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
# 320 Tom Dayton
"we could prevent a glacial period with a single chlorofluorocarbon factory for the entire world"
You surely don't advocate such a method, it would have a catastrophic effect on the ozone layer. The manufacture of such compounds has been phased out by the Montreal Protocol.
"But as other people already have told you, our greenhouse gas increases to date with just the next couple of decades will be sufficient to prevent cooling, let alone glaciation, for thousands of years"
This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades. Solar insolation will remain unchanged, the present level (426.76W/m2) was sufficient to reduce ice core temperatures 4 deg C below current levels at a similar point in the cycle 115,000 years ago.
jhnplmr:
"This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades."
What scarcity? According to this figure from James Hansen’s Climate Change and Intergenerational Justice (not yet published) the reserves are huge, particularly of coal and unconventional gas. If the estimates of recoverable resources (>12,000 gigatons of carbon) are approximately correct and half of that was released at once, it would raise the CO2 concentration by 3000 ppm. If it was released gradually and the airborne fraction remained close to 50% (not very likely) we are still talking about 1500 ppm in addition to the 400 we already have.
If that happened, the CO2 level would remain above 600 ppm for 5000 years, enough for a complete melt-down of Greenland and West Antarctica and maybe East Antarctica as well.
You can test it out for yourself with the GEOCARB model. If you set the transition CO2 spike to 3864 gigatons, the simulation will start with 1900 ppm CO2 in the atmosphere.
jhnplmr wrote "This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades."
jhnplmr, you keep repeating that contention without responding to the factual counterpoints that a bunch of people have been making. For example, I pointed you to a peer-reviewed study in the original post that this very thread is on, showing the tiny temperature consequence of a 1 W/M^2 drop in global (not just at 65N) insolation. You could have gotten more details at the link provided in this original post, where you would have read that even in the optimistic greenhouse gas emissions reduction scenario A1B temperature would continue rising well past the year 2100.
I and other people have given you data showing that just the quantity of greenhouse gases that already are in the atmosphere are sufficient to prevent cooling to pre-industrial levels for at least many decades, and that's if all emissions instantly went to zero, which has a probability of zero. Reducing CO2 levels takes much, much longer than raising them (the "long tail"), so every single year that we keep increasing levels means we are delaying their dropping back by about ten years. See the SkS post "Global Warming: Not Reversible, but Stoppable."
You seem to be intentionally missing the point of the example that a single chlorofluorocarbon factory could delay the next glaciation indefinitely. That example illustrates how little greenhouse gas emission is needed. We don't have to use chlorofuorocarbons. We could use a larger amount of CO2, but an amount that still would be trivial to produce, even when fossil fuels become much scarcer.
The bottom line is that your contention is factually incorrect, that preventing cooling would be expensive and difficult.
jhnplmr, after you read the Global Warming: Not Reversible but Stoppable post, you should read A Glimpse at Our Possible Future Climate, Best to Worst Case Scenarios. Skip past the first section.
#321 HK
"As you see, the insolation will decrease only marginally during the next 2-3000 years before it start increasing again"
I agree, my graph shows the same, it should, we used the same data except that I calculated 65N as the mean of 60N and 70N to get one graph. We also seem to agree now that the minimum will occur in 2000 years time.
"AGW has not only stopped the long-term cooling trend that culminated with the Little Ice Age, but has already brought the global temperature back to the level of Holocene optimum 5-8000 years ago."
This presupposes that present levels of GHG will be maintained, my contention is that they will decrease as the fossil fuel scarcity starts to bite in the next few decades. Solar insolation will continue to fall, albeit by not very much, dragging down the temperature with it. After the minimum is passed temperatures will rise again, hopefully at GHG levels far below the present.
jhnplmr, multiple people repeatedly have shown you data that the insolation decrease you are fixated on (and, bizarrely, you are hyper-fixated on 65N) will have a tiny effect on temperature--an effect too small to worry about for thousands of years, and one that can be offset by a trivial effort to put more greenhouse gases in the atmosphere.
