Arguments
Are we heading into a new Ice Age?
What the science says...
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Worry about global warming impacts in the next 100 years, not an ice age in over 10,000 years. |
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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)
At a glance
In something like a Day after Tomorrow scenario, the idea that a new ice-age was just around the corner was the subject of a book, a DVD and a website created in 2002. The author was a retired architect, by the way. Fortunately for us, both the movie and the quote above are figments of someone's fertile imagination. But let's have a quick look at ice-ages and what makes them tick, after which we hope you will agree that the notion that another ice-age is just around the corner is nonsensical.
Ice-ages, also known as glacials, are cold periods that occur in a cyclic fashion within an Icehouse climate state. Earth's climate has been mostly of the Hothouse type (no Polar ice-sheets). However, on occasion it has cooled down into Icehouse, as has been the case in the last few million years. There are regular variations in Earth's orbit around the Sun, taking place over tens of thousands of years. These affect the amount of Solar radiation reaching our planet. During the Icehouse state, such variations can lower and raise planetary temperature sufficiently to trigger swings between cold glacials – when ice-sheets expand towards the Equator – and mild interglacials – when the ice retreats back polewards.
To give an idea of the time-scales involved, Europe and North America have seen glacials and interglacials come and go repeatedly over the last 2.5 million years, this being known as the Quaternary Period of geological time. The last glacial period started 115,000 years ago and the Last Glacial Maximum (LGM), when the greatest ice extent was reached, was around 22,000 years ago. The current interglacial – also known as the Holocene, commenced 11,700 years ago.
A general pattern may be seen here with a long cooling down towards Glacial Maximum but a relatively quick warming into an interglacial. The speed of the warming-up part of the cycle is due to climate feedbacks. Removal of pale, reflective snow and ice cover revealing the darker ground beneath allows more solar heat energy to be soaked up. Melting of permafrost releases carbon dioxide and methane. These and other feedbacks serve to amplify the warming effect, speeding it up.
However, our burning of fossil fuels has happened on such a vast scale that we have blown such factors apart. The atmospheric concentration of CO2 has risen well above the 180-280 ppm range typical of recent glacial-interglacial cycles. The current level, getting on for 420 ppm, is more typical of the mid-Pliocene. That was a geological epoch that happened around a million years before the start of the Quaternary. Mid-Pliocene ice-sheets were much smaller than those of the present day. Rather than being due another glaciation, we can expect a continued transition towards mid-Pliocene conditions.
Please use this form to provide feedback about this new "At a glance" section, which was updated on May 27, 2023 to improve its readability. Read a more technical version below or dig deeper via the tabs above!
Further details
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? No.
To explore this topic further, it is necessary to understand what has caused the cyclic shifts between ice ages and interglacials during the Quaternary period (fig. 1). Such shifts are in part a response to regular changes in the Earth’s orbit and tilt, which affect the amount of summer sunlight reaching high northern latitudes and were described by the Milankovitch Cycles, first proposed in the early 20th Century by Serbian mathematician Milutin Milankovitch (1879-1958). For more about Milankovitch cycles this NASA page offers lots of graphics and explanations.
Figure 1: Temperature change through the late Quaternary from the Vostok ice-core, Antarctica (Petit et al. 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.
When incoming sunlight declines in the high north, the rate of summer snow and ice-melt declines and the ice sheets begin to grow. When incoming sunlight increases, the opposite happens. So where are we in these cycles today? Changes in both the orbit and tilt of the Earth do indeed indicate that – were they singularly responsible for climate shifts - the Earth should be slowly cooling. However, recent research shows that is too simple. That's because we now have analyses of ice-cores going back 800,000 years or more. We have devised ways to use stable isotope ratios of various elements in things like fossils and we have developed many other proxy methods for telling us more about conditions in the relatively recent past that the Quaternary represents.
A number of irregularities in glacial-interglacial cycles have been determined, for example times when interglacials were skipped when orbital patterns suggest they should have happened. (Koehler and Van de Wal 2021). Such research has also been aimed at resolving the question of why Earth's 41,000 year obliquity cycle was a strong driver of glacial-interglacial transitions up until around one million years ago. Since then, glacials have instead typically lasted for much longer - around 100,000 years.
The importance of feedbacks within Earth's climate system has been increasingly recognised as the decades have gone by. A good example is the speed of transition from glacial to interglacial, which is relatively rapid because certain very effective climate feedbacks are involved. One such feedback involves albedo, defined as the ability of different bodies to absorb or reflect sunlight (e,g, Thackeray and Fletcher 2016).
Albedo is expressed on a scale of 0 (black body, absorbs everything) to 1 (white body, reflects everything. Fresh snow has a high albedo of as much as 0.9, whereas the muck revealed when old snow and ice cover melts has a much lower one in the range 0.2 to 0.4 – it can absorb lots more solar energy. So melting snow and ice leads to more heat energy retention, amplifying the warming (Fig. 2).
