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Are we heading into a new Ice Age?

What the science says...

Select a level... Basic Intermediate

Worry about global warming impacts in the next 100 years, not an ice age in over 10,000 years.

Climate Myth...

We're heading into an ice age

"One day you'll wake up - or you won't wake up, rather - buried beneath nine stories of snow. It's all part of a dependable, predictable cycle, a natural cycle that returns like clockwork every 11,500 years.  And since the last ice age ended almost exactly 11,500 years ago…" (Ice Age Now)

According to ice cores from Antarctica, the past 400,000 years have been dominated by glacials, also known as ice ages, that last about 100,000. These glacials have been punctuated by interglacials, short warm periods which typically last 11,500 years. Figure 1 below shows how temperatures in Antarctica changed over this period. Because our current interglacial (the Holocene) has already lasted approximately 12,000 years, it has led some to claim that a new ice age is imminent. Is this a valid claim?

Figure 1: Temperature change at Vostok, Antarctica (Petit 2000). The timing of warmer interglacials is highlighted in green; our current interglacial, the Holocene, is the one on the far right of the graph.

To answer this question, it is necessary to understand what has caused the shifts between ice ages and interglacials during this period. The cycle appears to be a response to changes in the Earth’s orbit and tilt, which affect the amount of summer sunlight reaching the northern hemisphere. When this amount declines, the rate of summer melt declines and the ice sheets begin to grow. In turn, this increases the amount of sunlight reflected back into space, increasing (or amplifying) the cooling trend. Eventually a new ice age emerges and lasts for about 100,000 years.

So what are today’s conditions like? Changes in both the orbit and tilt of the Earth do indeed indicate that the Earth should be cooling. However, two reasons explain why an ice age is unlikely:

  1. These two factors, orbit and tilt, are weak and are not acting within the same timescale – they are out of phase by about 10,000 years. This means that their combined effect would probably be too weak to trigger an ice age. You have to go back 430,000 years to find an interglacial with similar conditions, and this interglacial lasted about 30,000 years.
  2. The warming effect from CO2 and other greenhouse gases is greater than the cooling effect expected from natural factors. Without human interference, the Earth’s orbit and tilt, a slight decline in solar output since the 1950s and volcanic activity would have led to global cooling. Yet global temperatures are definitely on the rise.

It can therefore be concluded that with CO2 concentrations set to continue to rise, a return to ice age conditions seems very unlikely. Instead, temperatures are increasing and this increase may come at a considerable cost with few or no benefits.

Basic rebuttal written by Anne-Marie Blackburn


Update August 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

 

Last updated on 7 August 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

Tamino discusses predictions of future solar activity in Solar Cycle 24.

Acknowledgements

Many thanks to Sami Solanki for his invaluable advice and feedback as well as John Cross for his very helpful comments.

Further viewing

potholer54 published a video tackling this myth on June 27, 2020

 

Dave Borlace explains why we are not headed towards an ice age in this "Just have a think" video published in December 2019:

 

Comments

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Comments 376 to 400 out of 410:

  1. I remember as an undergrad in the 1970s that an open Artic Ocean was thought to be one possible way of creating enough precipitation to initiate the growth of continental ice sheets - i.e. initiate a glacial period.

    I also remember that the 1970s was a period where much of the knowledge of glacial geology in Canada's Arctic was being re-written. Flynn's (?) massive single Laurentide Ice Sheet idea was losing to the idea of several ice domes and much more complex movements. (I was a lowly field assistant working in Canada's Keewatin District, on the west side of Hudson's Bay, on research that helped definitively establish the Keewatin Ice Divide as a long-standing feature, not the late glacial feature that it had been claimed to be.)

    So, the idea that moisture from the Arctic Ocean could lead to glacial periods was a serious idea at the time. Knowledge of the systems and causes are much greater now.

  2. Wow!  Thanks for all the feedback everyone.  You are so kind.  I will review all this new data and if I have any further questions I'll jump back in.  This is a real learning experience for me.  Thanks again.  

    Looks like we're in for warmer weather.  We live at about 300' altitude in New Hampshire.  I've told our daugher to hold onto the property as it will likely become beachfront generations down the road.

  3. Wouldnt get your hopes up. You can get 70m (230') by melting all the ice, but melting all of EAIS and GIS would take 1000s of years.

    However even 1m of sea level rise would displace a couple hundred million people who are not so fortunate in their location.

