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A 2nd ice age?

  1. Feb 12, 2010 #1
    How long ago was the last ice age? Does an ice age pose any threats to species on Earth? If there were a 2nd ice age, would humanity survive it?
  2. jcsd
  3. Feb 12, 2010 #2
    Depends on the geologic definition. Most put it at 11,400 years BP. Every estimate I have seen is falls into the 10,000 to 14,000 years BP range. Some would argue that we are in an ice age that began millions of years ago, and cycles between glacial and interglacial epochs.

    Any disruption of the environment poses a threat to some species, yet affords opportunities for others.

    They survived the previous glacial periods, no reason to suspect they would not survive another.
  4. Feb 12, 2010 #3
    We are still in an ice age -- look at the poles, is there ice there?. The last glacial maximum was about 20,000 years ago -- that was when there was a lot a lot of ice on the poles. That wasn't the first ice age in earth history however, there have been many many many ice ages before, that's because the earth is old.
  5. Feb 13, 2010 #4

    We are currently in the interglacial period of an Ice Epoch. The planet has cooled to the point it is starting to oscillate between extreme cold (glacial period) and cold (interglacial period).

    The planet has been cooling for the last 10 million years.

    As the planet cooled, the first ice sheets that formed where in the Antarctic. As the planet cooled further ice sheets started to form in the Northern Hemisphere.

    There is now a sever glacial/interglacial cycle where massive ice sheets form in the Northern Hemisphere which cools the entire planet by around 4C. For 3 million to 800,000 years the cycle was 41 kry. The cycle is now roughly 100 kyr.

    The interglacial period is short, roughly 12kyr to 15 kyr. The glacial period is long roughly 90 kyr. A 2 mile thick ice sheet covers Canada, the Northern US states, and Northern Europe during the glacial phase.

    When the planet is colder it is drier. Almost a third of the Amazon rain forest was converted to savanna during the last glacial cycle. There is a massive increase in dust from large deserts that form during the glacial phase (extreme cold) that is deposited on the polar ice sheets.

    Humans would likely survive another glacial cycle. The planet could not however likely support 6.5 billion to 10 billion humans during a glacial cycle. During the last glacial cycle, humans almost went extinct however at that time there was not technology to help address the problems.

    This paper has a graph that shows the glacial/interglacial cycle over the last 3 million years.

    The 41 kyr world: Milankovitch’s other unsolved mystery by Maureen E. Raymo et al.

    http://rsai.geography.ohio-state.edu/courses/G820.01/WI05 climate history/2002PA000791.pdf

    Last edited: Feb 13, 2010
  6. Feb 13, 2010 #5
    As noted above humans where near extinction 70 kyr ago due to droughts that lasted thousands of years. At that time the total human population on the planet was reduced to around 2000 which is close to the limit to maintain genetic diversity.

    The thousand year drought periods are cyclic and are caused by something that abruptly cools the planet. There is a 10 fold increase in atmospheric dust (as compared to current interglacial conditions) deposited onto the Greenland ice sheet during the abrupt cooling periods. Some of the dust comes from the Sahara desert that expands when the planet is colder.


    This is the paper that this summary is referring.

    Features of Evolution and Expansion of Modern Humans, Inferred from Genomewide Microsatellite Markers

  7. Feb 21, 2010 #6
    Interesting! I had believed that the reduction of human population approximately 70 Kyr ago was due to the Toba eruption (short term), rather than the periodic fluctuation in climate conditions (long term). Maybe you could clarify this.

  8. Feb 22, 2010 #7
    False. The planet has been cooling for the past 4.5 billion years as radioactive elements have become increasingly scarce due to short half-life isotopes (i.e. H3) and by various tectonic processes that work to remove heat from the earth's core.

    False. The first known glacial deposits and ice sheets are in Africa approximately where the Sahara desert is now because it used to be at the south pole.

    Also, i think it is important to distinguish between the climate and the planet because you seem to mixing it up.

    It is also interesting to note, in my opinion, the theoretical consequences of the snowball earth (circa 0.8 ga). I don't know if i buy the theory myself, but if true it provides an interesting story of how resilient life can be and how much it will flurish when given the chance.
  9. Feb 22, 2010 #8


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    You are speaking at cross purposes. The temperature of the core has very little to do with the temperature of the surface. What is happening with radioactive elements is pretty much irrelevant to the surface, which is what Saul was talking about.