Fig. 2: Albedo feedback explained. Freshly-fallen snow is highly reflective of incoming sunshine, so that most of the solar energy is simply bounced back towards space. Bare sea ice can potentially absorb about half of the incoming energy, so if conditions become warmer, causing the snow to melt, there’s more energy retained on Earth. If the sea ice melts too, then almost all of the incoming solar energy is absorbed by the much darker surface of the sea. So an initial warming directly results in further warming. Graphic: John Mason.
Another feedback happens when permafrost gets thawed out, since the ground is then able to release previously trapped CO2 and methane. During a glacial, the extent of permafrost is vast, so as it thaws, the release of such gases occurs on an enormous scale – again, amplifying the warming.
Researchers have also modelled ice-sheet dynamics, investigating how the sheets behaved as they melted, for example. It has been found that the shorter-lived, lower latitude Northern Hemisphere ice-sheets that existed prior to one million years ago were much thinner and therefore easier to melt. So ice-sheet dynamics looks to have a role in the much longer freeze-ups of the past million years. This all goes to show that glacial periods arise through a whole lot of factors interacting with one another, of which orbital cycles are but one, albeit important, cog in the gearbox and are not necessarily able to drive the climate system from one state (glacial) to another (interglacial) in total isolation (e.g. Bintanja and Van de Wal 2008; Berends et al. 2021).
Talking of cogs in the gearbox, we are another – and a big one. Our intentional disturbance of carbon reservoir rocks – what we do when we seek, extract and burn the fossil fuels – is unique in the geological record. It's a one-off in the planet's 4.56 billion year long history and while the consequent overloading of atmospheric CO2 levels is still insufficient to take Earth back into a Hothouse state yet, it is perfectly adequate to prevent another glaciation any time soon.
Last updated on 27 May 2023 by John Mason. View Archives
To my mind, this is denial of physics. You cannot change CO2 concentration without affecting the radiation at surface. Furthermore you have the problem of synchronous glaciation in Southern hemisphere which is easy enough to explain with change in CO2 being driver. Methane and isotope populations in ice bubbles also point to importance of eurasian wetland in the CO2 budget. This is not deny that dust is also important part of the feedback mechanism. I havent read paper, but is it implying that lowering CO2 is responsible for reduced vegetation? Any evidence of this in tropical regions? To me, it sounds handwavy and selective in the evidence that the hypothesis is using.
MA Rodger & Scaddenp,
Thank you so much for your quick responses.
MA Rodger, very interesting. So dust-albedo blunting has always been a proposed mechanism for glaciation escape, but perhaps at MPT, the source for the dust “dried up” so it stayed cold longer? Ellis says MPT is beyond this paper’s scope, but he has a line suggesting that elevation of the Himalayas may have influenced MPT. Ellis suggests the earth beneath dying forests as a source for dust. His theory is: forests die from combination of low temp and low CO2 (both of which lower at higher elevations). I was just curious of what you thought of the correlation he found with dust in his graphs at the end. The paper’s first page or so lays out his premise. The charts and graphs are interesting, especially the one at the end where it shows temperature & CO2 drop, followed dust formation, followed by temperature rise. I thought it looked convincing. But I lacking the knowledge most of you have, am not qualified to critique it. If you have a moment, would you mind?
Scaddenp, your response draws on knowledge that I don’t have (synchronous southern glaciation showing CO2 being driver), and thus I cannot follow. Forgive me. I'm not sure what you mean about the denial of phyiscs. I know CO2 air concentration can affect temp (greenhouse) and temp can affect CO2 air concentration (water solubility). (Is that what you were referring to?). Ellis says that going into glaciation, temp drop caused CO2 drop. He says CO2 was 190 ppm, but it got low enough to affect trees at certain elevations (where partial pressure is low enough to reach a critical level of 150-160). He has a chart showing temp and CO2 concentration at various elevations in tropical and alpine regions. So far, I’m impressed with his data, but hesitant with his conclusions (in light of other overwhelming data)… but my level of knowledge makes my critique of limited value.
My goal is to read this entire website… this happens to be just one nugget I’m trying to digest at the moment.
"Ellis then concludes that CO2 is too weak to threaten overheating us or runaway greenhouse effect, "
This statement. But I guess could be more nuanced. He is right that burning every piece of fossil fuel will not cause a runaway greenhouse, but "overheating" is a subjective judgement. It is certainly capable of raising average global temperatures beyond 4C.
Lawrence Tenkman @402,
I do hope to get round to giving Ellis & Palmer (2016) a read through but it isn't the shortest of papers & gives the impression of not being so well set out for a quick skim-through.