  4. Yes, I was joking on that point and understood on the 1000s of years time required to melt all the ice.  

    But, don't all these forecasts assume some type of elevated CO2 presence for years to come?  I understand that even the most hopeful time scale for full conversion from fossil fuels to renewables with or without the nuclear option is still estimated to be many years away, but I do believe this will happen, and sooner than many people predict today.  As that happens, and as we figure in the relatively rapid natural sequestration of our currently elevated atmospheric CO2 levels (half life in the order of only 20-30 years), I still wonder what the models will show when ocean temperatures have been elevated through all the current (and perhaps for another 50-100 years into the future) CO2 emissions to rather suddenly find their warmed surfaces evaporating into crystal clear skies that can quickly radiate all that heat (but not the moisture) into space.  It will be a unique set of conditions not often seen on the planet.

  5. As a second comment I was intrigued by scaddenp's first link in the discussion above, a link to John Mason's 2013 post regarding past geologic records of 400ppm CO2 found in Russia's Lake E, referred to as a super-interglacial, and ending with the query, is this what we are headed for?  Likely, the answer is yes, but as I mentioned above there should be a caveat that those Pliocene-Pleistocene Series precursors to our current situation had to have had both non-anthropormorphic entrances to and exits from their warm periods.  If the earlier entrance to the 400ppm plus CO2 atmosphere happened as relatively quickly as ours has, then that past cycle might mimic ours.  Does anyone reading this know if the record shows that the CO2 level changed that rapidly, perhaps as the result of some extraterrestrial fireball such as created Lake E and may have burned up all flora on the planet within several years or less?  My apologies for being so uninformed in these things.  But, I am so curious.

  6. DaveMartsolf, concerning CO2 residence time, warming potential can last centuries.

     

    It is true that an individual molecule of CO2 has a short residence time in the atmosphere. However, in most cases when a molecule of CO2 leaves the atmosphere it is simply swapping places with one in the ocean. Thus, the warming potential of CO2 has very little to do with the residence time of CO2.

     

    CO2 emissions change our atmosphere for centuries

  7. Dave Martsolf @379, carbon cycle models have shown that a significant portion of the excess CO2 in the atmosphere will be retained for many thousands of years.  This has been illustrated, along with the relevent processes for drawing down CO2, by David Archer:

    The important thing here, however, is not so much the retained fraction as the rate at which CO2 is drawn down, which approximately matches the rate at which temperatures approach equilibrium with a constant CO2 concentration.  The approximate match of the rates means that with zero emissions, temperatures remain approximately constant:

    That means that if we were to eliminate all CO2 (and other greenhouse) emissions over night, we could expect an equilibrium temperature of 1 C above the preindustrial.  If we allow cumulative emissions 1000 GtC before ceasing all emissions, we could expect an equilibrium temperature of 2 C.  On current policy settings, the stable temperature will be at least 3 C, if achieved at all (it only requires 5-10% of current emissions to result in a constant, or even slightly rising concentration, and no policy pursued by any government currently pursues zero emissions).

    Those estimates hide a host of details.  For instance, while GMST will be approximately constant with zero emissions, ocean temperatures will continue to rise for a short period, while land temperatures fall slightly.  Sea level will continue to rise, both because of the rising ocean temperatures and because the ice sheets will melt back in the face of the constant elevated temperatures. 

  8. "should be a caveat that those Pliocene-Pleistocene Series precursors to our current situation had to have had both non-anthropormorphic entrances to and exits from their warm periods."

    I am not quite sure I follow you, especially with regard to entrance/exit of warm periods. In very broad terms, CO2 has been falling right through the Cenozoic, with exception of PETM. In transition from Pliocene to Pleistocene, CO2 (and surface irradiation) had fallen to level where Milankovich cycles could drive an ice-age cycle. Prior to then, climate was too warm (and CO2 too high). Noone is disputing that orbital forcings drive the Pleistocene ice ages, though turning variations in albedo at 65N into a global event involves several feedbacks of which CO2/CH4 feedbacks are very important. These are hardly analogues of current situation. The pace of change for a start is orders of magnitude faster. If we keep warming, we will also get carbon cycle feedback enhancing the warming but not for 100s of years.

    Perhaps time to look at "Climate has changed before" article as well? Or have I completely misunderstood you?

