, not 1500 metres, so it was 100,000 square miles 1 foot thick melting every year for 1500 years (rounding off the article’s 1800 feet to 1500 to get the one foot per year.) Apologies
There is no Figure 6 in my browser (Firefox).
Interesting discussion Willis. I caught the “self correlated” part fairly early, so proud of myself 🙂
Figure 6 is missing.
Peter
“Setting the details aside, the takeaway message from this graphic is that when the Antarctic coastline gets more ice input from the glaciers, the speed of the circulation increases because more cold water is sinking downwards around the continent.”
Willis, would not the cold water, being fresh, tend to sit atop the salty ocean?
Cheers,
Dave
@Dave,
“Willis, would not the cold water, being fresh, tend to sit atop the salty ocean?”
If I may, actually, no, because that cold water isn’t fresh: it’s saltier than normal. This is due to the higher concentration of dissolved minerals which are forced out by the freezing of sea water. That cold, salty water then sinks & runs along the bottom back towards the tropics, completing the heat loop.
It is true that glaciers deposit large chunks of solid fresh water into the ocean as they calve, but those take time to melt. In so doing, they (generally) restore some of the saline balance to the pole-ward flowing subtropical surface water (which would otherwise have an increased concentration of minerals, thanks to solar evaporation instead of freezing). As such that surface water becomes “fresher” than it otherwise would be, and remains both warmer and less dense/saline than the water which drops to the abyss & flows away from the poles as the sea ice freezes out.
smokey writes
As far as I can see the process Willis is writing about is increased calving at the coastline due to increased snow accumulation in the interior. And when that calved ice melts, it is fresher than the surrounding water because it had the salt forced out but also because it was fresh when it originally fell as snow if you look at the whole of the argument he’s making. Willis then appears to go on to suggest this “colder water” increases circulation but that’s not the accepted norm.
Perhaps I’m misunderstanding your argument. Do you see it differently?
Yet another self regulating thermostat!
ps. I don’t see figure 6?
Willis
As per Dave above, I think the general consensus around melted ice is that it stratifies the ocean rather than increases circulation. That assumption could be wrong…but you’re flying in the face of the commonly accepted mechanism.
Also I’m not quite sure what you’re getting at with the 55W at the coastline equivalent you mentioned. Can you please explain what you mean?
What janked us out of the iceage, it was falling CO2 levels, until a point is reached where vegetation dies off, and countries are turned inot a dust bowl, the dust is blown onto the ice sheets and reduces albedo.
I think the ice cores show the dust layers.
“What janked us out of the iceage, it was falling CO2 levels…”
Could it be that the ice age caused falling CO2 levels? If I recall correctly, cooling starts when CO2 is at a peak levels?
I hold to the theory that the so called last ‘Ice age’ was caused by wandering poles and had nothing to do with global climate change apart from modifying local conditions. The last ‘Ice Age’ ended when the pole migrated over the sea off the North American landmass in the northern hemisphere and onto the Antarctic continental landmass off the sea in the southern hemisphere. Siberia had no glaciation or permanent ice of any kind in the last ‘Ice Age’ and this can only be explained by the north pole migrating in an arc over Europe and North America to its present position.
Colder water holds more CO2. The challenge with climate science IMO is “which came first, the chicken or the egg?” According to Antarctic ice cores changes in temperature occur before changes on CO2 There is lots of “what” but not enough “why.”
“The thing that perplexes me is what it was that abruptly yanked us out of each ice age in one extremely fast period of great warming. But I digress …)”
You do not digress. The default state is clearly warmer. When the das boot of glaciation falters…
It is chilly in antarctica these days and warmer at the North Pole. Is ice accumulating faster up here?
Uncertain, but life isn’t fair. The south pole has been able to sequester continents for all of tectonic history as we know it. The north pole, never.
“The south pole has been able to sequester continents for all of tectonic history as we know it. The north pole, never.”
That’s because the North Pole is at the top and the South Pole is at the bottom. 🙂
Using your numbers for heat – 90 watt-years per cubic metre – 100,000 square miles is roughly 2.6e11 square metres by 0.3 metres thick so 7.8e10 times 90 watts or 7e12 watts per year for 1500 years. The “coast line” would have been longer but using your number of 18e3 for comparison gives 390 watts per metre or 7 times the rate you calculated using ice accumulation alone. Is that correct and if so is it significant? I have no idea.
But thanks for the information.