On the subject of dust and Ice Ages, as much of the data which folk play with is derived from ice cores and dust is one of the things found in ice cores, it isn't too much of a leap to understand where all the dusty theorising comes from. Some other examples of dusty theorising include the likes of Alfredo Martínez-Garcia et al (2011) [described here] which proposes that iron-rich dust has a significant role in the ice age cycle and Simonsen et al (2019) [described here] who examine the local-origin dust as evidence of ice build-up in an Ice Age.
Lawrence Tenkman @402,
I did manage a read-through of Ellis & Palmer (2016). I note it isn't published properly which is likely why it fails to get mentioned within the literature. (It is published here but only as an “unedited manuscript” which was to “undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form.” I see no “final form.”)
There is within Ellis & Palmer mention of “another story for another day” with the suggestion that this would add to the grand theorising with explanations of Dansgaard-Oeschger events and the mid-Pleistocene transition. A paper co-authored by Ellis has appeared on the web explaining the pre-MPT 41ky Ice Age cycle as resulting from there being an extra southern-driven version of the Ice Age cycle which post-MPT ran out of land in the post-MPT permanently-iced-over Antarctica and leaving only the northern-driven post-MPT 100ky Ice Age cycle.
I'm not sure how the pre-MPT cycles would fit in with the Ellis & Palmer theory of dusty interglacial-triggering. (The appearance of interglacials in beat with the orbital eccentricity wobble is described in this follow-on thesis as purely coincidental. The frequency is defined by the 70ky it takes to prime the system with ice.)
The absence of proper follow-on work, of publication or of citations is a kiss of death to theories such as set out by Ellis & Palmer. But that does not explain what it says or why it is wrong to say it.
Ellis & Palmer (2016) is a poor piece of work. It occasionally says some very silly things but I shall ignore those. It also gallops past the science rather than addressing it, indeed describing it as “scientific lacuna.” But I shall here ignore such hubris.
The grand theory presented explains that the precession/obliquity within the Milankivitch cycles does not always lead to an interglacial and that this is not immediately explained by CO2/albedo alone. To cause an interglacial Ellis & Palmer invoke a dusty atmosphere which reduced ice albedo and, as warming takes hold, adds to this albedo reduction when warming brings greater levels of dust to the melting ice surface.
They say the dust results from reduced CO2 which causes lower tree-lines globally and this increasing dust as plant-less dusty mountain tops grow into dusty mountains and then dusty hills with the lowered tree-line. A correlation of dust and CO2 is presented. This dust-correlation could be made with many other different factors so is effectively an exercise in curve fitting with the low-CO2>>high-dust relationship remaining speculative.
What is also not explained in all this is the mechanism driving the CO2 reduction and why this cooling doesn't keep on going. The peak-dust levels do not appear to have a threshold level and if there is a CO2/ice-volume/Milancovitch/dust mechanism at work it has yet to be convincingly demonstrated.
So without further work beyond those referenced here, work to fill in the gaps and thus enable this allegedly important theory to be properly published, it is fair to say that not a great deal has been done since the initial appearance of this work in 2015 which was then, with its parting comment “So the only evil in this world is not in the atmosphere, it lies in the hearts of those who wish to starve plants and animals of their most essential food supply — CO2. “, certainly more work concrened with denialsim than with scientific analysis.
MA Rodger , geoengineering climate by distributing iron (as fertilizer) to pelagic ocean, has been discussed in previous years.
Tim Conway & Seth John (2014, Nature ) indicated that a large proportion of North Atlantic ocean-water iron was deriving from Saharan dust.
There has been some more casual discussion of the idea of dust from dry land similarly producing algal bloom and thus a reduction of atmospheric CO2. This climate-cooling mechanism (which I have not seen quantified) would act in opposition to the dust-albedo mechanism suggested by Ellis & Palmer (2016) .
Scaddenp & MA Rodger,
Thank you so much for your responses.
MA Rodger, thank you for reading that article an phelping me with it. Please clarify a few things for me if you don’t mind. You mentioned that "Ellis & Palmer fail to explain the mechanism driving the CO2 reduction and why this cooling doesn't keep on going… and that the peak-dust levels do not appear to have a threshold level." My impression from reading was they propose Earth gets cold enough at the nadir of orbital Milankovitch cycle to start forming ice, and if enough ice forms, albedo is sufficient resist subsqeuent Milakovitch warming cycles, and Earth plunges into into a glacial period via increasing of both ice formation & ice albedo feedback. Ellis & Palmer suggest CO2 falls because the cold makes the ocean draw CO2 in (increased solubility of the cold water) and this CO2 drop is what stops further cooling, b/c plant death from low CO2 & low temp causes the dust.
It all sounded interesting to me… but even if their theory about dust were true about glaciation exit mechanisms, I don’t think it would be right to conclude that infinitely high man made CO2 & greenhouse doesn’t matter in today's world. This website has so much data suggesting we need to care.
