It is common to find blogs and articles from what we might call the “consensus climate science” corner that we know what caused the ice ages.
The cause being changes in solar insolation at higher latitudes via the orbital changes described in Part Four and Five. These go under the banner of the “Milankovitch theory”.
While that same perspective is present in climate science papers, the case is presented more clearly. Or perhaps I could say, it’s made clear that the case is far from clear. It’s very very muddy.
Here are Smith & Gregory (2012):
It is generally accepted that the timing of glacials is linked to variations in solar insolation that result from the Earth’s orbit around the sun (Hays et al. 1976; Huybers and Wunsch 2005). These solar radiative anomalies must have been amplified by feedback processes within the climate system, including changes in atmospheric greenhouse gas (GHG) concentrations (Archer et al. 2000) and ice-sheet growth (Clark et al. 1999), and whilst hypotheses abound as to the details of these feedbacks, none is without its detractors and we cannot yet claim to know how the Earth system produced the climate we see recorded in numerous proxy records.
[Emphasis added].
Still, there are always outliers in every field and one paper doesn’t demonstrate a consensus on anything. So let’s take a walk through the mud..
Wintertime NH High Latitude Insolation
Kukla (1972):
The link between the Milankovitch mechanism and climate remains unclear. Summer half-year insolation curves for 65°N are usually offered on the assumption that the incoming radiation could directly control the retreat or advance of glaciers, thus controlling the global climate.
The validity of this assumption was questioned long ago by Croll (1875) and Ball (1891). Modern satellite measurements fully justify Croll’s concept of climate formation, with ocean currents playing the basic role in distributing heat and moisture to continents. The simplistic model of Koppen and Wegener must be definitely abandoned..
..The principal cold periods are found, within the accuracy limits of radiometric dating, to be precisely parallelled by intervals of decreasing winter insolation income for Northern Hemisphere (glacial insolation regime) and vice versa. Gross climatic changes originate in winters on the continents of the Northern Hemisphere.
Just for interest for history buffs, he also comments:
Two facts are highly probable: (1) in A. D. 2100 the globe will be cooler than today (Bray 1970), and (2) Man-made warming will hardly be noticeable on global scale at that time.
Self-Oscillations of the Climate System
Broecker & Denton (1990):
Although we are convinced that the Earth’s climate responds to orbital cycles in some fashion, we reject the view of a direct linkage between seasonality and ice-sheet size with consequent changes to climate of distant regions. Such a linkage cannot explain synchronous climate changes of similar severity in both polar hemispheres. Also, it cannot account for the rapidity of the transition from full glacial toward full interglacial conditions. If global climates are driven by changes in seasonality, then another linkage must exist.
We propose that Quaternary glacial cycles were dominated by abrupt reorganizations of the ocean-atmosphere system driven by orbitally induced changes in fresh water transports which impact salt structure in the sea. These reorganizations mark switches between stable modes of operation of the ocean-atmosphere system. Although we think that glacial cycles were driven by orbital change, we see no basis for rejecting the possibility that the mode changes are part of a self-sustained internal oscillation that would operate even in the absence of changes in the Earth’s orbital parameters. If so, as pointed out by Saltzman et al. (1984), orbital cycles can merely modulate and pace a self-oscillating climate system..
..Existing data from the Earth’s glacier system thus imply that the last termination began simultaneously and abruptly in both polar hemispheres, despite the fact that summer insolation signals were out of phase at the latitude of the key glacial records..
..Although variations in the Earth’s orbital geometry are very likely the cause of glacial cycles (Hays et al., 1976; Imbrie et al., 1984), the nature of the link between seasonal insolation and global climate remains a major unanswered question..
[Emphasis added].
Strictly speaking this is a “not quite Milankovitch” theory (and there are other flavors of this theory not covered in this article). I put forward this paper because Wallace S. Broecker is a very influential climate scientist on this topic and the subject of the thermohaline circulation (THC) in past climate, has written many papers, and generally appears to stick with a “Milankovitch” flavor to his theories.