An excellent post. I was particularly impressed by the fact that the results obtained in fig 4 or 5 were not accepted at face value and the underlying assumptions were sought out and questioned. If I were still teaching environmental science at UEA I would strongly recommend my students to read it as an example of how to do real science.
Please keep this up Willis
Alan Kendall
alan kendall. i think many here would wish you were still teaching environmental science at uea. your successors appear to be failing miserably.
This link on how low CO2 induced stress on high altitude forest and consequent dust impact on ice sheet albedo may have triggered sudden melting of ice caps may be of interest.
https://www.academia.edu/20051643/Modulation_of_Ice_Ages_via_Precession_and_Dust-Albedo_Feedbacks
Pablo
Yes l also think that the sudden increase in dust over the ice sheets is a interesting and important point.
Because what it suggests to me that there was a major shift in wind/weather patterns taking place over the ice sheets during this time. Where l think the paper is wrong is that they think there was a sudden increase in the amount dust in the air. What l think happened is that there was a major change in where this dust was going. Look at a map of the temperature change during the ice age and you will see that the ice age was largely confined to NE North America and NE Europe/NW Russia. This to me has all the hall marks of the set up of a persistent blocking in the weather patterns that was driving cold Polar air down across these areas. What this sudden increase in dust on the ice sheets suggests to me that there was a break down of these weather patterns. And that during this time there was a large increase in warmer air coming up from the south over the ice sheets and a big drop in the flow of cold Polar air. lts this major change in weather patterns aided by this dust is what l think lead to the rapid melting of the ice sheets.
This is no ‘explanation’ since ALL ice ages end the same way and begin the same way and last roughly the same length. Only something that turns this process on and off could cause this. Normally, if one heats up something using flames of some sort, it causes melting, etc. and if one turns off the heat, it cools off to ambient temperatures.
This is why we must first look at a heat source if we wish to know why it gets colder. Namely, our star system called the ‘sun’.
emsnews
lts all very well saying “its the sun” that did it. But unless you explain in detail how the sun affected the earths climate to cause the ice age. Then you are no better off then these who claim that its all down to CO2 levels.
>>Only something that turns this process on and off could cause this.
Not so.
The perennial problem that has plagued palaeoclimatology for decades, is that the response to solar insolation variability is itself variable. Sometimes an insolation maximum causes an interglacial, but many times it does not. That selective response to insolation requires an explanation, and that is what this paper does.
It so happens that successful interglacials always follow dust epochs, lasting about 10,000 years. So it would appear that dust is important in this selective temperature response. But how? Well, this paper give the reason.
R
I agree with this thought. If it gets very cold, plants die and deserts grow. The wind then picks up the dry dirt and vast dust clouds help block the sun. So the acceleration cooling with combo of high ice/snow reflection during calm days and dust cloudsduring windy. A Model for that? Nope.
OT, But
[snip, no buts, that’s what our tips and notes section is for -mod]
……LOL
I’ll offer this thought. The weight of ice over Antarctica is such that it has depressed much of the continent below sea-level (isostasy). The more that accumulates, the greater the depression and, at least for a while, the less gets to the edges and floats away as icebergs.
Why not. One mile of ice sheet presses the continent 300 meters down, which is probably enough to let sea currents calve now grounded shelves. The same should happen in Canada and Northern Europe.
The theory that warmer air holds more water maybe true in the laboratory but history shows that it is the cooler periods that produce the greater number of storms, greater rainfall etc.
Thanks, John. I’ve shown that in the tropics warmer is indeed wetter. See Figure 2 here.
So if you have evidence to the contrary, please link to it.
w.
johnmarshall – more storm, yes. but more rainfall ???
I don’t believe this is true. More heat must put more moisture into the atmosphere. It will fall when it finds cooler air to condense in. This may mean it rains or snows more where it is cooler but that is confusing cause and effect. Where i live it rarely snows when it is below minus 30C. It may clearly be cold enough to condense but there is no moisture in the air.
more warmth => greater snowfall
Willis
Compliments on interesting exploration, especially the ice flow/calving rate.
That brings to mind the advances in quantitative modeling of the ocean:
Marshall, John, and Kevin Speer. Closure of the meridional overturning circulation through Southern Ocean upwelling Nature Geoscience 5, no. 3 (2012): 171-180.