I’m not sure what you mean by: "the peak-dust levels do not appear to have a threshold level." What does that mean? Threshhold referring to a temp or CO2 level at which dust forms? Threshhold referring to a level of dust at which it is can melt ice? I thought the dust elevations seemed to occur during temperature & CO2 nadirsand seemed to precede warming consistently.
Ellis & Palmer’s parting comment wasn’t in the website link I had (http://science.uwaterloo.ca/~mpalmer/stuff/ellis.pdf) (“So the only evil in this world is not in the atmosphere, it lies in the hearts of those who wish to starve plants and animals of their most essential food supply — CO2.”). But on YouTube, I did hear Ellis suggest we may be put here by “intelligent design” to burn fossil fuels to save us from an ice age. Sounded a bit off to me…. and made them seem quite biased. Hence, I wanted to hear from someone more educated that me on these concepts. Thank you so much for discussing this with me.
Lawrence Tenkman @407,
To clear up the "parting comment", it appears in a 2015 blog-post linked at the last paragraph of #405 above. The denialist flavour of this "parting comment" does explain some of the very odd comment in Ellis & Palmer (2016).
The 'CO2 mechanism' I say is not explained is specific to the glacial maxima. Ellis & Palmer (2016) demonstrate temperature, dust and CO2 are correlated (in their figs 1, 4, 8 & 9). We could also include sea level/ice volume and methane into such correlations. So the question arises - What is driving what?
During the drop into an ice age we can be reasonably confident that reduced northern insolation allows a build-up of northern ice sheets reducing regional albedo which has a global impact on temperature and kicks-off positive feedbacks in albedo, CO2 & methane.
But the glacial maxima appear to have a particular pattern to them, perhaps clearest when sea level is considered. The Ice Ages step up a gear as they dive into the maxima.
Ellis & Palmer point the finger at the CO2 feedbacks. They would have difficulty using albedo as the dust-levels are building at these points in the Ice Age cycle and Ellis & Palmer dismiss the idea of atmospheric dust-levels being a significant cooling factor.
Given the constraints placed on the workings of Ice Age maxima by Ellis & Palmer, their hypothesis seems to rely on some strong CO2 feedback that comes into play at this point in the Ice Age cycle. So my question - Are the measurements of CO2 showing a big enough reduction? What is causing these large reductions in CO2? And what causes these reductions to quickly reverse when the maxima is over?
And not greatly removed from any discussion of 'CO2 mechanism'....
Regarding the lack of 'threshold' for dust levels to bring Ice Ages out of their maxima, Ellis & Palmer Fig 4 (below) shows great variation in the peak level of dust as well as variation in the duration of high-dust prior to the glacial maxima. This I term a lack of 'threshold'. The general impression is that a generally high level of dust reducing albedo of global ice sheets awaits the increase in nothern insolation caused by the Milankovitch cycle.
But surely this variability means the power of the dust-reduced albedo forcing is not strong enough of itself to be the trigger. It is possible that analysis would show the Milankovitch cycle and the dust-albedo in combination provides a consistent threshold level, or perhaps CO2 levels are also a factor in the mix. But such necessary analysis would require an approach somewhat less simplistic than Ellis & Palmer. (For instance, compare the Ellis & Palmer approach with that of, say, Willeit & Ganopolski (2018).)
I think that covers the issues from #407, hopefully in an understandable form.
MA Rodger,
Thank you so much for your kind resopnse. I much appreciate you. Very interesting. So complex.
It seems that the article by Willeit & Ganopolski (2018) suggest that much dust comes from the equatorial advancing edge of the glacier (erosion from the advancing ice edge as I understand?)… not necessarily plant death as Ellis & Palmer suggest. Also, albedo blunting for glaciation escape is not accomplished by dust alone… albedo is increasingly blunted by the increase of both snow age & of dust accumulation, combined together. Perhaps this explains the lack of a critical level for the dust as a single factor blunting albedo… as multiple factors that combine to do it.
Those equations made my head hurt. I feel like a patient sitting in a doctor’s office asking questions and expecting them to make me understand concepts it took years of medical school to understand. For sure, that’s not possible, as I’d have to go through all the training you did… year by year ... more answers leading to more questions.
But I do appreciate you very much. Thank you for taking the time. Thank you for doing what you do.
LT
Recommended supplementary reading...
Video interview of Ian Plimer at Sky News falsely claims that a new study announces an incoming ice age, partly based on an incorrect Daily Mail headline, Edited by Nikki Forrester, Article Review, Climate Feedback, Jan 20, 2021
Please note: the basic version of this rebuttal has been updated on April 16, 2023 and now includes an "at a glance“ section at the top. To learn more about these updates and how you can help with evaluating their effectiveness, please check out the accompanying blog post @ https://sks.to/at-a-glance
Thanks - the Skeptical Science Team.