Temperature Gradient between Low & High Latitude
George Kukla, Clement, Cane, Gavin & Zebiak (2002):
Although the link between insolation and climate is commonly thought to be in the high northern latitudes in summer, our results show that the start of the last glaciation in marine isotope stage (MIS) 5d was associated with a change of insolation during the transitional seasons in the low latitudes.
A simplified coupled ocean-atmosphere model shows that changes in the seasonal cycle of insolation could have altered El Nino Southern Oscillation (ENSO) variability so that there were almost twice as many warm ENSO events in the early glacial than in the last interglacial. This indicates that ice buildup in the cooled high latitudes could have been accelerated by a warmed tropical Pacific..
..Since the early 1900s, the link between insolation and climate has been seen in the high latitudes of the Northern Hemisphere where summer insolation varies significantly.
Insolation at the top of the atmosphere (TOA) during the summer solstice at 65°N is commonly taken to represent the solar forcing of changing global climate. This is at odds with the results of Berger et al. (1981), who correlated the varying monthly TOA insolation at different latitudes of both hemispheres with the marine oxygen isotope record of Hays et al. (1976). The highest positive correlation (p ≤ 0.01) was found not for June but for September, and not in the high latitudes but in the three latitudinal bands representing the tropics (25°N, 5°N, and 15°S)..
..At first glance the implications of our results appear to be counterintuitive, indicating that the early buildup of glacier ice was associated not with the cooling, but with a relative warming of tropical oceans. Recent analogs suggest that it might even have been accompanied by a temporary increase of globally averaged annual mean temperature. If correct, the main trigger of glaciations would not be the expansion of snow fields in subpolar belts, but rather the increase in temperature gradient between the low and the high latitudes.
[Emphasis added].
A Puzzle
George Kukla et al (2002) – written along with a cast of eminents like Shackleton, Imbrie, Broecker:
At the end of the last interglacial period, over 100,000 yr ago, the Earth’s environments, similar to those of today, switched into a profoundly colder glacial mode. Glaciers grew, sea level dropped, and deserts expanded. The same transition occurred many times earlier, linked to periodic shifts of the Earth’s orbit around the Sun. The mechanism of this change, the most important puzzle of climatology, remains unsolved.
[Emphasis added].
Gradient in Insolation from Low to High Latitudes
Maureen Raymo & Kerim Nisancioglu (2003):
Based mainly on climate proxy records of the last 0.5 Ma, a general scientific consensus has emerged that variations in summer insolation at high northern latitudes are the dominant influence on climate over tens of thousands of years. The logic behind nearly a century’s worth of thought on this topic is that times of reduced summer insolation could allow some snow and ice to persist from year to year, lasting through the ‘‘meltback’’ season. A slight increase in accumulation from year to year, enhanced by a positive snow-albedo feedback, would eventually lead to full glacial conditions. At the same time, the cool summers are proposed to be accompanied by mild winters which, through the temperature-moisture feedback, would lead to enhanced winter accumulation of snow. Both effects, reduced spring-to-fall snowmelt and greater winter accumulation, seem to provide a logical and physically sound explanation for the waxing and waning of the ice sheets as high-latitude insolation changes.
Then they point out the problems with this hypothesis and move onto their theory:
We propose that the gradient in insolation between high and low latitudes may, through its influence on the poleward flux of moisture which fuels ice sheet growth, play the dominant role in controlling climate from ~3 to 1 million years ago..
And conclude with an important comment:
..Building a model which can reproduce the first-order features of the Earth’s Ice Age history over the Plio-Pleistocene would be an important step forward in the understanding of the dynamic processes that drive global climate change.
In a later article we will look at the results of GCMs in starting and ending ice ages.
