Re: [asa] CO2 content

>
> Here's the "coincidence" that is being argued. PETM produces Azolla which
> sequesters a whole lot of CO2 which in turn causes cooling.
>

Azolla is an aquatic fern that floats on the surface of freshwater in warm
climates. There are actually two factors that allowed Azolla to sequester
lots of CO2 in the early Eocene. One is the globally warm temperatures.
However, the other was the existence of a gigantic lake otherwise known as
the Arctic Ocean. Land connections between Greenland and Europe, the Bering
land bridge, and the retreat of epicontinental seaways cut off the Arctic
from the rest of the oceans, allowing a freshwater layer to develop on the
top and making the deeper, salty parts relatively anoxic. This produced a
huge habitat for the fern and high levels of organic accumulation on the
seafloor. It's not a simple case of high temperatures automatically
producing lots of Azolla.

(Note: I have not gone back to the Azolla presentation to check the claims
about how much CO2 was sequestered, etc. I definitely wouldn't want to
assert that abundant Azolla is enough to cause a significant decrease in
CO2. My point is just that "warming causes lots of Azolla" is way too
simplistic.)

The end of the Eocene high temperatures and the Pliocene onset of glaciation
in the Northern Hemisphere are both closely tied to plate tectonic changes
that reorganized global ocean circulation and thus the weather and climate.
CO2 is certainly not the only driving factor.

No doubt some sort of new equilibrium temperature and CO2 level will be
reached, though it might be after humans squander the all the fossil fuel
and civilization collapses, along with the collapse of many ecosystems.
There are some negative feedback factors that may kick in and counteract
global warming, though there are positive feedback factors that aggravate
the existing warming trend, so there's no grounds for complacency in
assuming that the negative feedback will predominate. Again, this totally
misses the real problem, which is that the change is happening too fast for
organisms (including humans) to keep up, not that any particular equilibrium
temperature and CO2 level is better or worse.

 --
> Dr. David Campbell
> 425 Scientific Collections
> University of Alabama
> "I think of my happy condition, surrounded by acres of clams"
>

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Received on Tue Aug 26 17:20:06 2008