DIYbanter - View Single Post - Global Warming

D Smith

(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?
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.

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

Re-phrase the question:

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

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.

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.)