Summertime NH High Latitude Insolation
Roe (2006):
The Milankovitch hypothesis is widely held to be one of the cornerstones of climate science. Surprisingly, the hypothesis remains not clearly defined despite an extensive body of research on the link between global ice volume and insolation changes arising from variations in the Earth’s orbit. In this paper, a specific hypothesis is formulated. Basic physical arguments are used to show that, rather than focusing on the absolute global ice volume, it is much more informative to consider the time rate of change of global ice volume.
This simple and dynamically-logical change in perspective is used to show that the available records support a direct, zero-lag, antiphased relationship between the rate of change of global ice volume and summertime insolation in the northern high latitudes.
[Emphasis added]
And with very nice curve fits of his hypothesis.
Length of Southern Hemisphere Summer
Huybers & Denton (2008):
We conclude that the duration of Southern Hemisphere summer is more likely to control Antarctic climate than the intensity of Northern Hemisphere summer with which it (often misleadingly) covaries. In our view, near interhemispheric climate symmetry at the obliquity and precession timescales arises from a northern response to local summer intensity and a southern response to local summer duration.
And with very nice curve fits of their hypothesis.
Warming in Antarctic Changes Atmospheric CO2
Wolff et al (2009):
The change from a glacial to an interglacial climate is paced by variations in Earth’s orbit.
However, the detailed sequence of events that leads to a glacial termination remains controversial. It is particularly unclear whether the northern or southern hemisphere leads the termination. Here we present a hypothesis for the beginning and continuation of glacial terminations, which relies on the observation that the initial stages of terminations are indistinguishable from the warming stage of events in Antarctica known as Antarctic Isotopic Maxima, which occur frequently during glacial periods. Such warmings in Antarctica generally begin to reverse with the onset of a warm Dansgaard–Oeschger event in the northern hemisphere.
However, in the early stages of a termination, Antarctic warming is not followed by any abrupt warming in the north.
We propose that the lack of an Antarctic climate reversal enables southern warming and the associated atmospheric carbon dioxide rise to reach a point at which full deglaciation becomes inevitable. In our view, glacial terminations, in common with other warmings that do not lead to termination, are led from the southern hemisphere, but only specific conditions in the northern hemisphere enable the climate state to complete its shift to interglacial conditions.
[Emphasis added]
A Puzzle
In a paper on radiative forcing during glacial periods and attempts to calculate climate sensitivity, Köhler et al (2010) state:
Natural climate variations during the Pleistocene are still not fully understood. Neither do we know how much the Earth’s annual mean surface temperature changed in detail, nor which processes were responsible for how much of these temperature variations.
Another Perspective
Final comments from the always fascinating Carl Wunsch:
The long-standing question of how the slight Milankovitch forcing could possibly force such an enormous glacial–interglacial change is then answered by concluding that it does not do so..
..The appeal of explaining the glacial/interglacial cycles by way of the Milankovitch forcing is clear: it is a deterministic story..
..Evidence that Milankovitch forcing ‘‘controls’’ the records, in particular the 100 ka glacial/ interglacial, is very thin and somewhat implausible, given that most of the high frequency variability lies elsewhere. These results are not a proof of stochastic control of the Pleistocene glaciations, nor that deterministic elements are not in part a factor. But the stochastic behavior hypothesis should not be set aside arbitrarily—as it has at least as strong a foundation as does that of orbital control. There is a common view in the paleoclimate community that describing a system as ‘‘stochastic’’ is equivalent to ‘‘unexplainable’’.
Nothing could be further from the truth (e.g., Gardiner, 1985): stochastic processes have a rich physics and kinematics which can be described and understood, and even predicted.
Conclusion
This is not an exhaustive list of hypotheses because I have definitely missed some (Wunsch, in another paper, notes there are at least 30 theories).
It’s also possible I have misinterpreted the key point of at least one of the hypotheses above (apologies to any authors of papers if so). Attempting to understand the ice ages, and attempting to survey the ideas of climate science on the ice ages are both daunting tasks.