  9. Deep thank yous to Yail Bloor, Tom Curtis, and scaddenp.  Together you have cleared up all my questions regarding the interrelated processes that are bringing out an unfortunate future to our planet.  I totally understand now why current and near future increased levels of CO2 will be around for centuries.  And, scaddenp's link to Howard Lee's article describing an outcome of rapid CO2 increase that I did not think possible.  I can understand why these facts have not been made into a movie, although they should be.  I want to thank all of you for opening my eyes and for filling in all the blanks in my understanding.  May our future generations find a way to survive The Once and Future Planet.

  10. Interglacials begin to end, generally, as soon as they reach their peaks.  The slide into a glacial is much more gradual that the exit from a glacial As the snow can only accumulate as fast as precipitation exceeds melting of the snow deposited.  Of interest is that the amount of warming we have observed is not the amount we have caused.  To estimate how much we have caused we have to look at what the temperature would likely be at present without the influence of man.  Apparently the interglacial with the Milankovitch cycle most similar to the present one is the interglacial which occured some 400,000 years ago.  On this basis we are up to and probably over 2 degrees C.  Using this point of view, the sensitivity for doubling Carbon dioxide increases a little since the anthropogenic heating per increas of Carbon dioxide is a little more than if we use the actual increase.

  11. Stepping back a bit ... perhaps guessing the precise combinations required to affect the planet's next temperature change is more philosophical than intrically scientific. Have a look at the graph again. Could we all agree that the temperature has fluctuated over time and more or less the colder than we are now parts of the graph take up about 90% of the graph? On the very first graph the times between the hotspot peaks is about 90,000 years, 82,000 years, 108,000 years and until now, 130,000 years. This time the top of the peak has been sawed of and it has lasted somewhat longer than the others ... and 130,000 years is significantly longer than the other integers so no matter what the reasons, I'd say that it's way more likely to get colder than warmer relative to the cycles indicated on the graph. 

    The sawed off peak is not as high as the last three so there appears that the cycle could get warmer yet ... humans in or humans out of the equation. It could even be interpreted that humans have been somehow been keeping the temperature down. Overall, we should be learning how to survive underground, to create food with much less heat ... there is no way that it won't be getting colder soon ... geologically speaking.

    One last thing: why are humans so arrogant as to believe that they have any control of this process?

    Response:

    [JH] Sloganeering snipped. 

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  12. "perhaps guessing the precise combinations required to affect the planet's next temperature change is more philosophical than intrically scientific"

    No guesswork needed.  The Earth's climate doesn't change significantly without a change in factors capable of forcing it to change. When climate is in balance, seasons come and go at their usual times and polar ice cover stays within range of natural variations. As do ocean pH and global temps. If global temps and ocean pH are changing, which we can measure and verify that they are, then there must be a change in the composition of those gross factors which can affect climate.

    The gross factors affecting climate are: Milankovitch cycles (orbital factors), solar output, volcanoes (typically a negative forcing), aerosols, surface albedo and non-condensable greenhouse gases (water vapor plays the role of feedback). Orbital forcing has been negative for the past 5,000 years (since the end of the Holocene Climate Optimum), solar output during the past 40+ years has been flat/negative, volcanoes exert a short-term (up to several years) negative forcing (but none of note since Pinatubo), aerosols (natural and manmade) are a net negative forcing over that time period. Albedo is a net positive forcing due to the ongoing loss of Arctic sea ice; cloud albedo effects are thought to be in general a net zero forcing.

    Radiative Forcing
    Bigger image

    Which leaves the non-condensable greenhouse gases, primary of which are carbon dioxide (CO2) and methane (CH4). Atmospheric levels of both are rising, and have been for literally centuries now, so they are a net warming. While the concentration of CH4 is rising, and it is a potent GHG, the warming from it is overall less than that of CO2 due to the much more massive injection of previously-sequestered, fossil-fuel-derived bolus of CO2 humans are re-introducing back into the carbon cycle.

    "I'd say that it's way more likely to get colder than warmer relative to the cycles indicated on the graph"

    Still no guesswork neded.  Scientists have researched that very subject. What they've found is that the next ice age has been postponed indefinitely.

    Per Tzedakis et al 2012,

    "glacial inception would require CO2 concentrations below preindustrial levels of 280 ppmv"

    For reference, we are at about 400 right now and climbing, so we can be relatively sure the next glacial epoch won't be happening in our lifetimes.

