Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


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)

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). 

Albedo Explainer (John Mason)

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

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.


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:


Denial101x video


Prev  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  Next

Comments 26 to 50 out of 410:

  1. There are a number of issues that affect a possible ice age - the sun (and related wobble to the earth) being one. The others include the melting of the arctic ice cap. With the ice in place, the climate is arid; with the ice melted, there is a source for water vapor - necessary for precipitation to happen. During the last major ice age, a portion of the arctic ocean remained open, thereby providing for a source of water for the snowfalls that covered North America (Russia on the other hand escaped glaciation). The third issue to be considered is a change to ocean currents - specifically the interchange of waters from the North Atlantic and the Arctic waters. It was noted in a number of studies in the 1930's that the arctic ocean was showing signs of warming.
  2. OK. This is what I have to say. I am not skeptical about the warming trend caused by atmospheric changes. I do think the current discussion in the media is limited. If we were about to enter an ice age, we might want more greenhouse gases to counter an ice age trend independent of the atmosphere and likely caused by astronomical features. The above discussion says an ice age is unlikely becasue of the warming forces. I say that gets to my basic point. The discussion is too narrow. Do not say "it is getting warmer, we must cool the earth." Ask what will come next? What should we do if the future will be warmer? and also ask "What should do if the trend is for cooler weather?" Our changes to the atmosphere must be in response to what we know about the climate in the future. Warmer will be inconvenient. Ice will kill most of us. I don't know what will happen. I know we need a wider discussion. Our most important question is "So what?" We need more data and a more comprehensive picture with many more questions. The cureent discussion in public is limited.
    Response: The question "so what?" is addressed in the positives and negatives of global warming.
  3. At this point, given trends in atmospheric CO2, CH4, halocarbons, etc. "cooling" is not likely to be a problem for the foreseeable future. In fact, if we burn enough coal over the next century or two, it's entirely possible that there will still be enough additional CO2 in the atmosphere 50,000 years from now to prevent the next glacial cycle (Archer 2009). Cooling is not going to be a problem. Heat, sea level rise, and especially alterations to the hydrologic cycle will be.
  4. Ned. You are saying that the CO2 is good since it will keep the next ice age off our backs? High sea levels (if slow enough) just means rebuilding on higher ground. Most commercial buildings last less than 30- years. Water is the ultimate recyclable commodity. We can manage water if we have enough energy. Solve the energy problem and food and water will be sufficient for all.
  5. Don't be silly. If we're able to alter the climate enough to prevent the next glacial cycle 50,000 years in advance by accident, I suspect our descendants will be able to come up with a way of dealing with the next glaciation whether it happens 50,000 or 130,000 years from now. 21st century climate change will mean real hardship for many people, primarily due to alterations of patterns of rainfall and drought, plus the impacts of sea level rise on poorer countries where "just rebuild on higher ground" isn't necessarily an option. (Who's going to offer to take in a few tens of millions of Bangladeshis?) I don't think it's reasonable to impose that kind of hardship on actual people living in this century while patting yourself on the back for "preventing" a very slow glacial advance 50,000 years in the future.
  6. How about preventing an ice age in the next 50 years? Or 100? 50,000 wasy our number. I think you are nit picking.
    Response: 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.
  7. There isn't going to be an ice age in the next 50 or 100 years. If that was your concern, then you can rest easy tonight. And tomorrow you can wake up and start working on the real problem, which is preventing the potential catastrophe caused by too much warming rather than too much cooling.
  8. Well that makes your climate models easy. Are you familiar with the phrase "Dead Certain." Warmer may be inconvenient. Ice will kill most of the life on the planet. I think we should plan for every possible future and not pick only the ones we want to "solve." By the way - how do I get the nam "N/A" and how do I change it? I am having some degree of trouble here.
  9. "If you're that concerned about an impending ice age," Really, I am not. My point is that it is possible warming will be good if it prevents an ice age. We seem to be in agreement that CO2 is preventing an ice age. We differ if the CO2 is good or bad. Butr I do not know. I only see it as an important question to answer and have yet to see a satisfactory answer.
  10. I hate to be reiterating an old point but its all about rate. The transition into and out of ice age is extremely slow by human terms. (around 10,000 years). The rate of warming we are creating is by comparison very fast. Rates of change that overwhelm species capacity to adapt are the danger. Also, an ice age hardly kills most of the life on the planet. We have been in and out of ice ages right through quaternary period. They affect temperate zones mostly.
  11. N/A writes: I do not know. I only see it as an important question to answer and have yet to see a satisfactory answer. Nothing wrong with that. Spend some time browsing through the pages on this site -- there is a lot of information, and a lot of very careful discussion of the current peer-reviewed literature. A number of the commenters here are scientists working either within climate science or in related fields ... they can provide a very valuable perspective, too.
  12. Thanks for the thoughtful responses. I hope you are right about an ice age being so slow. But it is probably the only factor that would justify an increase in CO2 at this time. My background is that I am a retired science librarian with an earned PhD. That should qualify me to do compreshesive searches of the current literature and to understand what I find. I do question those who want to divide comment into either "warmer" or "denier." And I do want us to consider many other questions other than "Is it getting warmer?" I think it is getting warmer. I wonder if that is good or bad. And I am not convinced that it is bad.