What should be clear from this small foray into the subject is that there is no “Milankovitch theory”.
There are many theories with a common premise – solar insolation changes via orbital changes “explain” the start and end of ice ages – but then each with a contradictory theory of how this change is effected.
Therefore, a maximum of one of these theories is correct.
And my current perspective – and an obvious one from reading over 50 papers on the causes of the ice ages – is the number of confusingly-named “Milankovitch theories” that are correct is zero.
Articles in the Series
Part One – An introduction
Part Two – Lorenz – one point of view from the exceptional E.N. Lorenz
Part Three – Hays, Imbrie & Shackleton – how everyone got onto the Milankovitch theory
Part Four – Understanding Orbits, Seasons and Stuff – how the wobbles and movements of the earth’s orbit affect incoming solar radiation
Part Five – Obliquity & Precession Changes – and in a bit more detail
Part Seven – GCM I – early work with climate models to try and get “perennial snow cover” at high latitudes to start an ice age around 116,000 years ago
Part Seven and a Half – Mindmap – my mind map at that time, with many of the papers I have been reviewing and categorizing plus key extracts from those papers
Part Eight – GCM II – more recent work from the “noughties” – GCM results plus EMIC (earth models of intermediate complexity) again trying to produce perennial snow cover
Part Nine – GCM III – very recent work from 2012, a full GCM, with reduced spatial resolution and speeding up external forcings by a factors of 10, modeling the last 120 kyrs
Part Ten – GCM IV – very recent work from 2012, a high resolution GCM called CCSM4, producing glacial inception at 115 kyrs
Pop Quiz: End of An Ice Age – a chance for people to test their ideas about whether solar insolation is the factor that ended the last ice age
Eleven – End of the Last Ice age – latest data showing relationship between Southern Hemisphere temperatures, global temperatures and CO2
Twelve – GCM V – Ice Age Termination – very recent work from He et al 2013, using a high resolution GCM (CCSM3) to analyze the end of the last ice age and the complex link between Antarctic and Greenland
Thirteen – Terminator II – looking at the date of Termination II, the end of the penultimate ice age – and implications for the cause of Termination II
Fourteen – Concepts & HD Data – getting a conceptual feel for the impacts of obliquity and precession, and some ice age datasets in high resolution
Fifteen – Roe vs Huybers – reviewing In Defence of Milankovitch, by Gerard Roe
Sixteen – Roe vs Huybers II – remapping a deep ocean core dataset and updating the previous article
Seventeen – Proxies under Water I – explaining the isotopic proxies and what they actually measure
Eighteen – “Probably Nonlinearity” of Unknown Origin – what is believed and what is put forward as evidence for the theory that ice age terminations were caused by orbital changes
Nineteen – Ice Sheet Models I – looking at the state of ice sheet models
References
Hopefully in the order they appeared in the article:
The last glacial cycle: transient simulations with an AOGCM, Robin Smith & Jonathan Gregory, Climate Dynamics (2012)
Insolation and Glacials, George Kukla (1972)
The role of ocean-atmosphere reorganizations in glacial cycles, Wallace Broecker & George Denton, Quaternary Science Reviews (1990)
Last Interglacial and Early Glacial ENSO, George Kukla, Clement, Cane, Gavin & Zebiak (2002)
Last Interglacial Climates, George Kukla et al, Quaternary Research (2002)
The 41 kyr world: Milankovitch’s other unsolved mystery, Maureen Raymo & Kerim Nisancioglu, Paleoceanography (2003)
In defense of Milankovitch, Gerard Roe, Geophysical Research Letters (2006)
Antarctic temperature at orbital timescales controlled by local summer duration, Huybers & Denton, Nature Geoscience (2008)
Glacial terminations as southern warmings without northern control, E. W. Wolff, H. Fischer & R. Röthlisberger, Nature Geoscience (2009)
What caused Earth’s temperature variations during the last 800,000 years? Data-based evidence on radiative forcing and constraints on climate sensitivity, Peter Köhler, Bintanja, Fischer, Joos, Knutti, Lohmann, & Masson-Delmotte, Quaternary Science Reviews (2010)
Quantitative estimate of the Milankovitch-forced contribution to observed Quaternary climate change, Carl Wunsch, Quaternary Science Reviews (2004)
You have done a great job summarising the current lack of understanding of the origin of ice ages
The exact cause and evolution of ice ages still remain a mystery. Why did the Earth shift into an unstable climate with global oscillations of 4-5 degreesC every 100,000 years? Proposed Milankowitz cycles cannot properly explain why their relatively small radiative effects apparently have been amplified during the last million years or why long term temperatures have been falling for over 20 million years.