Your incessant repetition of your contentions without responses to factual counterpoints is sloganeering. From the SkS Comments Policy: "No sloganeering. Comments consisting of simple assertion of a myth already debunked by one of the main articles, and which contain no relevant counter argument or evidence from the peer reviewed literature constitutes trolling rather than genuine discussion. As such they will be deleted. If you think our debunking of one of those myths is in error, you are welcome to discuss that on the relevant thread, provided you give substantial reasons for believing the debunking is in error. It is asked that you do not clutter up threads by responding to comments that consist just of slogans."
327 HK
"What scarcity?"
Fossil fuel depletion is as controversial as global warming!
Here are some estimates:
peak_oil.html
Current estimates for the world wide peak production, not only for oil, but also for natural gas, and less traditional hydrocarbon sources range from the pessimistic (ASPO, 2007) to the less pessimistic (Edwards, 2001). The bottom line is that conventional oil and natural gas will probably peak sometime between 2010 and 2040.
Predicting_the_timing_of_peak_oil
In 2008, the IEA predicted a plateau by 2020 and a peak by 2030. The report called for a "global energy revolution" to prepare mitigations by 2020 and avoid "more difficult days" and large wealth transfers from OECD nations to oil producing nations. This estimate was changed in 2009 to predict a peak by 2020, with severe supply-growth constraints beginning in 2010 (stemming from "patently unsustainable" energy use and a lack of production investment) leading to rapidly increasing oil prices and an "oil crunch" before the peak.
It has been argued that even a "plateau oil" scenario may cause political and economic disruption due to increasing petroleum demand and price volatility
A 2010 report by Oxford University researchers in the journal Energy Policy predicted that production will peak before 2015.
Nicol-André Berdellé adjusted world oil production by deducting the energy equivalent of investments, and concluded that a more than doubling of investment in oil exploration and development between 2005 and 2010, masked a decline in net oil production. He argued that in net energy terms, peak oil has alrady taken place.
So most agree that peak oil will occur within the next decade, that is of course if the huge increases in reserves reported by most OPEC countries in the 1980's had any foundation in reality. I think that when supply is unable to meet demand there will be a very rapid depletion as nations stockpile the remaining oil. Unconventional sources such as shale oil take a lot of energy to extract and we will reach the point where we will put more energy into extraction that we gain from the product. Fracking has proved successful in the short term but the wells deplete very quickly and it is expensive to drill more. You point out the huge reserves left in the ground but most will never be extracted due to the energy requirement to extract them.
We have already closed down the last coal mine in the UK and are trying to minimise our use of coal for power generation in line with international agreements.
I think that all these factors will result in a decrease in GHG emissions during the next decades.
#331 Tom Dayton
"and, bizarrely, you are hyper-fixated on 65N"
That is because in an ice age Jul 65N Milankovitch cycles have a close correlation with global temperatures. there is nothing bizarre about it.
"No sloganeering. Comments consisting of simple assertion of a myth already debunked by one of the main articles"
The sources I have quoted are widely accepted, my interpretation of them differs from yours. That doesn't make you right and me wrong, only time will tell.
"It is asked that you do not clutter up threads by responding to comments that consist just of slogans"
You are right, this debate is no longer productive. I have stated my views that AGW has been beneficial in offsetting the falling Jul 65N solar insolation since the last peak 10,000 years ago. This has served to prevent a fall in global temperatures and has extended the current interglacial period. I have quoted scientific articles that support this view. It is up to you to decide if these views have any validity.
I don't like threats so this is my last post on the subject.
jhnplmr claimed he is justified in using insolation at 65N latitude as the sole predictor of global temperature in the next few decades to 2,000 years, because "in an ice age Jul 65N Milankovitch cycles have a close correlation with global temperatures."
No. That correlation is "close" only in the orders of magnitude of time and temperature of glaciations, as illustrated by Figure 2 in a Climate Data Information page--even when that figure admittedly has been "tuned" to make the temperature and insolation match as closely as possible. Just as CO2 is not the only driver of climate, neither is global insolation, let alone 65N insolation. You don't need a complex climate model to see that, as multiple comments and posts here have made clear. But you do need a climate model more complex than the single-predictor model that jhnplmr insists on using despite the overwhelming empirical evidence of its ineptitude for the application to which jhnplmr is putting it.
jhnplr:
Regarding peak oil
Let’s assume that CO2 will peak at 450 ppm with zero emissions after that. This is a very optimistic scenario since it only takes 20-25 years of our present emissions (no further increase!) to bring us to that point. What will happen?