    But what about further down the road? What happens then? Per Dr Toby Tyrrell (Tyrrell 2007) of the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton:

    "Our research shows why atmospheric CO2 will not return to pre-industrial levels after we stop burning fossil fuels. It shows that it if we use up all known fossil fuels it doesn't matter at what rate we burn them.

    The result would be the same if we burned them at present rates or at more moderate rates; we would still get the same eventual ice-age-prevention result."

    and

    "Burning all recoverable fossil fuels could lead to avoidance of the next five ice ages."

    So no ice ages and no Arctic sea ice recovery the next million years...

    Also covered by Stoat, here

    This Nature article offers an interesting summary

    Paper listing on the topic

    Ganopolski et al 2016 - Critical insolation–CO2 relation for diagnosing past and future glacial inception

    GHG emissions have canceled the next ice age summary.

    Another such summary

  13. Shorter Daniel:

    Because we know science, and understand physics, we know that human activities are the cause of the current warming, and the warming will continue, for decades-to-centuries after the cessation of the burning of fossil fuels.

  14. "Ice ages take thousands of years to develop. If you're that concerned about an impending ice age, just look to northern Canada. If there's a giant ice sheet slowly creeping down the North American continent, then you have reason to be concerned. But if glaciers are retreating worldwide and the Greenland and Antarctic ice sheets are losing ice mass at an accelerating rate, you can relax about the possibility of an upcoming ice age in your lifetime and the lifetime of your children and grandchildren."

    Glaciers don't creep per se. If The world entered into an ice age it would start as a few decades of cold climates and entire summers where the snow never melts. The first decade it would be a few tens of feet of snow, then a few hundred. Then a few feet of ice. 30 years of cold climates mean the snow and ice never leave. Within 50 years a couple of miles thick is doable, depending on precipitation.

    Glaciers grow from the heavens and creep along hell.

    Response:

    [PS] This is at odds with every paper I have read. Please cite references to support your assertions or your comment will be removed for sloganeering  (see the comments policy). I should add that this also contradicts ice core dating and basic physics (viz to get thick snow fall you need a lot water vapour in the air which needs warm temperatures. Antarctica is one of driest places on earth).

  15. In relation to comment #70 of Dave Martsolf re Betty Friedon on  the open arctic ocean.  This is probably part of it.  In 1960 two geologists (I am still searching for the paper) suggested a lake effect off the arctic ocean as the cause of the ice age.  I have never had a reason to doubt this.  There were some minor objections regarding water temperature, so the theory has been pretty much neglected since then. The actual cause of the ice age is due to the influx of water through the Bering Strait,  gradually undermining the ice cover.  When enough of the ocean is open and the temperature is right the lake effect dumps enormous amounts of snow over northern Canada.  My guess is around three feet a day for about six months or about 540 feet per season.  Most of this consolidates as ice.  I majored in geology and have worked in astronomy.  The various astronomical cycles may influence the exact shape of the temperature and CO2 curves, but they do not cause it.  Global warming due to human intervention may accelerate, but does, not cause the ice age.  The massive deposits of snow drop the arctic sea level so much that massive amounts of water are drawn in from the Atlantic and the Pacific.  As the moisture is drawn off it leaves the salt behind, dropping the freezing point ever lower, making it increasingly difficult for the ocean to freeze over and stop the flow.  Eventually, the flow from the Pacific is cut off as the sea level drops so low that it exposes the Bering land bridge.  Since the lake effect continues, it accelerates the flow from the Atlantic .  Eventually the Arctic Ocean starts to freeze from the Bering Strait until it refreezes to the east and the ice age ends.  Then the ice melts very quickly as the temperature rapidly rises, and the cycle starts all over again.  However, it takes many thousands of years before the arctic opens again.  At first, I thought we had another 5000 years to go;   then 500. And now it look like it could be 50.  Indeed, we may have only a few years, if in fact it has not already begun.    Again, global warming may accelerate the time of onset, but it does not cause it.  The cause is not astronomical, but hydrological. The drop in sea level will quickly become evident.  The decline in temperature and CO2 will be slow, with CO2 falling eventually to about 175 ppm, and temperature (at least in the northern hemisphere) dropping as much as 14 degrees F.  There is nothing that can be done to prevent this from happening.  In the end, sea level might fall as much as 650 feet.  Even before the ice gets this far south the building ice dome will cause frigid temperatures as the air pours off of it.  At its maximum extent, Canada will be almost entirely covered, as well as the northeast from St Louis along the Ohio River to Long Island.  The southwest will be cooler and wetter, as will southern Europe.  The Sahara will be like the Serengeti.  Any place bordering on the ocean will find their coastlines greatly extended.  Most of the Adriatic will be land.