Currently the Earth’s ellipticity is 0.0167 and summer in the Southern Hemisphere coincides with the closest distance to the sun. This also means that winters in the Northern hemisphere are less severe now than they were at the last glacial maximum 13,000 years ago due to the precession of the equinoxes.
Rho’s proposal that rate of change of ice is proportional to 65N insolation looks appealing but it doesn’t really explain at all wyy 100,000 year interglacial periods have prevailed for the last 600,000 years.
Some geological proposal I know of include:
– closing of the Panama canal 3 million years ago cutting circulation between the Atlantic and Pacific resulting in the gulf stream.
– Shifting of Antarctica over the south pole 5 million years ago
– Far slower long term cooling due to uplifting of Tibet plateau leading to glaciations beginning 5 million years ago.
I think that chaotic would be a better term than stochastic. Chaotic systems can couple with relatively small forcings to produce oscillatory behavior. In fact, chaotic systems can exhibit oscillatory behavior with no external forcing. Koutsoyiannis has written extensively on this. In statistical analysis, the time series would exhibit fractionally integrated behavior (ARFIMA(p,d,q) with d ≤ 0.5.
There’s a paper out there somewhere that proposes that NH glaciation is mainly associated with North America because of its geography. Northern Asia gets warmer in the summer because it’s a contiguous land mass so snow is less likely to persist.
While failing to find that paper, I did find this recently published paper: Insolation-driven 100,000-year glacial cycles and hysteresis of ice-sheet volume
Glaciations follow the three Milankovitch cycles even though the net yearly solar radiation reaching the Earth is the same. This is because of the way continents are distributed about the globe: most of the land surface is in one of the hemispheres, the Northern Hemisphere. The 3 cycles interact with each other and at the point in the composite cycle when Northern Hemisphere summers are coolest and winters are warmest, ice can accumulate over land as more snow is left each summer. Ice won’t accumulate over ocean to the same extent. Also, feedback is introduced, by more ice reflecting more of the Sun’s radiation lowering global temperatures. Another possible minor feedback is more land surface area appearing as the oceans levels fall producing more ice. The process reverses when the winters start to get colder and the summers get warmer.
Continents shift over time through Plate Tectonics; hence the effects of Milankovitch cycles will change over the age of the Earth as land masses are redistributed.
Also, according as the Sun rotates about the centre of the Milky Way, through dense star clusters, the intensity of cosmic rays goes up leading to more cloud cover, hence lower temperatures which could trigger an ice age, aided or abetted by the Milankovitch cycles.
As data in the ice cores show, CO2 concentration follows temperature change by about 800 years.
Since the mean global temperature must depend on the balance between incoming and outgoing radiation, we often assume that temperature responds to forcing according to dT = lamba*dF. Even if the functional relationship is more complicated, there is nothing grossly wrong with using a linear approximation for small changes. Unfortunately, the chaotic behavior of climate (and more fundamentally the equations that control heat flow through fluids) should remind us that the relationship does not need to be a mathematic function – a single T for every F. MIT has established a new Lorentz Center to step back and address fundamental questions about climate. The first of four “big questions” proposed by Emanuel and Rothman for this institute was:
“Are two or more statistically stable climate states possible for the same climate forcing (solar radiation, atmospheric composition, configuration of continents)? This is a problem of great inherent intellectual interest and potentially enormous practical consequences as well. At present, we do not know whether the real climate has multiple equilibrium states.”
