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Climate change

  1. Oct 29, 2009 #1
    i saw a chart that showed that the temp has gone up single digit degrees every 100k years in a rapid manner and then followed by a downward ratcheting of temp into the levels where earth experiences an ice age. What is the dynamic that causes the temp drop after a rapid rise? Do we need a serious rise in temp to prevent the next ice age? Could we prevent an ice age by building a big coal fire (read co2 increase in the atmosphere here)? Not many people could survive an ice age.
     
  2. jcsd
  3. Oct 29, 2009 #2

    Xnn

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    http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter6.pdf

    Figure 6.3 of the attached link, illustrates temperature variations over the last 650,000 years.

    Temperature rises appear often, but not precisely at a fixed frequency (although it is on the time scale of 100,000 years).

    The temperature changes are synchronized with changes in the various greenhouse gases. There are also changes in the earths orbit that occur at a regular frequency (23K,26K,41K & 100 Kyear) thereby alternating the amont of solar energy received at various locations on the earth. However, notice that the temperature changes do not always follow these orbital changes. The key appears to be when greenhouse gases respond.

    The general thinking is that as the earth warms, increases in precipitation lead to greater sequestation of CO2 from the atmosphere, thereby resulting in lower temperatures. This is the dynamic that causes most of the temp drop after each rise.

    It's probably inevitable that another ice age will occur. Humans may try to prevent it, but after fossil fuels are depleted, there does not appear to be any economic way to maintain greenhouse gases.

    Right now, there is no chance of a ice age occuring since greenhouse gases are rising so much that the immediate concern is global warming. So, while it is probably inevitable that another ice age will occur, human civilization will be better off by limiting fossil fuel combustion to levels that could be sustained for a longer period of time.
     
  4. Oct 29, 2009 #3
     
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  5. Oct 29, 2009 #4

    Xnn

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    Excellant Point Skyhunter!

    Forgot all about CFCs.

    Are there any that don't destroy ozone too?
     
  6. Oct 29, 2009 #5

    mheslep

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    Apparently Hansen says a lot of things outside of peer reviewed journal papers. For instance, in 1988 he said the West Side Highway in NY city would be under water by now.

    http://dir.salon.com/books/int/2001/10/23/weather/index.html [Broken]
     
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  7. Oct 29, 2009 #6

    Xnn

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    Hansen Smansen; who said what doesn't really matter.

    http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf

    Table 2.1 on page 141 of the above link shows that CFC's are the 3rd greatest contributor to human caused global warming (after CO2 and CH4).

    Don't have a ready link, but some HFC 12 has a global warming potential 10,000 times that of CO2, while Sulfer Hexafluoride is over 20,000 times and these are not particularly expensive chemicals to manufacturer.

    So, if needed we could geo-engineer global warming without using significant amounts of fossil fuels. However, it'd be a very strange world if CO2 levels fell below a ppm. Most plants would fail to thrive, so there'd be global food shortage.
     
  8. Oct 29, 2009 #7

    sylas

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    The published research on projecting Milankovitch cycles indicates that even in the absence of any human influence, the Earth would not move into another ice age for many thousands of years. The interglacials, or periods of mild climate between ice ages, are of varying lengths, and the current interglacial, the Holocene, would under normal circumstances be expected to be a long one; comparable to the Stage 11 interglacial about 400 thousand years ago, due to a current low in the eccentricity of Earth's orbit. This would indicate the current interglacial would continue, in the absence of human influences, for as much as 50 thousand years more.

    References:

    This is based on the Milankovitch cycles and the orbital drivers for the ice ages. The primary cause of the long interglacial in the present is a low eccentricity of the orbit, which is continuing to reduce towards zero about 25 thousand years from now and a circular orbit. This cycle will reverse itself in time, and eccentricity of the orbit will increase one more.

    These cycles do not give enough direct forcing to drive ice ages; to move in and out of the ice ages it is necessary to include the effects of positive feedback such as temperature driven carbon dioxide levels and albedo from ice cover.

    An additional complicating factor, of course, is the human influence, which has shifted climate forcings well away from normal conditions of the Quaternary period and the cycles of glacials.

    The large increase in Earth's greenhouse effect that has occurred over the last century has brought the atmosphere rapidly to a state which has not been seen for millions years; well before the Quaternary and the cycles of glacials. There is no credible prospect of new ice ages under our immediate current conditions. On the other hand if industrial emissions of greenhouse gases ceases, then in time the atmosphere will gradually return towards a more "normal" composition.