    Response:

    [JH] Because you have not provided appropriate documentation to support your extraordinary claims about how and why the climate system changes, your comment is sloganeering and has been snipped. Sloganeering is prohibiited by the SkS Comments Policy

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  16. Correction:  The Martsolf comment is #370.

  17. In regards to the "what would happen if the sun went through another Maunder Minimum?" question.

     Maunder minimum,is an unexplained period of drastically reduced sunspot activity, this has previously occurred between 1645 and 1715. In theory we know that the warmth of the sun can affect the earth. Thus a lack of sun could lead to decreased glacial melting and allow glacial production to increase and push outwards.

    Response:

    [TD] A Maunder Minimum type event would merely slow down warming a little bit for one or two decades. Type “Maunder” into the search field at the top left of this page.

  18. Even a prolonged Maunder Minimum / Grand Solar Minimum would only serve to offset a few years of warming caused by human activities.

    The change in solar forcing is about -0.1W/m2, which would be made up in just 3 years of current CO2 concentration growth:

    https://www.nature.com/articles/ncomms8535
    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014JD022022
    https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2013EF000205
    https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028922

     

    Grand Solar Minimum

  19. I was sure cherry picking was involved.  I searched Tamino's site before posting here but didn't come acoss the article you posted.  My search skills need improvement.  

  20. This answer is not adequate, and this is the one aspect of climate change that I can't get past. You are not using enough hard scientific facts to support your position.

    Firstly, you say there was a similar condition as ours over 400,000 years ago that had a warming period of 30,000 years, but it is an N of 1. How can we rely on just one instance of data? I feel like this singular piece of data cannot be used as support for this argument.

    Secondly, there is no hard data offered in this argument to show why the tilt and orbit are weak for this time period. When you are talking about thousands of years, the timing may be off by a couple decades. Just because you don't see things happening don't mean that they will not happen. This is a common falacy people have. Possibly the scientific community is measuring the wrong things? We should be looking at leading indicators of ice age activity.

    Thirdly, there is also no discussion about the benfits of C02 which if it is stalling an ice age has likely helped save billions of lives as a new ice age would be catastrophic. Possibly there is a necessity for some C02 emission to prevent an ice age from forming.

  21. AlexDeBastiat @395 ,

    Of the glaciation/deglaciation cycles of the last million years, each cycle has been unique in structure, because the precise relations of orbital eccentricity and planetary tilt have been subtly different.

    So every cycle has been an "N of 1" .   Yet the paleo evidence shows that these climate variations have nevertheless operated within narrow limits of conformation.  And from those past cases we know that the present Interglacial would "naturally" last something upwards of 25,000 years without the human intervention which has now occurred.  ( It is perhaps rather too early to say whether the current high levels of CO2 will cause a complete "skip" of the next scheduled glaciation. )

    Alex , if you have some definite contrary evidence (i.e. a scientific paper in a respected journal) then please cite it.

    Alex , your third paragraph is rather jumbled in its ideas.  Could you please clarify what you mean?

    On your fourth paragraph:   I would be interested to hear whether (and how ) you would compare the dangers to humanity from the present-century very rapid global warming . . . compared with the dangers to humanity from a very slow ( 10,000 to 20,000+ years' duration ) of global cooling.  [Though this cooling scenario has now become abstract & hypothetical.]

    Basically, I am thinking that 10,000+ years is plenty of time for the human race to find technological solutions in dealing with such cooling . . . or perhaps even to revert to low-tech methods such as the well-proven anti-cooling technique involving burning a small number of gigatons of coal !

    On the other hand:  for dealing with the immediate & very pressing problems of rapid global warming during the next 50+ years ~ our politicians seem paralysed like rabbits in a spotlight.

  22. "Secondly, there is no hard data offered in this argument to show why the tilt and orbit are weak for this time period."

    I am not I following this. The astronomical cycles are very strongly established by observation (look up Milankovitch cycles or see the animations here). The effects on irradiation of the surface were calculated by hand by Milankovich (while in jail from memory) and have been repeated and checked numerous times.