If multiple equilibrium states (interglacial and glacial) are possible or such states separated by a small difference, “unreasonably small” orbital forcing could trigger transitions. Some chaotic systems exhibit oscillations whose periods can double, potentially resonating with either 41 or 100 kya orbital periods. It is possible our climate crossed a threshold about 2 million years ago (from the gradual burying of CO2 underground? shifting continents? water tied up in Antarctic ice sheet?) where both stable glacial and interglacial states became viable with the current global forcing. Under these circumstances, attempts to calculate a climate sensitivity (lamba) relevant to future warming from forcing and temperature at the LGM wouldn’t make sense, even though lamba might still be relevant to future warming.
Click to access Lorenz_Proposal.pdf
Sorry, but there can ALWAYS be a theory. Its whether or not it holds any merit. And as you quite rightly point out, if any evidence can refute the theory, it has to be rejected.
Just as catalstrophic man-made CO2 induced global warming (CAGW) needs to be put in the rubbish. Its a theory – and a failed one at that.
macha,
In this blog we attempt to stay on a topic and the topic here is ice ages and their causes – so no soap boxes on completely different theories please. If every visitor listed the unrelated theories they didn’t agree with it would clog up the comments.
Occasionally this does happen and it usually fails to create a stimulating environment for everyone.
Plenty of better blogs for soapboxes – with wider audiences.
Part of the feedback of glaciation is the accumulation at higher altitudes of the snow pack itself. Greenland ice persists even though neighboring islands are ice free in summer. This is because the ice sheet elevation of Greenland is high enough that temperatures remain below freezing most summers.
Some summers are hotter or sunnier than others, some are cooler or cloudier than others. When a string of cooler summers occurs, marginal amounts of snow may continually accumulate until a threshold is crossed in which the elevation of the ice becomes self protective.
This explains the stochastic resonance of orbital induced galciation.
LGM: http://en.wikipedia.org/wiki/File:Iceage_north-intergl_glac_hg.png
Now: http://www.triplespark.net/render/img/earth/earth-northpole-aa0.3.jpg
Is roughly 2-3000 m (roughly 13-20 degC colder than sea level) the only reason that the Greenland ice sheet is the only significant remanent of the last ice age?
Yes ice builds up preferentially over the land surface because it’s at higher elevation and the air temperature is colder, simple. Lots of the land is above 45 degrees north and at high elevation so glaciers form. If most of the land were shifted into the tropics then there would be no major ice ages.
From Nir Shaviv http://www.sciencebits.com/CosmicRaysClimate
“Cosmic Rays, at least at energies lower than 1015eV, are accelerated by supernova remnants. In our galaxy, most supernovae are the result of the death of massive stars. In spiral galaxies like our own, most of the star formation takes place in the spiral arms. These are waves which revolve around the galaxy at a speed different than the stars. Each time the wave passes (or is passed through), interstellar gas is shocked and forms new stars. Massive stars that end their lives with a supernova explosion, live a relatively short life of at most 30 million years, thus, they die not far form the spiral arms where they were born. As a consequence, most cosmic rays are accelerated in the vicinity of spiral arms. The solar system, however, has a much longer life span such that it periodically crosses the spiral arms of the Milky Way. Each time it does so, it should witness an elevated level of cosmic rays. In fact, the cosmic ray flux variations arising from our galactic journey are ten times larger than the cosmic ray flux variations due to solar activity modulations, at the energies responsible for the tropospheric ionization (of order 10 GeV). If the latter is responsible for a 1°K effect, spiral arm passages should be responsible for a 10°K effect—more than enough to change the state of earth from a hothouse, with temperate climates extending to the polar regions, to an icehouse, with ice-caps on its poles, as Earth is today. In fact, it is expected to be the most dominant climate driver on the 108 to 109 yr time scale.”
