[LMB] CO2 - Re: Butter Bugs! Well, almost.... OT:
paal at gis.net
Fri Jun 27 04:20:19 BST 2008
----- Original Message -----
From: "Mark Allums" <mark at allums.com>
To: "Discussion of the works of Lois McMaster Bujold."
<lois-bujold at lists.herald.co.uk>
Sent: Thursday, June 26, 2008 9:02 PM
Subject: Re: [LMB] CO2 - Re: Butter Bugs! Well, almost.... OT:
> Greg Hennessy wrote:
>> On Thu, Jun 26, 2008 at 2:53 PM, Mark Allums <mark at allums.com> wrote:
>>> There is something that a lot of people overlook. CO2 is not really a
>>> greenhouse gas, Al Gore notwithstanding. The main greenhouse gas is
>>> water vapor, with methane running a distant second.
>> What does it mean to be "not really" a greenhouse gas?
>> Does it mean you argue it isn't, but when challenged
>> you concede it is one?
> I have read, and I believe, and I will look up a reference if necessary,
> that CO2 is responsible for about 2% of warming, and water vapor, about
> 95%. Methane, fluorocarbons, and other things, the other 3%.
- begin quote of Covey email --
Dear Prof. Battisti,
Part of my job here at LLNL is to accurately communicate the results of
my work to scientific colleagues and the public. Accordingly, you
should feel free to share the comments below.
Page 11 of the brief begins, "As shown below, computer models predicting
future warming must overestimate warming, because they generally use an
incorrect increase in carbon dioxide concentration of 1% per year." It
is not true that models "generally use" this rate of increase. Model
simulations of 20th century global warming typically use actual observed
amounts of atmospheric carbon dioxide, together with other human (for
example chloroflorocarbons or CFCs) and natural (solar brightness
variations, volcanic eruptions, .) climate-forcing factors. Model
simulations of future global warming use analogous input; of course it
is not possible to observe the future, so a variety of scenarios
involving possible atmospheric concentrations of carbon dioxide, etc.,
are employed. These range from stabilization of atmospheric carbon
dioxide at twice its pre-industrial value by the end of this century
(IPCC SRES B1) to continuously increasing atmospheric carbon dioxide at
the rate of a bit less than 1% per year (IPCC SRES A2). Each climate
model simulating the future is run several times, with several different
scenarios. All of this has been standard practice in climate modeling
for the past ten years.
Pages 11-12 quote my 2003 review paper correctly regarding idealized
simulations in which atmospheric carbon dioxide is assumed to increase
at the precise rate of 1% per year. Note that in the end of the quoted
passage, I say that this rate of increase could "perhaps" be considered
realistic "as an extreme case in which the world accelerates its
consumption of fossil fuels while reducing its production of
anthropogenic aerosols." I'm no expert on scenarios, but from what I
hear about China and India I wonder if the world is already on that
track. In any case, the purpose of the 1%-per-year scenarios is to
compare different models' responses to identical input - not to produce
realistic possibilities of future climate. For the latter purpose,
climate model output from the IPCC SRES B1, A2 and other scenarios has
been widely used for several years and has been publicly available for
over two years on my group's Web site at
Finally it is not true, as implied on Page 12, that "sole reliance on
models to the exclusion of observed behavior" is the basis of future
climate prediction. As noted above, modern climate models are used to
retrospectively simulate the 20th century as well. Simulation of 20th
century global warming is an important confidence-builder for climate
models. Indeed, the observed warming during the 20th century cannot be
explained other than by assuming that the models are reasonably accurate
in their response to greenhouse gases. This point was clearly made by
the IPCC report published in 2001. Pages 12-13 ignore all this and
instead use "a constant-rate warming" of 1.8 degrees C per century
"based on actual observations." A constant-rate (i.e. straight-line) [*]
extrapolation of global warming from the 20th to the 21st century, as in
the brief's Figure 2, is a favorite technique of one of the authors, Pat
Michaels. This technique gives 21st century warming at the low end of
the spectrum of possibilities resulting from the different model-input
scenarios. It is one possible future, but it's never been clear to me
(or to anyone else I know besides Pat) why the other possibilities -
all of which involve more global warming - should be ignored.
What Curt was indicating I expect is that a straight line extrapolation is
a bad model/extrapolation to use--China, India, etc., have been increasing
their output of COx nd NOx and such, so using a straight line approximation,
results in considerable underestimates.
Note--I saw Curt last year at a dormfloor reunion, I've known him since my
freshman year of college...
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