    An analysis of the current glacial cycle is in Berger 2002 but rather moot given our CO2 levels. Remember that Milankovich cycles have been around for a long time, but can only induce glaciation when CO2 levels drop to level where summer snows dont melt at around 65N during low irradiation. The last time we had 400ppm was pliocene and there was no glacial cycle.

  23. Thanks for your posts. I'm starting to see your points on this. 

    In the past, the orbital cycle must've had enough effect to start a feedback loop to begin the glaciation cycle. As the ice sheets grew, it reflected more and more solar energy. At the same time, carbon based life increasingly died off due to the temperature change, trapping CO2 on earth. When the orbital cycle reversed, all of this CO2 was released back into the atmosphere again through its own feedback loop (life begetting more and more CO2). This warming feedback loop is also proof that CO2 plays a very large role in warming as there is no other reason to explain how the temperature could spike so much during the interglaciations.

    Now in the last 150 yrs or so...Humans have created a new mechanism which allows for a substantial amount of pre holocene CO2 (which was trapped deep under the ground) to be emitted back into the atmosphere....and this likely has altered the normal feedback loops we have seen in the data for the holocene.

    Since there is so much CO2 in the atmosphere now, these cycles may now likely be broken and meaningless as our CO2 concentration are out of the norm for the holocene. This makes sense to me given that we are using CO2 from periods(jurassic, etc.) where temperatures were much hotter then the holocene.

  24. Ralph Ellis suggests that the warming that ends glaciation is not from CO2 greenhouse effect, but instead dust storms cancelling albedo on northern ice sheets. He proposes that the inertia of natural cycles is towards glaciation: cold orbit forcings eventually start ice sheet formation, which adds albedo, which adds cold & more ice sheets, etc. When it gets cold enough, oceans draw in CO2, and at a critical point (low enough temp & low enough CO2) rapid plant death ensures at certain elevations. This allows for erosion / dust storms, which land on ice sheets to cancel their albedo. Although the dust effect he speaks of would not have as widespread effect throughout the world, it would have a local strong effect on the ice to break the feedback process. Because the critical cold temperature may take several Milankovitch cycles to reach, his theory may explain why not all Milankovitch spike result in glaciation escape. I’m curious what experts think about his theory. (I am not an expert.) To me it seems to make sense and seems like a very disciplined paper. Maybe he uncovered the a key strong variable for escape of glaciation.

    In light of his dust-albedo cancellation being a strong effect, Ellis then concludes that CO2 is too weak to threaten overheating us or runaway greenhouse effect, and we shouldn’t worry about it… afterall CO2 of 280 ppm had too weak an effect (about 3.7 W/m2?) to prevent entry into glaciation. Ellis suggested that its almost like we were put here to burn fossil fuels to prevent an ice age.

    I hesitate to follow him to all of his conclusions though. For one, why the two must be mutually exclusive? If his strong local “trigger” indeed matters more for glaciation exit, why must CO2, which is cumulative, lasting, global, & rapidly rising not matter at a high enough level in our situation? I’m most concerned that temp is quickly rising despite cooling forces from solar & orbital cycles… and we’ve only begun to make CO2 at a very rapid rate.

    In terms of “preventing an ice age”. Many above suggest we’ve already prevented or much delayed it. Also, many above suggest, CO2 is like a gas pedal that recoils slowly once pressed. Future generations could always press the pedal further if determined necessary for ice age avoidance thousands of years in the future. But if we determine that we’ve pressed it too far, and are now in danger… too late. Can’t draw CO2 down rapidly.

    I’m no expert though… so I’d much appreciate an expert’s reflection on the significance of Ellis’s paper.

    http://science.uwaterloo.ca/~mpalmer/stuff/ellis.pdf

  25. Lawrence Tenkman @399,

    While I'm not familiar with the paper you enquire about, Ellis & Palmer (2016), I note it not referenced by the likes of Willeit et al (2019) (which may be why I've not encountered it before).

    On the subject of dust-driven albedo forcing, the Ice Age cycle does present one puzzle addressed by Wileit et al and that is the mid-Pleistocene transition - when Ice Ages changed from a 41ky cycle to a 100ky cycle a million years ago. My (evident) weak understanding of the literature is that a potential candidate mechanism for the MPT rests with the repeated Ice Ages scouring the high-latitude landscape back to bare rock that then reduced the source of dust during the depths of an Ice Age and thus reduced the power of the negative dust-albedo feedback, this reduced power allowing Ige Ages to last 100ky rather than 41ky.

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