    Cheers -- sylas
  10. Feb 22, 2010 #9
    Sylas, that is just wrong. Take the following image for example:

    Surface radiation accounts for the plurality of energy in our atmosphere and is directly related to subsurface thermal processes. If it wasn't for radiative decay of elements in the mantle and core (and perhaps i should have included the mantle in my previous statement) this would be a barren planet without any mountain building as we know it. This heat flux from the earth's interior is actually the mechanism that broke down the "snowball earth" which lead to the explosion of life in the Cambrian.
    Last edited: Feb 22, 2010
  11. Feb 22, 2010 #10


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    Energy from inside the Earth does not figure in that diagram anywhere. All the surface radiation is accounted for by the energy coming in from the Sun. Just add up the numbers.

    You are awfully mixed up there. The mountain building is true enough, because this comes from plate tectonics, which is driven from inside the Earth. But you are incorrect about snowball earth. Melting of snowball earth has nothing to do with geothermal heat fluxes. In the snowball earth model, the melting of the snowball occurs from a build up of carbon dioxide, which comes from geological processes. But what counts from the interior is the carbon, that traps heat from the Sun. The actual heat that melts snowball earth is surface heat driven by the Sun. Geothermal heat has no role at all in melting snowball earth.

    Note that we are straying close to topics which mentors have unfortunately decided that they cannot handle at present. But geothermal energy should be on topic just fine.

    The geothermal energy flux works out to a bit less than 0.05 W/m2. It is far too small to show up in the diagram you are using, which is all about climate and surface temperature -- all of which is related to how energy from the Sun is distributed.

    Cheers -- sylas
  12. Feb 22, 2010 #11
    Perhaps I am missing something, but the incoming radiation is 341, 161 making its way into the earth, and the surface radiation is 356. That gives you a 195 W/m2 gap. When considering the thermal energy regularly released in volcanic activity, faulting, and other processes it would be hard to imagine that not playing a role in climate. There is an ongoing debate , however, among geomorphologists about climate forcing tectonics or tectonics forcing climate.

    These geologic processes you elude to are constrained primarily by their thermal state, so it is therefore inaccurate to claim geothermal heat fluxes have "nothing to do" with carbon fluxes.

    Where did you get that number from?
  13. Feb 22, 2010 #12


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    You are indeed missing something. In that diagram, you can add draw a horizontal line and add up fluxes inwards and outward at different levels. Don't forget the 333 flow energy down to the surface from the atmosphere as backradiation. Also, there's 17+80 flowing up as convection and latent heat.

    The numbers don't quite balance due to some rounding errors, but there's no role whatever for heat from inside the Earth. It's too small to matter. In fact, that diagram indicates a slight excess of heat energy flowing DOWN, into the ocean. The reasons for this are beyond the scope of this thread; in the paper from which that diagram is taken, this is associated with increasing temperature of the ocean in the current climate, due to heat coming in from above.

    I think you are mistaken about the debates with geomorphologists. No-one thinks climate is forcing tectonics, as far as I know. The impact of tectonics on climate is subject to debate, but the impact is almost entirely from the consequences of how continents and mountains are arranged, which in turn impacts ocean currents and air flows. There is no significant role for heat from within the Earth for climate; and I do not think this is part of any scientific debate.

    Thermal state BELOW THE SURFACE. I didn't say geothermal heat fluxes have nothing to do with carbon fluxes. I said they have nothing to do with heating of the surface. Surface temperature of the Earth is all about how energy from the Sun is distributed; it has nothing to do with heat from the core of the Earth.

    In this case, I looked quickly at wikipedia. However, let's note that the number is not really known precisely. You can find a range of estimates. You tell me... what do YOU think is the total energy flux from inside the Earth up to the surface?

    Here, for example, is First measurements of Earth's core radioactivity (New Scientist, 27 July 2005 by Celeste Biever) reporting on Experimental investigation of geologically produced antineutrinos with KamLAND in Nature Vol 436, pp 499-503 (28 July 2005). This was very interesting work using neutrino detection to make inferences about Earth's internal heat sources.

    The Nature paper abstract says the total heat dissipation from inside the Earth is about 32 TeraWatts. That works out to about 0.06 W/m2. So suggesting less than 0.05 may have been too small. Say less than 0.1 W/m2. It is negligible for surface temperatures, but it is of course the main determinant for Earth's internal temperatures, below the surface.

