Re: [asa] Global Warming

From: Rich Blinne <rich.blinne@gmail.com>
Date: Tue Jul 29 2008 - 12:37:22 EDT

On Tue, Jul 29, 2008 at 9:35 AM, j burg <hossradbourne@gmail.com> wrote:

>
> While I pretty much accept the IPCC findings and analysis, I am still
> a bit skeptical of the overall issue. Two reasons: (1) the amount of
> sunlight reaching the earth is, indeed, dependent on CO2 levels. But
> it is much more dependent on water vapor (cloud) levels.

The effects of clouds have been factored into the GCMs. See here:
http://www.iop.org/EJ/article/1748-9326/3/1/014001/erl8_1_014001.html

Also, satellite technology for measuring the effects of different types of
clouds is getting much better:

http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-6-3931

>
> (2) Soot levels also may play a part. If so, this could be an argument
> either way.
>
>
Soot does not equal aerosols, BTW. As a first-level explanation it holds but
rather it is the anthropogenic SO2 is what is the primary concern. Last year
there was a PNAS paper of how both the natural variability -- specifically
solar irradiation variability -- and anthropogenic variability played
together.

http://www.pnas.org/content/104/10/3713.full

What they did was to use cosmogenic Be-10 in ice cores as a proxy for solar
irradiation levels. The problem with Be-10 is how much to scale it so they
used three different scaling factors to see which fit the paleoclimatic
record the best. Beryllium 10 is like Carbon 14 in that solar irradiation
causes that isotope to be produced.

The forcings used in the model are shown here
http://www.pnas.org/content/104/10/3713/F1.large.jpg

The blue line is large scaling, the red medium, and the green small.

The results of plugging in the model is shown here:
http://www.pnas.org/content/104/10/3713/F3.large.jpg

Graph a is the current paleoclimatic reconstructions of the temperature
record which becomes the gray background in graph b. Graph b shows the
medium scaling of Be-10 is the best fit. What this shows is we have a good
grasp on what is causing the variability in the pre-industrial period
although one interesting finding of the paper is that even here solar
variability was less of a factor than volcanic eruptions. Graph c is during
the instrumental period. Note how if you don't include CO2 forcing and even
with large scaling you are 0.5 degrees C off. Yet again for the upteenth
billionth time, antropogenic climate change is shown even when both aerosols
and solar irradience differences are taken into account.

Rich Blinne
Member ASA

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Received on Tue Jul 29 12:37:42 2008

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