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D Smith

(Doug Miller) writes:

In article , D Smith wrote:
(Doug Miller) writes:

In article , D Smith
wrote:

I am going to repeat some questions orignally posted a few weeks ago by
Bob Grumbine in another group. (He hosts the web site I referred to in
another post.) Please tell me which of the following points you disagree
with:

There is a greenhouse effect

Carbon dioxide is a greenhouse gas

Atmospheric concentration of carbon dioxide has increased over
the past 150 years

The source of that increase is human activity

Half credit on that one. The source of *part* of that increase is human
activity. Asserting that *all* of it is, is an article of faith, not science.

Pleased tell me what "part" you accept as being from human activity.
1%? 10%? 50%, 90%? 99%?

Second request, leaving lots of white space so it doesn't get missed.

Pleased tell me what "part" you accept as being from human activity.
1%? 10%? 50%, 90%? 99%?

Elementary physics shows that if concentration of greenhouse gases
increases, climate warms

*** That one, right there. ***

The causes of climate change are, at best, imperfectly understood, and to
argue that a *single* factor is "the" causative agent is to leave the realm of
science and enter that of speculation.

Read over the question again. Where do you get the idea that it says
that increasing greenhouse gases are the ONLY factor involved in climate?

That's implicit in the phrasing of the claim: "if concentration of greenhouse
gases increases, climate warms" completely ignores any other factors that
might act to cause the climate to cool.

You wish to interpret the question that way.

For the purposes of determining the effect of "greenhouse gases", is it
not traditional to try to isolate that component of the system? Isn't that
the way science works? Isolate a component, figure out its effect, then
build it back into the composite system?

The question is whether or not you agree that greenhouse gas
concentrations are ONE factor that affects climate (i.e., the response is
non-zero), and whether or not you agree that the effect is to increase
temperature when greenhouse gases go up (i.e., the slope of the
relationship is positive).

In an obvious exaggeration for the sake
of making the point, suppose that solar output were to diminish by fifty
percent at the same time that atmospheric CO2 levels were rising. Would you
still argue that "if concentration of greenhouse gases increases, climate
warms"?

I would argue that the increase in greenhouse gases will cause warming
that will offset some of the cooling caused by reduced solar insolation.

Do you *really* believe that increased greenhouse gases could offset a 50%
decrease in solar output?

Which part of "some" is so difficult for you to understand?

Or did you just miss it? Or did you just ignore it?

Look. I'm interested in trying to discuss this rationally. For you to
skip over my use of the word "some" makes it look like you want to argue
against a strawman rather than what I'm saying. I'm willing to accept
that you didn't mean to do that, but you're going to have to make a better
effort if you want me to continue to accept that. For that purpose, I am
willing to put some number on what I expect, so...

No, I can't forsee any increase in CO2 that would offset a 50%
reduction in solar output. That does not mean that CO2 does not have an
effect, though. For doubling of atmospheric CO2 (from 300-600 ppm), the
radiative effect (a positive forcing) would be roughly equivalent to
increasing the solar constant by about 23 W/m^2 (given current climate).
So, conversely, doubling CO2 would offset a reduction in solar output of
23 W/m^2 (about 1.7%). This would be a very large change in solar
constant, easily detectable by our space-based instruments. If the solar
constant DID change by this amount (in the absence of any change in
greenhouse gases, or "other external factors") then I would also expect a
change in global mean temperature somewhere in the range of 1-4C.

Now, are you willing to put some numbers on your estimates?

In the orignal question, there is an implicit "all other factors being
constant" in there.

Not at all. In the original assertion, there's an implicit "all other factors
don't matter" in there.

Let's go back to the original question:

Elementary physics shows that if concentration of greenhouse gases
increases, climate warms

The purpose of the sequence of questions is to isolate different parts
of the problem (call it "anthropogenic climate change", or whatever you
will). This is standard scientific method. Once we isolate a component, we
can examine its effect, and once we understand it we can look at it in
conjunction with all the other components again.

It is very difficult to assess the effects of "all factors" if we don't
know what any of them do individually. I am trying to find out what your
level of understanding is on several key components of climate theory.

Please note that this question says nothing about human effects - it
simply asks about "greenhouse gases" and global temperature (with a little
elementary physics qualifier thrown in).

Re-phrase the question:

"In the absense of other external factors causing off-setting
cooling...

That's better -- but it still assumes that you can know, and do know, what
*all* of those "other external [offsetting] factors" are.

When we eventually get back to the question of "what is happening to
our current climate?", then all those other factors DO come back in. But
at the moment, we are trying to isolate the role of one of those factors.
Does that make sense. Do you agree that isolating factors, for the purpose
of discussion and examiniation of effects, is a reasonable approach?

The global surface temperature record shows the last 20 years to have
been warmer than the previous 100.

There's another one. That isn't true: *ground*-based temperature monitors have
shown an increase due to increased urbanization, but *satellite* temperature
monitors show a slight decrease.

That is only true if you use the satellite record that ended in the
early 1990s (around the time Mount Pinatubo erupted, which caused a
pronounced cooling spike), and which also had errors due to such things as
satellite orbital decay, which introduced a negative trend bias. More
up-to-date satellite data and analyses confirm the warming trend.

Ummm.... no, that would be if you use current data....

Reference please? Most "satellite data shows cooling" sites only give
the information from Spencer and Christy's original work. I will try to
look up a reference, too. The IPCC 2001 assessment is getting rather dated
now (its graphs of satellite temperatures show warming), and I thought I
had some links to more recent things, but I'll need to dig a little more.

And attributing the ground-based record's warming to "urbanization" is
also a very weak case: analysis is done to reduce or eliminate an
urbanization effects in the record, and huge areas of the globe (northern
Canada comes to mind) show warming that is clearly not attributable to
"urbanization".

And even if it *were* true, it's still equally consistent with anthropogenic
and non-anthropogenic causes.

Please explain more fully. There are lots of other details that try to
distinguish between different sources of climate variation, but until I
know more about what you're thinking, I can't be sure what to say.

For example, as a first approximation global temperature rise could be
the result of changing greenhouse gases or solar output changes, but there
are subtle differences in the details that help distinguish between the
two. (There is also direct data showing that the output of the sun has not
changed significantly in the past 25 years or so, which is the easiest way
do eliminate solar output as the cause of the current warming.)

The point is that even if it is getting warmer, the temperature increase in
and of itself is proof only of a temperature increase -- not of what caused
it.

And that is the purpose of trying to isolate components of the system,
and examining eveidence that supports or eliminates a variety of causes.
For example, an argument that "the sun is doing it" is not very strong in
the presence of direct measurements of solar output that do not show an
increase in the past 20 years.