So we have 4 major effects on glaciation: Milankovitch cycles, plate tectonics ,cosmic ray intensity because of passage through the spiral arms and solar modulation of cosmic rays. CO2 comes a poor 5th and is an effect , not a cause.
Hi SoD,
Glad to see you back and as always a fascinating insight into the topic. Clearly the exact mechanism of why we appear to get interglacials every 100k (and lasting about 10k) is not currently known and my never be in my lifetime at least. However, the main relevance for these studies is the impact humans are having on the planet due to our consumption of fossil fuels to power our society. In particular what can this data tell us about the so-called “climate sensitivity”. I believe that the “competing” theories are “C02” or “Ice Albedo” (due to changes in ice sheets). Whilst we are unable to infer the precise mechanisms as you have so elegantly demonstrated, I believe that strong inferences are possible from the data with respect to this.
For me rightly or wrongly the starting point will always be what data I am trying to analysis and in particular how “accurate” or robust this is? Not much point in attempting to analyse intricacies in the “data” were the “detail” are mere artefacts of the particular measuring system. I have to admit that I have not delved into this in any depth but I have a strong suspicious that these estimates of past temperature etc. are merely that and are prone to far high uncertainty which would make detailed analysis meaningfull – effectively trying to analyse noise!
That being said there is many lines of evidence that suggest that the ice ages are fact and give us knowledge of their extent. What I see (again rightly or wrongly) is for the most part of the last XXXk years the world has been dominated by large ice sheets in the Northern hemisphere stretching to some 45 deg N. Occasionally and very briefly (in historical context) these sheets disappear before re-appearing again. In this context the aspects which most puzzle me are the following:-
1) Why do the sheets appear to “Stop” at 45 deg N?
2) Why does the temp stop rising at the peak interglacial?
3) What is the significance of the fact that this is a Northern hemisphere issue?
Based on the above I would be looking to understand whether “CO2” or “Ice Albedo” was the likely cause or not? Since the physics of “Ice Albedo” are relatively simply I would begin by calculating this effect and see what this could explain. To me this has the same merit as the radiative properties of CO2 (settle science – as much as that can ever be)? Once we determine what these affects are what is left is what needs to be explained by other mechanisms. From this we should be able to get a far indication of climate sensitivity?
And another hypothesis, a variant of “Summertime NH High Latitude Insolation”.
Ice Age Terminations, Hai Cheng et al (including Wallace Broecker), Science, 2009
Of course it’s not at all clear that density is that significant a driver of the MOC compared to wind driven currents.
[…] « Ghosts of Climates Past – Part Six – “Hypotheses Abound” […]
[…] Using simple energy balance models to demonstrate there was some physics behind the plausible ideas (we saw a subset of the plausible ideas in Part Six – Hypotheses Abound) […]
[…] graph of insolation at 65ºN on July 1st summarizes the problem for the”classic version” (see Part Six – “Hypotheses Abound”) of the “Milankovitch theory” – in simple terms, if solar insolation at 18 kyrs ago caused […]
[…] Part Six – “Hypotheses Abound” – lots of different theories that confusingly go by the same name […]
I think everything said made a great deal of sense.
However, what about this? suppose you wrote a catchier post title?
I ain’t suggesting your content isn’t good, however suppose you added something to possibly get people’s attention? I mean Ghosts
of Climates Past – Part Six – Hypotheses Abound
| The Science of Doom is a little vanilla. You ought to look at Yahoo’s home page and see how they create article titles to grab people to
click. You might add a related video or a related pic or two to get readers excited about everything’ve
got to say. In my opinion, it might bring your blog a little
bit more interesting.