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Originally Posted by Essay
I think the oceans and lands are about equivalent in CO2 cycling abilities; with most of the oceans being a "desert" for life--coastal waters being the main productive areas.
...and the oceans remained mostly as a constant in equation of CO2 balance--until the industrial age. I was focusing on the land-based contribution to CO2 balance as the factor being strongly influenced by civilization; with the Amazon being a prime example.
Being the fastest growing forests, they may have drawn down the most CO2 after the American civilizations collapsed.
It's something like 100 billion tons of carbon dioxide exchanged by the lands each year. If globally, or even regionally at various times through history, we shifted that balance by just 2-3 billion tons/year, then climate could be influenced over the course of decades or longer--assuming CO2 does act as a fine-tuning thermostat. After a large collapse the shift could be 5-10 billion tons/year, for decades or even a century or longer.
The point of this thread seems to be that globally there was a large collapse in many civilizations around 1500--the transition between the MWP & LIA--especially the intensively agrarian New World civilizations that seem to have cultivated two continents.
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Originally Posted by engineerdude
I find this collapse of civilizations around 1500 intriguing as well - but I seriously doubt it has anything to do with CO2. Perhaps there is something that both causes large-scale disruptions and also causes a change in CO2 levels, but I do not see how the Amazon can have anything to do with it, at least not directly.
To explain, look at this:
total biomass of all land plants: 1.25 billion tons
total biomass of blue-green algae in oceans: 44 billion tons
Far from being a "desert" of life, the oceans contain 97.2% of all the plant life on our planet, by mass. I said "most" of the oceans are deserted, but your percentage must still be wrong (uncitable?).
The blue-green algae (cyanobacteria) are what gave us our current atmosphere starting 2.8 billion years ago, and they continue, through sheer volume, to say what happens in our air.
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Well, yes; those numbers sound about right--as far as I know--but you need to include "the rest of the story" as Paul Harvey used to say.
For the oceans there are also the higher life forms, fish and mammals--comprising a billion tons or so--that grow on that 44 billion tons of plankton.
Total fish biomass in worlds oceans estimated to be 2 billion tonnes
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Similarly on land, there are those "1.25 billion tons [of] land plants" that you mention, which are supported by
the terrestrial microbiome.
Over 1500 billion tons of biomass fills our terrestrial biome--in our soils. So compared to your 44 gigatons of plankton, I think our soils are more significant (
do you still think it's 97% in the oceans?).
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Originally Posted by University of Alaska
http://picea.sel.uaf.edu/manuscripts...obbierep97.pdf
For contemporary climate and an atmospheric C02 concentration of 312.5 ppmv, TEM [Terrestrial Ecosystem Model] estimates global carbon storage of 1781.4 x 10^15 gC (Pg C). This estimate does not include the carbon content of inert soil organic matter.
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It is our agricultural practices, cultivation and harvesting regimes, and land use/land cover changes which affect the largest carbon pool.
I agree that the microbes control our atmosphere, but that is my point--just look what we've done to the soils of this planet through the process of civilization--desertification, deforestation, and denitrification.
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p.s. (1 PgC = 1 GtC) one petagram = one gigaton (billion tons)
