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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.

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Climate Hustle

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)

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. 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.

Basic rebuttal written by Anne-Marie Blackburn


Update August 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

 

Last updated on 7 August 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Further reading

Tamino discusses predictions of future solar activity in Solar Cycle 24.

Acknowledgements

Many thanks to Sami Solanki for his invaluable advice and feedback as well as John Cross for his very helpful comments.

Comments

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Comments 351 to 366 out of 366:

  1. @jhnplmr:

    Please note that posting comments here at SkS is a privilege, not a right. This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter.

  2. JH: Fair enough.

    jhnplmr: I have replied on a more appropriate thread.

    Response:

    [JH] Thank you.

  3. "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?

    Response:

    [JH] Lose the snark or lose your posting privileges. No more warnings.

  4. #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.

  5. #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.

  6. 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.

  7. 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.

    Insolation changes at the end of the 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.

  8. 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.

  9. How is Figure 4 determined?

    (-snip-).

    Response:

    [DB] Figure 4 is based directly on Figure 3 from Archer 2005.

    Sloganeering and arguments from personal incredulity snipped.

  10. 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

  11. Climate Dialogue has a good and recent overview of the potential effect of a new Maunder Minimum, in its "Introduction" to that topic.

  12. Will somebody please add to the Further Reading section of this post, a link to Ari's bibliography of readings on future glaciation?

  13. 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.

    Response:

    [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.

  14. Echo_Alpha @363, evidence please.  Or are you only interested in sloganeering?

  15. Echo_Alpha...  Then if it's a fact you should be able to show us the research that supports that position.

  16. 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?

    Response:

    [TD] Read the text. Then click the Intermediate tab and read that text.

     

  17. 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. 

    Response:

    [JH] Sloganeering snipped.

  18. 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.)

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