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
@jhnplmr:
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JH: Fair enough.
jhnplmr: I have replied on a more appropriate thread.
[JH] Thank you.
"Response:[RH] Fixed image width.
What should I do next time I use an image?
Response:[JH] Keep your graphic width to 500 pixels or less."
Wouldn't it have been easier to say this in the first place?
[JH] Lose the snark or lose your posting privileges. No more warnings.
#349 HK
If you want to duplicate the graph I displayed on #339 you will find the temperature data on edc3deuttemp2007.xls. This gives EPICA Dome C ice core temperature differences from the 1000 year mean temperature (col 5). The age of the sample is given in col 3.
The Jul 65N Milankovitch data was drawn from orbit91 for the years BP and the data for the 10,000 years into the future was derived from the mean values of Jul 60N and Jul 70N in bein11.dat. A correction factor had to be used for the future years to give the same zero year point. I used 0.479775 instead of 0.4843 to convert langleys/day into W/m2. This gives an error of less than 1% in the absolute data but does not effect the date of the minimum point. I used the formula "=PRODUCT(AVERAGE(DV15:DV16),0.479775)" on my spreadsheet where DV15 and DV16 are the cells holding the relevant data. The location of these cells will obviously alter as you go down the spreadsheet but *intelligent copying" will make this easier.
#349 HK
"That’s why much of the last glaciation endured through higher insolation than today without ending"
The sun reflecting off the widespread ice sheets offset the effects of the higher insolation. This positive feedback from the ice acts both ways, it slows the rise out of the glacial period but accelerates the rise once the ice sheets start to melt and less of the sun's power is reflected.
jhnplmr... It actually is stated in the comments policy how to post images. But don't worry about it. Lots of people make the same mistake and we just fix it.
jhnplr:
I didn’t bother to duplicate your graph, just inverted it (better with time running from left to right, don’t you think?) and adjusted it a bit.
First of all, let me emphasize that I’m not a sceptic of the Milankovitch theory in general as it fits the temperature data quite well. And the reason why the summer insolation in the north seems to control the climate in the south is clearly related to the fact that the albedo feedback from ice sheets and vegetation is much larger in the north.
As explained earlier, the main reason why I don’t believe in a new glaciation within the next few millennia is that the summer insolation in the north won’t drop much further before starting to rise again in 2-3000 years. Let’s look at the graph and study the end of the last interglacial, the warm Eemian.
When the temperature had dropped to present level about 118,000 years ago (1) the 65N July insolation (2) was already lower than during the Last Glacial Maximum about 20,000 years ago! It was in fact lower than at any time during the last 110,000 years, except for a short period about 70,000 years ago. When the insolation reached it minimum 3-4000 years later (3) after a drop of nearly 100 watt/m2 from the peak, the temperature (4) was still comparable to the level 14,000 years ago – when the insolation was almost 60 watt/m2 higher!
It clearly takes a large increase of insolation to pull us out of a glaciation once it has started and a large decrease to initiate a new glaciation from an interglacial. The next few millennia will not give us that large decrease, but some of the CO2 we’ve already emitted will stay in the atmosphere long enough to keep the concentration above 300 ppm – highest for 800,000 years – until the insolation start to rise again.
The claim that early agriculture and deforestation may have prevented or delayed the next glaciation is an interesting theory. We shouldn’t dismiss that early humans may have had a significant impact on the environment despite their primitive technology if given some tens of millennia considering what we have done in only a few decades. But some of these impacts, deforestation and desertification from overgrazing, have increased the Earths albedo and therefore acted as a negative forcing. I don’t know if the positive forcing from a few more ppm of CO2 was enough to counteract this. Maybe no one knows for sure, but it’s an interesting topic.
Its worth pointing out that the other thing you need to turn a local NH glacial event into a global event, is to pull down the GHG levels. See Hansen and Sato 2012 (esp Fig2). NH Albedo change only really affects NH climate.
How is Figure 4 determined?
(-snip-).
[DB] Figure 4 is based directly on Figure 3 from Archer 2005.
Sloganeering and arguments from personal incredulity snipped.
The link to Archer 2005 is stale. Here is a new location of that paper: http://geosci.uchicago.edu/~archer/reprints/archer.2005.trigger.pdf
Climate Dialogue has a good and recent overview of the potential effect of a new Maunder Minimum, in its "Introduction" to that topic.
Will somebody please add to the Further Reading section of this post, a link to Ari's bibliography of readings on future glaciation?
The fact is that through out recorded history a significant increase in Volcanic activity along with a weak solar maximum has always been a precursor to an Ice Age. Anything that has skeptical in its name is bullshit. They are skeptical about the truth and the evidence that goes with it.
[PS] Welcome to Skeptical Science. Please take your time to familiarize yourself with the Comments Policy. Conformance in not optional. Please in particular note the prohibition on sloganeering. If you wish to challenge the science, then do so with evidence, preferably from peer-reviewed sources. Thank you.
Echo_Alpha @363, evidence please. Or are you only interested in sloganeering?
Echo_Alpha... Then if it's a fact you should be able to show us the research that supports that position.
I don't see how the author of this thread can say the next ice age is 10,000 years away. I see from the graph at the top of this thread that the previous interglacials were all very short, and it appears from the green bars on the graph that the Holocene is already longer than any of the past 4 interglacials. What evidence is there that we can expect 10,000 years of Holocene?
[TD] Read the text. Then click the Intermediate tab and read that text.