  13. N/A - perhaps you should start with AR4, WG2 on the IPCC website. It is heavily referenced and details the impacts. Check the references, decide for yourself. The critical question is how fast can we adapt? The problem areas as I see it are densely-populated delta regions (Bangladesh, Nile, Niger etc), and regions prone to long-lasting drought. Disruptions to water cycle are unfortunately not that easy to predict.
  14. Im glad you brought this up. I have heard argument in the area of the 'mini ice age'. The melting of the northern ice cap along with the melting of ice in Greenland to flood the northern sea with fresh water. The fresh water from the melting ice is lighter, and so tends to hug the surface, forcing the Gulf Stream lower and in the end, further east sooner. The bulk of heat from the Gulf Stream is left to transfer toward Europe then, as Canada finds itself cooling... and entering a miniature ice age whose duration is limited to centuries at most. Your comments on this general theory would be considered a rare light in an area I consider shadowed, and confusing at best. Im sorry for the lack of references. It has been many many years since I read of this odd theory and references are lost to time.
  15. OK. I have said enough and I still do not know why I am listed as "N/A" But I have one last thought. What are the circumstances that would make more CO2 good? How do we know they arr not in the future? Best to ask many questions and be ready for anything that happens. Have a Swiss army knife of solutions - not one solution for one problem and only that one solution. Warmer will be inconvenient. Ice will kill most of us - if not all. I am gary4books.
    Response: The N/A is a website glitch, still trying to figure it out.
  16. Scinan, I think you are talking about the North Atlantic Current portion of the thermohaline circulation. It has happened in the distant past, so reasonably it has been speculated to be a risk in the near future. More research has revealed that it is extremely unlikely to happen in the near future. More information can be found by clicking on the links in the "More Information" section at the bottom of the page by climatologist Stefan Rahmstorf, "The Day After Tomorrow: Some Comments on the Movie." (For the quickest route to the information, skip straight to the bottom of that page.)
  17. Scinan, I should clarify that the risk of a shutdown of the North Atlantic Current (thereby causing a Northern Hemisphere ice age) is not an ice age threat that is reduced by increased CO2. To the contrary, the threat is increased by increased CO2. The point of my previous comment was that the probability of it happening is very small.
  18. gary4books might be right. both sides of the argument seem to be afraid of the possibility of change. EVERYTHING CHANGES! The biology of this planet is good at adapting to changes. "Positives and negatives of global warming" is a ridiculously one-sided attempt of trying to purport to have a balanced view. (of course there are more papers on scary outcomes than on positive outcomes - no one funds/reads rosy pictures) Even with all the evidence in the world nothing is going to make energy companies let go of the status quo in time to make a difference, nor will it make enough people CHOOSE to pay more for energy. I believe all of us in the scientific community need to stop trying to WIN the argument and start working out what we know and what we still need to know - then we will actually be able to move forward intelligently.
  19. mginaus writes: The biology of this planet is good at adapting to changes. That's true, but that adaptation process involves lots of losses (e.g., lots of species go extinct during time of abrupt change). Just because "life as a whole" survived the K-T impact doesn't mean we as one particular species should welcome catastrophic climate change. In addition, we have a huge investment ("sunk costs") in technological and cultural infrastructure built around a relatively stable climate. Here in the US (where I live), a small but long-term change in patterns of precipitation could be hugely expensive, dwarfing the trivial costs of things like the Iraq war or health care. Look at economic impacts of the 1993 or 2008 Midwest floods, or of similar drought years. The West Coast would (will?) incur immense costs if snowpack in the Sierras declines and the regional water infrastructure has to be completely reworked. Etc, etc, etc. As for willingness to change, we're going to have to change anyway, due to the conflict between increasing demand and decreasing availability of oil in the coming decades. Nuclear would help but can't replace oil by itself, at least not in the near future. Switching back to coal will incur huge health and environmental costs, and if continued for the long term it would drive the climate into absolutely disastrous conditions. mginaus concludes: I believe all of us in the scientific community need to [...] start working out what we know and what we still need to know - then we will actually be able to move forward intelligently. Hear, hear! I agree with that, more or less. I'd just add that we know enough already to justify starting making changes now (actually, we should have started 20 years ago...) -- I think John Cook and all the others who contribute to this site have done a great job of summarizing what we do know and what we still need to figure out.
  20. I am 17 years old and home schooled doing a project on climate change (trying to find all aspects for and against climate change and their effects) so i am not a scientist and do not understand everything that has been talked about on this page so bear with my questions please. How do we know that decreased insolation due to the larger projections of increased ppm CO2 in the atmosphere (i.e. GTon C) doesn't outweigh the resulting reduction of outgoing radiation thus causing global cooling?
  21. Erin, We know because of the measurements. The Earth is retaining more energy than it is radiating back to space despite the decreased insolation. I recommend reading up on the net forcing. Likewise, if decreased insolation outweighed the forcing of CO2, then we would see a cooling trend as opposed to a warming trend. Look no further than our temperature records. As a high school teacher, I commend the level at which you are approaching this topic. Keep it up.
