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How we know an ice age isn't just around the corner

Posted on 1 September 2010 by Anne-Marie Blackburn

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

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

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

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

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

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

This post is the Basic version (written by Anne-Marie Blackburn) of the skeptic argument "We're heading into an ice age".

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Comments 51 to 69 out of 69:

  1. scaddenp at 14:25 PM, I am looking for some explanation as to why it would not be so. Only about half of the current emissions are estimated to remain in the atmosphere, so the other half are being absorbed by natural processes which indicates that those processes are not that slow. In addition the seasonal fluctuations indicate that the capacity to absorb extra CO2 are in excess of the total anthropogenic emissions and further indicates that natural processes may have the capability of being a number of times faster.
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  2. johnd, you would need evidence that in the absence of human emissions of CO2 natural processes would be removing 2ppm CO2. Before the Industrial Revolution, the system was more or less at equilibrium - natural processes weren't removing more CO2 than they were emitting. They are now only removing half of the additional CO2 humans are emitting, i.e. the CO2 which has disrupted the equilibrium. So why would you think that CO2 would be removed at similar rate without human emissions? CO2 levels don't just drop for no reason - they are usually a feedback process.
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  3. JohnD, You know what the natural processes are that remove CO2 from the atmosphere. You even commented on it. As the post makes clear, ocean uptake of CO2 has profound consequences of its own; natural processes are not necessarily benign. Nor is it guaranteed to continue as it has done in the past
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  4. GC @ 48 - "I see plenty of evidence to suggest that CO2 is not a major climate driver." I gotta disagree GC, the link between CO2 and global temperature goes back a long way. The last 400,000 years. 650, 000 years. 800,000 years. However if yours is a version of the CO2 lags temperature argument, see here Why does CO2 lag temperature? And it's only a forcing this time around, not a feedback, because of human greenhouse gas emissions.
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  5. Anne-Marie Blackburn at 19:20 PM, I agree, CO2 don't drop for no reason. Just as the seasonal variation doesn't vary for no reason either. The nett global variation is greater than the total estimated human emissions, and when measured regionally the annual variations can be up to about 50ppm, but more often around 20ppm, well in excess of human emission levels, so the capacity to absorb higher levels is available if the right conditions are in place. These variations whilst large by comparison to the human emissions are small compared to the total land and ocean emissions which are about 27 times human emissions. Thus only a very small variation in the natural processes is required to make a significant difference to the nett gain or loss of CO2 from the atmosphere.
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  6. johnd, I still don't see the relevance of your point. Natural factors would probably have led to cooling. Yet global temperatures are increasing, most probably because of increased greenhouse gas concentrations. The rate of removal of these additional greenhouse gas emissions or seasonal variations in CO2 levels do not change the fact that an ice age is unlikely. Nor does the capacity to remove additional CO2. The analysis is based on past and current observations, not hypothetical scenarios.
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  7. Daniel Bailey (#50), The link you site assumes that CO2 concentration in the atmosphere drives global temperature whereas the exact opposite is more plausible. Looking back hundreds of millions of years we still lack the time resolution to put this matter to rest once and for all. It seems likely that what is true for the last 700,000 years is also true for the earlier Ice Ages. See my response to Dapplewater.
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  8. Dapplewater (#54), Thanks to much improved time resolution, the Vostok ice core studies convincingly demonstrate that temperatures lead atmospheric CO2 concentrations. It is nonsense to suggest that CO2 is driving global temperatures over the periods of time covered by the ices cores. However, the hypothesis that falling global temperatures are associated with increasing glaciation, falling sea levels, reduced precipitation, widespread arid conditions and falling CO2 concentrations looks plausible.
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  9. GC @ 58 - "it is nonsense to suggest that CO2 is driving global temperatures over the periods of time covered by the ices cores." I agree with you. Cavemen, woolly mammoths and sabre tooth tigers did not drive SUV's and build industrial smokestacks. Given the limits of scientific certainty that is. No, back then, CO2 acted as a feedback, responding to the temperature change, caused by changes in the Earth's orbit -out gassing from the oceans as the Earth warmed thereby amplifying the warming effect, then being absorbed back into the oceans as the Earth cooled. This was all in the "argument" I referred you to earlier.
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  10. Anne Marie, An ice age isn't just around the corner because we are still in an ice age. I'm sure you know that we are in the Quaternary Glaciation that started 2.58 million yrs ago. That's why we still have ice sheets in Antarctica and Greenland. Despite recent global warming, temp. today is one of the coldest in 600 million yrs. For most of geologic history, earth's temp. was above 17C.
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  11. Dr. Doom It is worth bearing in mind that SkS is a site designed for communicating science to the general public. It is therefore reasonable to use the term "ice age" in its colloqial sense, rather than as its strict geological jargon meaning. There is a fine line between precision and pedantry, and it is important to consider the intended audience. Anne Maries' title is perfectly reasonable.
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  12. DrD#60: "today is one of the coldest in 600 million yrs." How is that relevant to today - and how is it relevant to this thread? See the estimating sensitivity from paleoclimate thread More in general, it enhances your credibility when you provide a source for such statements.
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  13. From Dr Doom: Despite recent global warming, temp. today is one of the coldest in 600 million yrs. For most of geologic history, earth's temp. was above 17C. I will here echo muoncounter and suggest a citation is in order. Royer et al 2004 suggests that there was a period, centered around 300 Ma in the past, where global temperatures were lower than those of the present. But I will again echo muoncounter and suggest that your comment quoted above has little to do with whether climate science contrarians are correct in suggesting a new glacial period is imminent (or that one has been fortuitously forestalled by AGW).
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  14. Gentlemen, I'm sure Ms. Anne is perfectly reasonable. When communicating science to the public, it's important to be precise to avoid misunderstanding. The relevance of pointing out that today's temp. is one of the coldest in 600 million yrs is simply to support the fact that we are still in an ice age. It is relevant to this tread since we are talking about ice age today or in the near future. The source is the journal Physics & Society Vol. 37 No. 3. Temperature reconstruction by C.R. Scotese and CO2 reconstruction by R.A. Berner.
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    Response:

    [DB] Pedantry is not particularly becoming.  But since that is the sole point of this comment, I must point out that we are in an interglacial period within said ice age.  Given the CO2 we are injecting without sign of letup, some literature suggests we have already averted the next glacial phase; another 700 Gt or so will avert the next 5 glacial phases.  Google it if curious.

    Let's move the dialogue back to matters of substance, please.

  15. Doom#64: "Physics & Society Vol. 37 No. 3. " Interesting source. You select a graphic (seen more frequently from the famous geocraft.com website) buried within an article with the following preamble: This article has not undergone any scientific peer review. Its conclusions are in disagreement with the overwhelming opinion of the world scientific community. The Council of the American Physical Society disagrees with this article's conclusions. Author: Christopher Monckton of Brenchley That's why we like to see sources for such sweeping statements. Did you happen to note the lead article in the same volume? The abstract: In this paper, we have used several basic atmospheric–physics models to show that additional carbon dioxide will warm the surface of Earth. We also show that observed solar variations cannot account for observed global temperature increase.
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  16. Actually, I'd like to invite Dr. Doom to discuss the relevance of his assertion. It must have relevance, because s/he took the time to write it. I'm not going to immediately dismiss him as an agent provocateur, but after spending over a year on this site, I can understand the overwhelming desire to do so.
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  17. DSL#66: "I'm not going to immediately dismiss him" I don't dismiss the person; I dismiss the source for the assertion - as did the APS when they printed Monckton's piece of work.
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  18. Agreed, Muon, but I still want Dr. Doom's stated opinion on the matter, particularly in light of your comment.
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  19. Dr Doom: What does the Scotese paleo-temperature reconstruction have to do with claims that a glacial period is imminent (or has been fortuitously forestalled by CO2 emissions)? It is claims such as those that this Skeptical Science article is meant to rebut.
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    Moderator Response: [Dikran Marsupial] I suspect Dr Doom is still promulgating the fact that according to strict geological usage we are still in an ice age at the moment (as the Earth has permanent ice caps). However it has already been pointed out to him that the colloqial use of "ice age" is appropriate for this article as it is for communication of science to the general public, who use "ice age" to mean a time of substantially greater glaciation than we see today. Dr Doom has made his point, while it is factually correct, it is not of great importance to the discussion. Thus there is no need to discuss it any further, I suggest we take Dr Doom's caveat as read and go back to the substantive scientific issues.

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