Note 168 citations
e.g., Evidence for link between modelled trends in Antarctic sea ice and underestimated westerly wind changes
Quote:
To do that, I looked at the various methods for dating an ice core. Turns out there are four of them—count the annual rings, align to known events, radioactive dating, and use a “flow model”. Problem is that the first three methods only get us back about 80,000 years into the past.
______________________________
There is another method, which is tuning the ice temperature record to Milankovitch cycles. And just about every ice core record out there has some kind of orbital tuning included in the dating, some more than others. And they also contain the Mont-Berlin ash layer from 92 kyr ago, and the B-M magnetic reversal 778 kyr ago, which are two fairly accurately dated chronological pegs to hang the chronology on. So the beginning and end of the ice age chronology are well known, while the bits in the middle are uncertain.
According to Professor Huybers, when I contacted him, the only ice age chronology that does not contain ‘orbital tuning’ is the sea-silt core record he made, which was deliberately separated from Milankovitch cycles. But in doing so, the vast majority of his record has to depend on silt-depth and flow model ‘guesswork’, much as Willis points out. So instead of having multiple orbital (Milankovitch) date-fixing throughout the core, Huybers ended up with just two fixed points – the age of the Holocene warming and the B-M magnetic reversal 778 kyr ago, which is why his chronology comes back into line with orbitally tuned ice core chronologies at that time.
So the ice core chronologies are pretty accurate, but only if you believe and understand that interglacials and the smaller ‘failed interglacials’ warming events are all orbitally driven – mostly by the precession of the equinox.
The Prof Huybers ocean silt chronology (not orbitally tuned).
https://www.researchgate.net/publication/222422233_Huybers_P_Glacial_variability_over_the_last_two_million_years_An_extended_depth-derived_age_model_continuous_obliquity_pacing_and_the_Pleistocene_progression_Quat_Sci_Rev_26_37-55
Ralph
P.S. Willis – are your figures 4 and 5 reversed?
.
Thanks, Ralph. you say:
Mmm … citation?
w.
Perhaps the best paper on ice core dating is Parrenin et al, The EDC3 chronology for the EPICA Dome C ice core:
http://www.clim-past.net/3/485/2007/cp-3-485-2007.pdf
This pertains to the EPICA core, which is one of the latest drilled, and which has verified much of the chronology work done on the previous cores. But they do quite a lot of comparison work – make of that what you will. The chronology techniques they use include:
2.1 Dated volcanic eruptions during the last millenium
2.2 Synchronisation onto GICC05 with 10Be (6 kyr)
2.3 CH4 during the last deglaciation
2.4 The Laschamp event
2.5 The Mont Berlin ash layer
2.6 Timing of termination II
2.7 Air content age markers 0–440 kyr BP (orbitally tuned)
2.8 18Oatm age markers for stages 300–800 kyr BP (orbitally tuned)
2.9 The Brunhes-Matuyama reversal
Here are some relevant quotes for you:
(Note: Specmap is the most orbitally tuned chronology of all of them…)
Ice flow modelling has been historically used to date ice cores from Greenland and Antarctica. A one-dimensional flow model was first applied to Camp Century (Dansgaard and Johnsen, 1969), and later to GRIP (Johnsen and Dansgaard, 1992; Johnsen et al., 2001). The Camp Century, Dye-3 and GISP2 cores were also interpreted by matching the oxygen 18 isotope record of ice or air bubbles to the SPECMAP stack (Dansgaard et al., 1985; Bender et al., 1994), which is itself orbitally tuned.
The Vostok ice core has also been dated by matching to the orbital SPECMAP scale (Bender et al.,
1994), or directly to insolation variations (Waelbroeck et al., 1995; Shackleton, 2000).
Comparison of paleoclimatic records to insolation variations (so-called orbital tuning methods) are generally applicable to a whole ice core, as long as the stratigraphy is preserved (e.g., Martinson et al., 1987; Dreyfus et al., 2007).
A relationship between the isotopic composition of atmospheric oxygen (18O of O2, noted 18Oatm) and daily northern hemisphere summer insolation has been observed at Vostok for the youngest four climate cycles. This property has been exploited to construct various orbital age scales for Vostok (Petit et al., 1999; Shackleton, 2000). Dreyfus et al. (2007) used a similar approach to derive an age scale for the bottom part of the EDC ice core (300–800 kyr BP) by assuming that 18Oatm lags the summer-solstice precession variations by 5 kyr with an estimated uncertainty of 6 kyr. The selected age markers are placed at each mid-transition of 18Oatm (see Dreyfus et al., 2007, for more details).
