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%?


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.

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?

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.

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.


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....
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.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.