In that scenario, according to the GEOCARB model, we will have 350 ppm of CO2 after 300 years and 300 ppm after 4000 years. 300 ppm is the highest level recorded in the ice cores during the last 800,000 years before the industrial revolution, so it’s safe to conclude that we have already cancelled the next ice age!
And that doesn’t include other man-made GHGs or natural emissions of CO2 and methane from thawing permafrost or methane hydrates. Also keep in mind that in 4000 years the summer insolation in high northern latitudes will be slowly increasing!
And further to peak oil, the climate problem is more about coal than oil, and we have an awful lot of coal available.
"According to BGR there are 1038 billion tonnes of coal reserves left, equivalent to 132 years of global coal output in 2012. Coal reserves reported by WEC are much lower - 861 billion tonnes, equivalent to 109 years of coal output." Source
jhnplmr... When people challenge your assertions you have to be able to either defend them, showing why you are correctly interpreting the information, or you have to be willing to accept that the challenges are correct and then adjust your position accordingly. Just stating the same thing when others have presented evidence to show you're incorrect isn't a viable position.
The thing that always gets me about fossil fuel reserves is that we know they can't sustain economic growth to 2100. Even if we take the higher figure of 132 years of continued coal use... that is at 2012 levels. Barring a massive decrease in population or economic collapse, electricity use is going to continue to skyrocket. By 2100 it will almost certainly be well over four times 2012 levels.
One way or another, our fossil fuel use is going to plummet this century. Most children being born now will live to see a low fossil fuel world... which could mean either a transition to clean sustainable energy or a polluted hellscape and massive economic and population crash. Even without AGW and other pollution problems, the need to get off fossil fuels is blindingly obvious... yet somehow there is still fierce resistance.
Fortunately, solar power is now becoming cheaper than coal for larger and larger portions of the planet. It seems likely that greed will save us from our own stupidity... but we're definitely cutting it close.
#334 Tom Dayton
"No. That correlation is "close" only in the orders of magnitude of time and temperature of glaciations, as illustrated by Figure 2 in a Climate Data Information page--even when that figure admittedly has been "tuned" to make the temperature and insolation match as closely as possible"
Yes, the correlation is close as you can see from my graph, and it is from raw data, not tuned as you suggest.
Look how the temperature rises in response the solar forcing at the start of the last interglacial. Look how it follows the peaks and troughs until finally we are dragged out of the glacial period into the current interglacial.
Notice after the peak, 10,000 years ago, temperatures (blue) start to fall in line with the solar insolation but then stop falling and start rising again before they level out and remain relatively constant. What could have caused this rise and levelling out? Could it be rising CO2 levels due to man clearing the forests (slash and burn) as he turned from hunting to farming and keeping domestic animals? The times certainly coincide. Could it be that the rising GHG from his activities are keeping the cooling at bay despite the falling solar insolation? If so, then his activities have been beneficial not an unmitigated disaster as you would have us believe.
If you don't believe that GHG emissions helped to counteract the falling insolation perhaps you can account for the rise and levelling out of the temperatures in some other way?
"But you do need a climate model more complex than the single-predictor model that jhnplmr insists on using despite the overwhelming empirical evidence of its ineptitude for the application to which jhnplmr is putting it."
Don't put words in my mouth, I have never said that solar insolation is the only forcing, my very first post on this forum said as much.
[RH] Fixed image width.
#337
Rob Honeycutt
"Just stating the same thing when others have presented evidence to show you're incorrect isn't a viable position."
Now you have given me the link to the graph I was referring to I have a new arrow for my bow. A picture is worth a thousand words. Thanks for that!
I don't know why my post was duplicated, the only thing new is the image. If this post is duplicated then something has gone wrong.