  22. Thank you chudiburg. So I have another question. If you look back on the 100k year cycles in figure 4 they all peak at about where we are now and that peak is sharp. Why does the projection for the natural cycle in figure 4 predict the same estimated high temperature for the next 50,000 years if that has not happened in the past (at least in that figure)?
  23. Question: In the projections shown in Figure 4, it looks like there is an upper limit of about 4 degrees C for the temperature anomaly, even at 5000 Gigatonnes CO2 emission, and only about 2 degrees for 1000 Gton. However, the graph in Figure 2 shows that the temperature anomaly is projected to reach 4 degrees C in just under 100 years, on a more or less exponential path, with no sign of slowing down. Is there or is there not an upper limit to the temperature anomaly given these assumptions about the magnitude of CO2 emissions? How sure can we be that the projections shown are correct, given the chaotic nature of the planet's climate? Question 2: Can climate change result in positive feedback as ocean warming leads to the release of more CO2?
  24. Erin, If you click on the link for the source of figure 4, the author of the article addresses this. It has to do with expected low insolation variability for the time being. It is worth noting that this agrees with some predictions, but disagrees with others. The primary thing to take away from the study is that if we continue to release large amounts of CO2, then we could potentially delay the onset of glaciation indefinitely. McCloud, the 5000 gigatonnes CO2 emission is based on an estimate of how much we could potentially release if we burn all available fossil fuels. Thus, with the calculated forcing of that much CO2, we see an upper limit of 4 degrees warming. This study may not be the best source for looking at future temperature anomalies, however, because its purpose is to look at the potential for preventing the next glaciation. The scope of the study really isn't to make precise temperature anomaly predictions, but rather predict how much glaciation will be delayed under different emission scenarios. I would suggest clicking on the link to the study. As for your second question, yes there is potential for a positive feedback here. As water warms, its capacity for storing CO2 decreases, which will eventually lead to the oceans actually releasing CO2 as opposed to taking it in. I am fairly sure that most climate projections take this into account already.
  25. I need to do more reading on Broecker on this, and I tend to be at odds with some of the literature. However, some of it has given me some hunches. The PETM was a period 55 million years ago with no glaciation. The popular media presented this as a possible future state due to greenhouse forcing. I believe this must be a complete error. Moran et al. presents Arctic Ocean sediment core data that argues for a transition period between glaciations during the same time (between 45 and 35 million years ago (Ma)) when the southern ocean Antarctic Circumpolar Current (ACC) was being formed. Their graphic describes before and after the ACC formation as "Greenhouse" and "Icehouse" climate states respectively. One estimate of that formation using neodymium isotope ratios by Scher et al. estimates the opening of the Drake Passage based on ocean mixing to be around 41Ma. Data such as Zachos et al. shows how northern glaciations occured at a time after a robust southern ice cap has been built up and maintained. I hold a MS in Physiology, and have only done some independent study in geology and audited a course in Earth's Climate History and completed one in Physical Oceanography. Long before this, being acquainted with climate swings, I drew an analogy between a mechanism in my field, the excitable membrane action potential conduction mechanism seen most robustly in nerve and muscle tissues to the climate system. In the action potential mechanism, there is a rectification reaction that occurs because sodium and potassium ions are set in opposing gradients accross the plasma membrane, and have selective channel proteins that conduct the two ions with differing time courses so that the fast response sodium causes a change in voltage in one direction called depolarization while the slower response potassium channels cause a voltage change in the opposite direction by virtue of the fact of their opposite gradient. I draw my analogy to the climate system in this manner: Temperature is an analogue for voltage, a greenhouse stimulus that occurs in the atomosphere is an analogue for the sodium response, and an oceanic/cryospheric rectification mechanism is analogous to the potassium response. I of course cannot deny orbital forcing mechanisms that occur on 40Ka, 100Ka, and I believe 20Ka range changes, as has been mentioned here, but I believe another very important part of the equation is the ability of the earth to respond to heating changes, which shows the contrast in response pre-ACC formation, the greenhouse earth, and post-ACC icehouse earth. The time course of cryospheric/oceanic response is on the order of multi-century to millenial, putting it an order of magnitude smaller than the orbital forcings. There is evidence in the fossil record of events that may corroborate this idea. Terms to look for are "Iceberg Armada," "Heinrich Events," "Younger (and Older) Dryas," as well as the "8200 year before present event." I have a while to go to fully quantify this idea, but since the ocean stores about 1000 times as much heat as the atmosphere, it is not absurd to envision the domination of the atmosphere by oceanic responses. It is conceivable that a threshold for the response will be crossed where greatly increased motility of global major glacial masses could lead to a reversal of a warming trend that would include a reversal of the ability of the ocean to absorb CO2. By far the lion's share of ocean is very cold, fed by yearly calving of glaciers at both poles leading to what is known as North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). These masses can represent a very adequate repository for resequestered CO2. I'm still in the "hunch" stage here, but I have posted some of my ideas at

Prev  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  Next

Post a Comment

Political, off-topic or ad hominem comments will be deleted. Comments Policy...

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

Link to this page

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us