As you can see the data provided by SS proves that this is not the first time temperatures have reached this point. Just like the upcoming ICE age will not be the first time Tempertures dropped significantly after a decrease in solar activity and increase in volcanic activity. Yes we are in deed headed for another Ice age.
[JH] Sloganeering snipped.
CO2 levels are now above 400 ppmv, 33% higher than at anytime in the last 800,000 years:
Of course HydrogenOne concludes from this that temperature in the Eemian was similar to that today, and in the face of strong orbital forcing, it fell back into an interglacial, the much stronger CO2 forcing, and much weaker orbital forcing today will also drive us back into an interglacial. No doubt it is the massive loss of NH albedo due to the loss of sea ice that convinces him of this:
(2012 Aug arctic sea ice (purple) overlaid on 1938 Aug arctic sea ice.)
From the time-stamp history of the past 368 comments I see a drastic slow-down in discussion of this topic in the last 4 years. Is there a better "Arguement" topic in which to post regarding this topic?
[JH] Enter "Ice Age" in the search engine and take your picks among the articles that are listed.
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Thanks JH and PS. This topic appears to be the most relevant to my question, and my apologies as a newbie if it has already been debunked somewhere in the past 360-odd comments.
I am familiar with the arguments against a new ice age coming any time soon submitted by Anne-Marie Blackburn (the discussion of the <href="https://www.skepticalscience.com/Milankovitch.html">Milankovitch Cycles and the CO2 emissions override to which Daniel Bailey added the effects of solar insolation contained in the header's Intermediate tab.
My idea comes as old memories from research I made in preparation for my 7th grade geography class term paper on the ocean floor in 1962. At that time I had read a 1958 article published in Harpers written by Betty Friedan called "The Coming Ice Age" that proposed that an open water Arctic Ocean could essentially jump-start a new ice age by saturating the usually very dry Arctic air with moisture that would in turn increase winter snowfalls to the point that increased albedo from snowpack in the northern hemisphere would create a feedback loop that would continue the snowfall throughout the year in these latitudes.
Of course, if you read that entire article you can poke holes in all manner of the supportive evidence since the science at that time was just in its formative years. But, I wonder about the central premise because the catalytic state of an ice-free Arctic Ocean is soon to be achieved. And, just as one releases the choke on one's snowblower after getting it started, I wonder if the world's now-underway switch from fossil fuels to renewables (turning off the choke) will remove the CO2 threat over the next century just at the time when it would be helpful to mitigate against the snow cycle about to come. I would appreciate your views on this idea.
The first hyperlink above was mistyped and should be Milankovitch Cycles. The second link to "The Coming Ice Age" is not directed properly and I don't know how to fix it. The Harpers URL works only sporadically, so to those interested in this bit of ancient history I can only suggest Googling a term such as "The Coming Ice Age Harpers" and look for the link in the search results. My apologies for this inadequacy. Another good book for detailed descriptions of Blackburn's original response submission is the book The Ice Chronicles by Paul Mayewski et. al., 2002.
Dave, I have a couple of objections to idea that ice-free arctic would trigger an ice age.
Firstly, an historical look (something not known in 50s). Last time we had 400ppm of CO2 and open water was Pliocene and we didnt have an ice age cycle then (but still have milankovich cycles).
But why?
A warming world will certainly have more precipitation and for cold, wet parts of the globe it will certainly mean heavier snow falls. However, an open arctic ocean is still freaking cold so the contribution to water in the atmosphere from arctic basin is small compared to the warmer oceans elsewhere. An open arctic isnt going to be trigger point.
But could thick snows more than offset the albedo loss from having dark water instead of ice in the summer arctic ocean? The forcing of the ice ages from Milankovich cycles implies that critical factor is persistance of snows around 65N through summer. In cold part of the cycle, there is not enough radiative heat to surface to melt the snow. The summer extent is more important for global albedo than winter. Summer extent continues to decrease implying there is more than enough heat to melt the winter snows even as they get heavily.
DaveMartsolf @372, adding to scaddenp's comment, I would note that Flanner et al (2011) measured the albedo feedback from snow and ice between 1979 and 2008 (see here for discussion). As can be seen from the second panel of the figure below, the only month in which the albedo feedback had increased over that period was October, and that by a very small amount. It in no way compensates large increases from March through to July:
A more recent review finds a global Snow Albedo Feedback of 0.1 W/m^2 per degree K, but that is significantly increased over spring, amounting to a 1% decrease in surface albedo per degree K over spring.
In either case the effect of a more open Arctic sea has been to decrease the snow albedo effect, resulting in further warming. That has been despite some indications of a thicker snowpack in the depths of winter, particularly January. The increased snow depth in winter has minimal impact because winter days are much shorter in the relevant latitudes, and the sunshine weaker durring those days. Despite the thicker snow pack, however, it continues to melt earlier, just as the sunshine strengthens and the days lengthen. The result is an overall increase in albedo. There is minimal effect in the late summer because by that time nearly all the snow pack, except at high altitudes, has already melted.
Overall, Anne-Marie Blackburn's idea, as described by you, is an interesting one, but appears to be failing the empirical test. It also contradicts the current understanding of the causes of glacials and the end of interglacials. In relation to the later, and as shown by the Vostock and Epica C ice cores, declines from interglacials to glacials tend to be long drawn out affairs (unlike the very rapid transitions from glacial to inter glacials). That is the opposite of what would be expected if Blackburn's idea had merit:
Tom, I think you are confusing Betty Friedan (author idea that open arctic might trigger ice age), with Anne-Marie Blackburn (Sks author of Milankovich article).
scaddenp @374, I was, and apologies to both ladies.