    Cheers -- sylas

    Added in edit. Thanks for asking for my source, by the way! Wikipedia in this case was a bit out, and given without a proper reference. I have now edited the wikipedia page Earth's energy budget to give a better number for the geothermal flux, with an adequate properly published reference, albeit rather dated. I've given geothermal flux in the wikipedia page as 44.2 W/m2, based on Pollack, H.N.; S. J. Hurter, and J. R. Johnson (1993), "Heat Flow from the Earth's Interior: Analysis of the Global Data Set", Rev. Geophys. 30 (3): 267–280. But if someone has a better reference, let me know! It's a useful reminder to be careful using wikipedia... but wikipedia can benefit from using us!
    Last edited: Feb 22, 2010
  14. Feb 22, 2010 #13
    That heat flow sounds more reasonable to me. I should know more about this since I am going to defend my Masters in Thermal Geophysics later this spring, but I must admit I know little about how that translates into climate processes... perhaps another of my short comings considering i attend the College of Oceanic and Atmospheric Sciences.

    As far as my comment to geomorphology, see the following paper:
    Landscape response to tectonic forcing: Digital elevation model analysis of stream profiles in the Mendocino triple junction region, northern California
    Noah P. Snyder et. al.


    Whipple 1999, Journal of Geophysical Research.

    There is a more authoritative one by Molnar and England, who lead this field of science, but I can't remember what it is right now. I thought the idea of climate forcing tectonics was absurd when I first heard it in my geomorphology class last fall but it is surprisingly difficult to resolve the issue.

    thank you.
  15. Feb 22, 2010 #14


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    Best of luck with your defense!

    Unfortunately, current climate is such a "hot" topic that mentors don't really want us to discuss it. I'm hoping we'll sort it out better in time, but for now, climate is off limits, sadly.

    But the geothermal fluxes are fine. Since my last post I also found a more recent paper: Earth's surface heat flux by Davies and Davies (2009) which proposes 47 +/- 2 TW, or about 0.09 W/m2. It's not actually an easy number to measure, but all the numbers we've quoted have been in this ball park.

    If you could indicate a good reference that gives the current conventional view of total geothermal fluxes, that would be great.

    Sure... but these are all cases where, as I suggested previously, the influence is because of the change to the physical arrangement of the surface, and not because of the actual heat input. The impact of mountains and basins and continents and so on for air flow and ocean currents is very significant, and this is the major way in which tectonics has an implication for climate.... that is, geomorphology. There is also important influences from geochemical processes impacting composition of the atmosphere or reflectance of the surface. But actual internal heat? It is a drop in the bucket by comparison.

    Sometime if and when the whole climate matter is managed better, the associations of geomorphology and chemical impacts would be well worth looking at, for consequences over the very long term for Earth's climate.

    Cheers -- sylas
  16. Feb 28, 2010 #15
    Amazing such a low number for population. What about the Toba Super eruption?
  17. Mar 5, 2010 #16
    I decided to jump in on this thread because I searched it for the word Holocene and it did not come up. Once you understand the Holocene you will be well on your way to putting "A 2nd ice age?" into perspective.

    The Holocene is simply our current warm interval (interglacial) between 'ice ages' (glacials).

    The Holocene is the uptick on the right hand side of the Ice Core Graphs Note the horizontal dotted line (Freezing Point). These warm interglacials like the Holocene are very brief compared to the 'ice age' glacials.

    Here is a close up view of the Holocene . Again the present day is on the right. I won't take sides in the global warming v. global cooling debate, but the Holocene graph certainly has many examples of both phenomenon.

    That last interglacial, 125,000 years ago, was called the Eemian. The Eemian was way hotter than today's Holocene.

    The 'ice age' between the Eemian and the Holocene lasted about 90,000 years, and the ice covered Canada, 1/2 the USA, Great Britain, and most of Eastern and Western Europe. The ice was almost a mile thick. Then the massive warming of the Holocene started, and sea levels surged upward well over 300 feet. . It was surely a crappy time if you were a caveman living in a beach-camp.

    Here is a really fascinating graph based on ocean sediment cores which allow us to understand climate history going back several hundred million years. Again the present day is on the right.

    You can call it "Mother Nature" or "Hand of God" but either way these climate history graphs are fascinating stuff.

    The bottom line on the question of "a second ice age" is this: The second ice age (glacial period) happened millions of years ago.

    Sorry for the bigger sized type, but I'm visually challenged.


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