On Sun, Sep 16, 2012 at 1:44 AM, meekerdb <meeke...@verizon.net> wrote:

> In fact it [CO2] has been less than half the current level during the
> last 600 thousand years

There have been at least 4 times in the last 600 thousand years when the
CO2 levels were nearly as high as they are now. And the link between CO2
and temperature is far from clear. During the late Ordovician period 450
million years ago there was a huge amount of CO2 in the atmosphere, about
4400 ppm verses 380 today, and yet the world was in the grip of a severe
ice age. During the last 600 million years the atmosphere has almost always
had far more CO2 than now, abut 3000 ppm on average. The only exception was
a period that lasted from 315 million years ago to 270 where there was
about the same amount of CO2 as we have now. The temperature was about the
same then as it is now too, and during the late Ordovician that I mentioned
before it was much colder, but other than a few very brief ice ages during
the last few million years the temperature has always been warmer than now.

> But it is not just the level that is worrisome, it is the rapidity of
> increase, which would appear as instantaneous on the paleoclimate studies.

If you adjust the scale of a graph you can always make a gentle rise look
like a near vertical wall.

 >> And I think people sometimes forget that CO2 is not the most important
>> greenhouse gas, water vapor is
> But water vapor equilibrates with ocean temperature very quickly, whereas
> CO2 takes hundreds of years to come into equilibrium.  Water vapor is the
> most important green house gas, but it acts as a positive feedback,
> amplifying other warming (or cooling) effects.

If water always produced positive feedback then with all the water on this
planet life would never have existed in the first place, but things are
more complicated than that. Let me ask you something, if the world's
temperature increases will that create more clouds or fewer clouds? It's a
very simple question with profound consequences because clouds regulate the
amount of solar energy that runs the entire climate show. Increased
temperature means more water evaporates from the sea, but it also means the
atmosphere can hold more water before it is forced to form clouds. So who
wins this tug of war? Nobody knows, its too complicated. Water vapor is a
far more powerful greenhouse gas than CO2 and unlike CO2 it undergoes phase
changes at earthly temperatures, it can be a solid a liquid or a gas which
makes it much more complicated than CO2 which is always just a gas, at
least on this planet.

And then there is the important issue of global dimming, the world may be
getting warmer but it is also getting dimmer. For reasons that are not
clearly understood but may be related to clouds, at any given temperature
it takes longer now for water to evaporate than it did 50 years ago.

  John K Clark

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