Arctic feedback

Discussion in 'Environment' started by Old Rocks, Apr 19, 2012.

  1. Old Rocks
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    Old Rocks Diamond Member

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    Abstract posted, full article at link.

    Permafrost carbon-climate feedbacks accelerate global warming

    Permafrost soils contain enormous amounts of organic carbon, which could act as a positive feedback to global climate change due to enhanced respiration rates with warming. We have used a terrestrial ecosystem model that includes permafrost carbon
    dynamics, inhibition of respiration in frozen soil layers, vertical mixing of soil carbon from surface to permafrost layers, and CH4 emissions from flooded areas, and which better matches new circumpolar inventories of soil carbon stocks, to explore the potential
    for carbon-climate feedbacks at high latitudes. Contrary to model results for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), when permafrost processes are included, terrestrial ecosystems north of 60°N could shift from being a sink to a source of CO2 by the end of the 21st century when forced by a Special Report on Emissions Scenarios (SRES) A2 climate change scenario. Between 1860 and 2100, the model response to combined CO2 fertilization and climate change changes from a sink of 68 Pg to a 27 þ −7 Pg sink to 4 þ −18 Pg source, depending on the processes and parameter values used. The integrated change in carbon due to climate change shifts from near zero, which is within the range of previous model estimates, to a climate-induced loss of carbon by ecosystems in the range of 25 þ −3 to 85þ −16 Pg C, depending on processes included in the model, with a best estimate of a 62 þ −7 Pg C loss. Methane emissions from high-latitude regions are calculated to increase from 34 Tg CH4∕y
    to 41–70 TgCH4∕y, with increases due to CO2 fertilization, permafrost thaw, and warming-induced increased CH4 flux densities partially offset by a reduction in wetland extent.
     
  2. CrusaderFrank
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    CrusaderFrank Diamond Member

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    Two words: Water vapor.
     
  3. Old Rocks
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    Old Rocks Diamond Member

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    Explaining how the water vapor greenhouse effect works

    When skeptics use this argument, they are trying to imply that an increase in CO2 isn't a major problem. If CO2 isn't as powerful as water vapor, which there's already a lot of, adding a little more CO2 couldn't be that bad, right? What this argument misses is the fact that water vapor creates what scientists call a 'positive feedback loop' in the atmosphere — making any temperature changes larger than they would be otherwise.

    How does this work? The amount of water vapor in the atmosphere exists in direct relation to the temperature. If you increase the temperature, more water evaporates and becomes vapor, and vice versa. So when something else causes a temperature increase (such as extra CO2 from fossil fuels), more water evaporates. Then, since water vapor is a greenhouse gas, this additional water vapor causes the temperature to go up even further—a positive feedback.

    How much does water vapor amplify CO2 warming? Studies show that water vapor feedback roughly doubles the amount of warming caused by CO2. So if there is a 1°C change caused by CO2, the water vapor will cause the temperature to go up another 1°C. When other feedback loops are included, the total warming from a potential 1°C change caused by CO2 is, in reality, as much as 3°C.

    The other factor to consider is that water is evaporated from the land and sea and falls as rain or snow all the time. Thus the amount held in the atmosphere as water vapour varies greatly in just hours and days as result of the prevailing weather in any location. So even though water vapour is the greatest greenhouse gas, it is relatively short-lived. On the other hand, CO2 is removed from the air by natural geological-scale processes and these take a long time to work. Consequently CO2 stays in our atmosphere for years and even centuries. A small additional amount has a much more long-term effect.


    So skeptics are right in saying that water vapor is the dominant greenhouse gas. What they don't mention is that the water vapor feedback loop actually makes temperature changes caused by CO2 even bigger.
     
  4. CrusaderFrank
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    CrusaderFrank Diamond Member

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    Clearly, CO2 sucks as a GHG compared to H2O. The Vostock cores clearly show CO2 as a laggard to temperature increase and not a cause. It's likely that something else, probably H2O was causing the increase (you can't measure increases in H2O from an ice core) and dragged CO2 along behind it.

    CO2, it's just not that powerful, especially in the almost imperceptible trace quantities we're dealing with today
     
  5. Old Rocks
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    Old Rocks Diamond Member

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    Climate myths: Ice cores show CO2 increases lag behind temperature rises, disproving the link to global warming - environment - 16 May 2007 - New Scientist

    So if orbital changes did cause the recent ice ages to come and go, there must also have been some kind of feedback effect that amplified the changes in temperatures they produced. Ice is one contender: as the great ice sheets that covered large areas of the planet during the ice ages melted, less of the Sun's energy would have been reflected back into space, accelerating the warming. But the melting of ice lags behind the beginning of interglacial periods by far more than the rises in CO2.

    Another feedback contender, suggested over a century ago, is CO2. In the past decade, detailed studies of ice cores have shown there is a remarkable correlation between CO2 levels and temperature over the past half million years (see Vostok ice cores show constant CO2 as temperatures fell).

    Rising together

    It takes about 5000 years for an ice age to end and, after the initial 800 year lag, temperature and CO2 concentrations in the atmosphere rise together for a further 4200 years.

    What seems to have happened at the end of the recent ice ages is that some factor - most probably orbital changes - caused a rise in temperature. This led to an increase in CO2, resulting in further warming that caused more CO2 to be released and so on: a positive feedback that amplified a small change in temperature. At some point, the shrinking of the ice sheets further amplified the warming.
     
  6. Old Rocks
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    Old Rocks Diamond Member

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  7. bripat9643
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    bripat9643 Diamond Member

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    If this were true, then the world should never have cooled after the MWP, but we all know that didn't happen.

    The problem with all these alarmist theories about run-away warming are the facts of history.

     
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  8. Old Rocks
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    Old Rocks Diamond Member

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    Now Pattycake, the CO2 level during the MWP was only about 280 ppm, and the CH4 level, about 700 ppt. Today, the CO2 is over 390 ppm and the CH4 is over 1800 ppt. And the MWP really wasn't all that warm.

    The Medieval Warm(ish) Period In Pictures

    Science marches on while skeptics don't

    The MWP was very unlike warming today; the growing North American glaciers during the MWP being somewhat of a giveaway. The MWP only affected warming in a handful of regions, with Greenland being especially warm (Figure 1), whereas much of the Earth was actually cooler than the late 20th century. By comparison; today virtually every glacier and ice sheet on the planet is in rapid retreat.

    Both the climate proxies and the climate models imply that the MWP was a re-organization of the Earth's climate, and that much of this re-organization can be explained by oceanic patterns of warming and cooling, although what started all this rolling in the first place is still unknown.
     
  9. CrusaderFrank
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    CrusaderFrank Diamond Member

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    If CO2 is such an awesome GHG how come you can never point to a single experiment where adding 200ppm does anything at all?

    You get null

    You get "time for new hypothesis"
     
  10. Old Rocks
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    Old Rocks Diamond Member

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    Come on now, dumb fuck Frankie, I did that in the 6th post. Because you haven't the mental ability to read real science articles doesn't mean that the rest of the world is that retarded.
     

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