Ralph
The close correlation between interglacials (and failed interglacials) and the precessional cycle can be seen in my Fig 2 (reproduced below), which was kindly created by Prof Palmer. However, although the basic profile of the temperature here is ‘accurate’, its precise correlation with each precessional maximum is achieved through ‘orbital tuning’. Otherwise there would be differences of a few thousand years here and there.
However, since the temperature spikes in this record match the precessional cycle very well anyway, and the precessional varies hugely from 15 kyr to 27 kyr, I think they are quite justified in ‘tightening up’ the correlation to make them match perfectly. It makes sense to me.
Orbital data is taken from Laskar 2004:
The Institut de mecanique celeste et de calcul des ephemerides.
http://vo.imcce.fr/insola/earth/online/earth/online/index.php
Graph and explantaions from my paper (which is in peer-review):
https://www.academia.edu/20051643/Modulation_of_Ice_Ages_via_Precession_and_Dust-Albedo_Feedbacks
Temperature vs precessional insolation at 65ºN, courtesy Prof Palmer.
http://s27.postimg.org/b5rt8k4ab/temps_insolation_Page_1.jpg
Just a few thoughts?
What about the Weather?
Is its severity in the polar regions a function of temperature or ice cover or both?
Increased/decreased albedo?
If the severity of storms and winds decreased, would that allow the ice sheets to extend further and reinforce a feedback loop there?
If the severity of storms decreased, would that decrease the mechanical pressures that help calving?
Interesting theory Willis, but I think you have one error.
You say:
This is correct, about 11 watt-years for melting, 72 watt-years for evaporation, and the rest for heating.
However, the cooling effect at the rim of the Antarctic ice shelf would only come from the melting part. The heating and the evaporation needed to create the precipitation occurs on the entire southern hemisphere.
If I am correct here, the cooling per meter of the coastline will therefore be only be 12% of what you have calculated.
/Jan
Thanks, Jan. The true answer is likely in between the two answers. However, remember that the evaporation which is driving the addition of ice to Antarctica happens preferentially around the coastline, which is why I included the evaporative cooling in the calculation.
w.
Well, I would imagine that most of the evaporation happens in the much warmer sea further from the Antarctica than in the ice-cold water close to the ice-shelf.
But I agree that some evaporation will also happen around the coastline, so the truth will likely be somewere between the two answers as you say.
Jan
The Antarctic Katabatic wind suggests that the initial evaporation could occur at any distance from Antarctica?.
Hi Willis
I was thinking about this again, and I realize now that you cannot include the evaporation energy at all because the evaporation and condensation occurs at virtually the same point in time.
That is unlike the freezing and melting which occurs thousands of years apart.
It is therefore only the freezing and melting that causes energy transport over time. Evaporation and condensation causes energy transport between ocean and atmosphere, but it does not play as a mechanism over thousands of years.
Jan
Jan Kjetil Andersen February 26, 2016 at 10:53 pm
Jan, thanks as always for your interesting comments.
The freezing and melting are both going on constantly. So the interval between them is not a factor. What is important is the rate of calving. When that increases, more cold is being transferred from the continent to the coast, and vice versa.
And curiously, despite the freezing and melting occurring thousands of years apart, there is no such lag between increased accumulation and increased calving.
This is because the calving rate depends on the pressure on the cap, and the pressure is transmitted instantaneously from the surface to the base and everywhere. As a result, as soon as the accumulation rate increases, so does the calving rate.
So both the evaporation on the one hand, and the changes in accumulation rate and the resulting changes in calving rate on the other hand, are all going on today, regardless of the interval between freezing and melting.
And as a result, we need to include both the melting and the evaporation in the changes under discussion.
At least that’s how I see it,
w.
I see your point Willis, but I think there are two problems with it.
Firstly, the time from freezing to melting.
Consider two simplified models of a 1000 meter thick shelf where it is 10, 000 years between freezing and melting. Each year the some snow are added on the top, and the same amount are melting/ calving away.
What happens if the precipitation doubles and all other factors are held constant?
One model could be that the calving/melting remained unchanged for the next 9999 years. This would lead to a doubling of the ice volume.
A second model could be that the melting calving immediately doubled from year one because of higher internal pressure. This would give constant ice volume, independent of the precipitation level.
The true answer lies between these two models. The ice shelf would grow in the beginning because the calving/ melting would be unchanged for several years. Then the calving / melting would gradually increase as the internal pressure grew.