#334 HK
"300 ppm is the highest level recorded in the ice cores during the last 800,000 years before the industrial revolution, so it’s safe to conclude that we have already cancelled the next ice age"
I agree, the next glacial period is not going to happen, as for the next ice age, we have to get out of this one first!
By historic values the present levels of CO2 are low compared to those 500 million years ago when they were over 6000ppm Phanerozoic_Carbon_Dioxide. Sea levels were much higher but life was thriving. It has only fallen to current levels (393ppm) over the last few million years.
jhnplmr 500 million years ago the sun was significantly dimmer than it is now, so higher levels of CO2 were required to avoid a snowball Earth so that life could be thriving. You need to consider all of the forcings and consider the total energy budget.
Also just because life was thriving 500M years ago with higher CO2, does not mean that rising CO2 now is not a problem. The problem with climate change is a lot to do with the fact that it is a change from the climate to which we are heavily adapted (e.g. agricultural practices).
[TD] jhnplmr, for more information see the rebuttals to the myths "CO2 was higher in the past" and "CO2 was higher in the late Ordovician." See also "It's Not Bad." And if you want to argue with those posts, do so in the comments on those posts, not here.
#336 scaddenp
"And further to peak oil, the climate problem is more about coal than oil, and we have an awful lot of coal available."
I agree, coal generates more CO2 than oil, but coal usage is falling. We have closed down the last coal mine in the UK and we are trying to limit its use in power stations in line with our international committments. These measures, coupled to oil shortages over the coming decade, should help to decrease GHG emissions.
Fellas,
I think it's time to stop feeding this particular troll. He can't possibly be unaware that cities containing millions of people live on the coast. Sure, 'life' will thrive after those cities drown, but that's a facile argument not worth your time, and I doubt even he takes it seriously. He's not here to learn or even think. When you prove him wrong he shrugs it off without acknowledgement and offers a new <snipped>.
Happy for my comment to be modded out too.
Leto.
[TD] I deleted one of jhnplmr's most recent responses, because it went too far into irrelevance and ridiculousness by invoking stellar evolutionary timescale as evidence that our current greenhouse gas emissions are nothing to worry about.
#344 Leto
"and offers a new inaninty"
Perhaps you should learn to spell before you start insulting contributors. Why don't you start by telling me where I am wrong in the deductions I drew from my graph (#339)?
Response:[RH] Fixed image width.
What should I do next time I use an image?
[JH] Keep your graphic width to 500 pixels or less.
"These measures, coupled to oil shortages over the coming decade, should help to decrease GHG emissions."
Should and I certainly hope so. However, China and India are increasing coal use. Rising petrol prices will usher in electric vehicles, also good as far more efficient, but the electricity to drive them comes from what? The USA decrease in coal use is driven by shale gas. When that runs out, coal can increase in a perfectly free market. UK coal closures are driven by economics. My point was that there is no shortage of coal, plenty enough to create serious climate damage. If there is no limitation imposed on usage, and no alternative that is cheaper, then it will be burnt.
[JH] This discourse has gone off-topic. Please continue it elsewhere.
347 scaddenp
"Rising petrol prices will usher in electric vehicles, also good as far more efficient, but the electricity to drive them comes from what? "
Nuclear, wind, solar and tidal?
I agree, while it takes less energy to get it out of the ground than you can get from it they (we) will continue to use it. I'm afraid that it is very difficult to get people to stop heating their homes, using computers, electric lighting and their cars. It isn't going to happen while fossil fuel supplies are available. Any government that tried to ban their use would get voted out of office.
[JH] This discourse with scaddenp has gone off-topic. Please continue it elsewhere.
This guy isn’t particularly worried about the next glaciation. He claims that it’s unlikely to start until the summer insolation at 65oN approaches the same level as the onset of the last glaciation. That means in 130,000 years at the earliest and maybe not until 620,000 years. Note that it takes a much lower insolation to start a glaciation than to sustain it as soon as the slow positive feedbacks have been set in motion. That’s why much of the last glaciation endured through higher insolation than today without ending.
I adjusted his figure 3 to sum up his arguments:
[RH] Reinserted image to fix formatting error.
@jhnplmr & scaddenp:
I deleted your most recent exchange because it was completely off-topic.