    The long term impact basically depends on how much carbon is added to the atmosphere. So far we have added about 330 Gigatons. If nothing more is added, then the Earth's atmosphere could be expected to recover within the time span of the next expected glacial, which is still well into the future in any case, by the estimates cited above.

    If we continue adding more greenhouse gases, then there is a possibility of longer term changes beyond this time period.

    References:

    Human society is not used to thinking in scales of geological time. It's not clear whether human activities will result in a short term change in climate conditions for a a couple of centuries, or bring about a more lasting change for a some millenia, or even a completely new climate state. The differences between these possibilities are intriguing, but somewhat academic for economic or other "pragmatic" consequences to our current society.

    The bottom line is that there does not appear to be any reason to think a new ice is immanent, either with or without the changes seen over the last century.

    Cheers -- sylas
     
  9. Nov 1, 2009 #8
    http://www.snowballearth.org/could.html

     
  10. Nov 1, 2009 #9

    jambaugh

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    You'll have to be more quantitative to describe the phenomenon. Note that when looking for the beginning of an ice age you will pick the point where the temperature first starts dropping so it will necessarily follow a rise in temperature by definition. As to whether that rise is any steeper or dramatic than other random fluctuations you should first determine if such a phenomenon actually occurs before looking for the mechanism. Otherwise you're practicing a type of scientific sophistry...arguing toward a given conclusion rather than looking impartially at the evidence.

    Also beware the makers of charts. They may too be practicing such scientific sophistry.

    As far as preventing an ice-age goes I doubt we could with current industry. Possibly if we already have a permanent industrial base in space we could cook up some solar mirror type climate control but that's still science fiction. In spite of the current hype we still don't know enough about the climate to predict the effects of our actions in terms of instigating or preventing ice ages or global warming. Not to the degree to justify investing massive resources on a scheme we have a hunch might help.
     
  11. Nov 1, 2009 #10

    sylas

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    The basis for this is that given current solar input, there are several possible stable equilibrium conditions. Basically, if all the ocean could be frozen overnight, then the resulting planet would have a very high albedo, reflecting almost all the sunlight. Not enough energy would be absorbed to raise temperatures above freezing. There's no credible prospect of this happening; and it is not what happens in ice ages.

    More details at the page you are citing; and also in the text book Principles of Planetary Climate, by Ray Pierrehumbert, section 3.4.1.

    Cheers -- sylas
     
  12. Nov 2, 2009 #11
  13. Nov 2, 2009 #12

    sylas

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    You are referring here to research looking at questions about the extent of freezing in the snowball state; sometimes called the difference between "snowball" and "slushball". This remains an open research question about the nature of these extreme glaciations, rather than a question about melting and refreezing in a single proven model.

    In any case, there has been no "snowball"/"slushball" state for over 600 million years. Prior to that, yes, it is thought that the "snowball"/"slushball" melted and froze over again a couple of times, with the "snowball"/"slushball" state in place circa 2220 Ma ("Makganyene"), circa 710 Ma ("Sturtian") and circa 640 Ma ("Marinoan"). (See When did the snowball earths occur? for an informal description, and see Hoffman and Schrag (2002) The snowball Earth hypothesis: testing the limits of global change in Terra Nova, Vol 14, No. 3, 129–155 for a formal scientific reference.

    There is a fair amount of literature on the cases for and against the slushball (tropical terrestrial glaciation but with open water in equatorial oceans) and the hard snowball (ice over the tropical ocean as well) and both alternatives continue to be considered in the literature.

    Cheers -- sylas
     
    Last edited: Nov 3, 2009
  14. Nov 3, 2009 #13

    Xnn

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    Interesting links Sylas;

    Apparently, there is a huge gap of about 1.5 Billions years between the Makganyese and Sturtain periods when there is scant evidence of slush/snowball conditions.

    The Makganyese period occured 2.22 Billions years ago. Since then, the continents came have together into super continents and then broke apart numerous times. So, it's has to be very difficult to know exactly where land masses were that far back.

    As far as I know, there have been 3 named supercontinents.

    Rodina between 1100 to 750 Ma
    Pannotia between 600 to 540 Ma
    Pangaea between 250 to 175 Ma

    So, the 2nd slush/snowball period occured during the breakup period between Rodina and Pannotia; well before the Cambrian explosion 530 Ma.
     
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