I would guess that it the ice shelf would grow considerably before the melting / calving reached the same level as the precipitation.
That means that it has to be a lag, and I would guess that lag to be at last several centuries if not millennia’s.
Then I come to the second problem: I thought that lag was the whole point of the story.
Because if you consider that the second model is the most correct, i.e. that the ice-volume is more or less constant and independent of the precipitation level, then there would be no transport of energy from one time period to another either.
And the theory falls apart, doesn’t it?
True, higher precipitation give higher energy transport between the ocean and the atmosphere, but you do not need to go to Antarctica to find that.
Jan
Quite apart from the rate of evaporation off the surrounding ocean there is also a cycle in the latitudinal insolation gradient. If you look at the relative difference in insolation between 40S and 70S and its impact on atmospheric heating you get a cycle in the meridional temperature gradient. This is what ultimately is what drives much of the change in the position of the southern westerly wind belt. It has a big impact on the delivery of heat and moisture into the Antarctic interior. The pattern closely mimics the temperature fluctuations at Vostok. In other words the changes in the insolatiuon gradient are likely responsible for a large component of the Vostok temperature cycle and the Vostok ice accumultation cycle.
This reduces the extent to which one needs to rely on changes in atmospheric CO2 content to explain the Vostok temperature cycle. Basically the heat is blown in on the wind rather than trapped over Antarctica by CO2. Given that increased CO2 over Antarctica probably actually cools the surface the likelyhood that one can imply much from the CO2 variation over Antarctica was probably always rather low. Note that the Atmospheric CO2 cycle over Antarctica is the primary mechanism used to explain the temperature fluctuation by James Hanson and many others. It is a fundamental cornerstone of the whole IPCC enterprise.
Quote:
As an aside, for me the mystery is not what it was that slowly and gradually pushed us into each ice age with lots of fits and starts. The thing that perplexes me is what it was that abruptly yanked us out of each ice age in one extremely fast period of great warming. But I digress …
_____________________________
My take on this is that the primary forcing agent for interglacial warming is dust.
World temperatures on glacial scales are governed by albedo, not CO2. The preferred state for the climate (over the last million years) is the glacial ice age mode. World temperatures are driven down by increasing ice sheets and therefore increasing albedo, which greatly reduces the net energy absorbed by the Earth, especially during the all-important northern summer. However, there are two elements that can combat the supremacy of ice-sheet albedo and they are: precessional cycles and dust.
Precession can increase the insolation hitting the northern ice sheets by 90 wm2 each summer, during the precessional maximum (which lasts for 5,000 years). Conversely, dust can lower the ice-sheet albedo by a substantial amount. Just 400 ppm of dust on the surface of the ice sheets can lower the albedo by 0.45, and thereby increase the absorption of insolation by another 90 wm2.
The combination of these two elements will give a total increase of 180 wm2. So this is not the paltry 4 wm2 said to result from a doubling of Co2, but a massive 180 wm2, directed regionally and seasonally upon the ice sheets themselves. So just as the normal annual summer melts the snow-pack in the northern hemisphere, precession plus dust can melt the ice age ice sheets. And all interglacials happen to be preceded by massive dust storms, just as the ice record confirms. Note also that most interglacials only last for 5,000 years – the length of a precessional maximum in the northern hemisphere.
And voila, the result of these interactions explains the entire ice age record for the last million years. And Co2 does play a role in all this, but not in a fashion that the Greens would like. Interestingly, Co2 plays the role of the evil stepmother, trying to destroy the world but inadvertently saving the world from becoming an complete snowball.
https://www.academia.edu/20051643/Modulation_of_Ice_Ages_via_Precession_and_Dust-Albedo_Feedbacks
Ralph
Most likely these massive dust storms happened because…the warming ALREADY is beginning but is masked by these dust storms. That is, our atmosphere is warming up first, no? Something is shining in the sky making it warmer all of a sudden.
Actually, the warming dust storms began about 10,000 years before the interglacial warming. See fig 4 in the paper.
ralfellis
l don’t think that dust is the cause of the warming but rather it aided the warming and its because the melting was so quick it what makes me think this.
Why? because l think a large part of the cause of the ice age, was blocking weather pattern bringing cold Polar air down across the areas where the ice sheets were. Now if this was the case as l believe then this air mass would have had low dust content. Because the dust would have to have come from somewhere that was mostly to the south of the ice sheets. So with a Polar air flow over the ice sheets for most of the time. This dust would have to have taken a very indirect route to get onto the ice sheets. As most of the dust would have dropped by the time it got there. But if these blocking weather patterns broke down and this lead to a large increase in winds coming up somewhere from the south. Then this would have lead to a more direct route for the dust to land on the ice sheets. So l believe it was the large increase in a warmer airflow aided by this dust is what lead to the rapid melting of the ice sheets.
Yes, but that descending polar air flowing off the ice sheet is simply one component in a massive ‘sea breeze front’ circulation. If there is a wind flowing off the ice sheets, then it is being replenished by upper air flowing onto the ice sheets at higher levels. And this circulation has been demonstrated in modern Greenland, where that exact flow-pattern has been observed. So the dust can easily get onto the ice sheets, whenever there is dust in the local atmosphere.
ralfrllis
Thanks for the reply. lf that is the case then would it not cast doubt about the idea that the dust is the cause of the rapid warming at the end of the ice age.? As you stated to emsnews that the dust storms started 10,000 years before the rapid warming.
l myself don’t believe that dust was the cause of the end of the ice age.lts just that l understand how it could have been a aid to the rapid warming. Myself l think the main cause of the warming was the shutting down of what was at the time the prevailing northerly winds of the ice sheets areas.
lf that is the case then would it not cast doubt about the idea that the dust is the cause of the rapid warming at the end of the ice age.? As you stated to emsnews that the dust storms started 10,000 years before the rapid warming.
_______________________________
Not so.
As the paper cleary explains, dust (and its albedo reduction) is not powerful enough on its own to create an interglacial – because each dust layer is covered by another year of snow the next year. What is required, is the assistance of increasing insolation during a precessional maximum (a Great Summer), which can increase by 90 wm2.
Only then is there enough insolation and absorption, to begin a melting process. But once the melting starts, the dust from previous years concentrates on the surface of the ice sheets and the albedo falls almost exponentially. And this results in much greater absorption and rapid melting.
It is all explained. Give it a read, and see for youself.
Ralph
This is what ice sheets look like, when dust starts to concentrate on the surface. Note how low the albedo can go, in comparison with pristine snow and ice.
Incidentally, it may well be that the early melt and retreat of Arctic ice in recent years has been caused by Chinese soot and dust, in a very similar fashion. Which would certainly explain the great difference between the Arctic sea ice retreat and the Antarctic sea ice growth. A paper was written a few years ago, explaining that all the Alpine glacial retreat since the 19th century was caused by industrial soot.
http://www-tc.pbs.org/prod-media/newshour/photos/2013/01/30/IMG_4154_slideshow.jpg
Thanks for the interesting post.
Yes l can see how the dust would have help with the melting when the right conditions come along. But am rather more convinced that the reason for the warming was due to the change in the weather patterns over the ice sheets to the sort we have today. Here in europe the ice sheet extended as far as SW Ireland.
When you understand the present climate in Ireland you understand how even during a cooling climate it still would have been a serious challenge to have got the ice sheet to extend over there. Had the weather patterns been of the same type as they are today. Yet that is just what happened, and it was that what started to convince me that reason for the ice sheet growth in europe was largely due to the change in the weather patterns.
Ralfellis,
That picture is worth a thousand words. Where is it from?
Don’t forget algae forms under the ice, and then ice gets broken and flipped, and some “blackened” ice is not due to mankind’s soot or volcanic ash. (Just to add another variable.)
Various polar cameras have pictured some amazingly blackened ice.
Caleb:
It is in Greenland.
I took it from the Dark Snow Project, which is (was) trying to prove that recent ice sheet retreat has been caused by wildfires or industrial pollution. I think they concentrated on wildfires, because they could then cite ‘climate change’ and get funding. But because they mentioned pollution, they did not get any. Typical of the current funding bandwagon, which only rewards conformist believers.
So despite this being a very promising field of climate research, they had no grants, and were trying to fund their expeditions by public crowd-funding. And politicians wonder why scientists have become prostltutes, who will say yes to anything to get grants.
Dark Snow Project.
http://darksnowproject.org
Ralph
Ralph,
A worthwhile project. I hope you can get your results published.
“This means the 0.9 W/m2 across the continent becomes about 0.9 * 618 = 55 watts of heating or cooling per metre of coastline.”
Should that be 556 watts of heating or cooling per metre of coastline?
True dat, good catch. I’ve fixed it.
w.