Re: Sun expanding?

Message ID: 860040711.Es

Dear Kenneth:

Based on the phrasing of your question, I'm going to assume that you are a K-3 instructor rather
than a K-3 student! Therefore, I'm going to pitch this on about the same level as you worded your
question. If this causes any problems, just let me know.

First, let's define our terms here. The greenhouse effect (GHE) is a mechanism for trapping infra-red
radiation within the atmosphere. It is one possible source of global warming. Global warming is a
climatic change in which the average global temperature rises over time and it may indirectly be
associated with increased UV radiation at the Earth's surface and ozone depletion in the
stratospheric ozone layer.

The GHE isn't really directly causing any of these things. The GHE is causing the absorption of
infra-red radiation in the atmosphere -- a process that you can observe by comparing the low
overnight temperature on a cloudy versus a clear night. Without this absorption, the average Earth
temperature would be so cold it would be almost uninhabitable (-18C vs. 15C). Therefore you
might not want to say that ozone depletion, global warming and increased UV are all being attributed
to the GHE. All of these things are instead attributed (and perhaps attributable) to changes in
atmospheric composition -- messing with the chemistry of the air that we breathe and that regulates
atmospheric processes -- that is, increasing greenhouse gas emissions. And some of these gases
(for example, CFC's) do more than just contribute to the GHE, they also deplete ozone.

Our atmosphere certainly experiences natural, long-term global warming and cooling over intervals
of decades, centuries, millennia -- well, you get the idea. However, the global warming being
speculated and debated about today is not natural but rather anthropogenic -- resulting from human
activities. Whether or not global warming is actually occurring, whether it is natural or
anthropogenic, whether it would result in more negative effects or more positive effects overall --
these are all being debated and probably will not be resolved anytime soon. However, I personally
believe that, based on some of the proposed outcomes, society might want to seriously consider
terminating this global-scale, atmospheric experiment.

Now to your first comment/question. I am not an astronomer, but I do know that solar
aging/expansion is a VERY long-term process and its effects would be climatically significant only
on a time-scale consisting of millions of years. So I think we can discount that in relation to more
short-term effects such as the global warming episode currently being debated.

In other words, solar expansion will not affect climate significantly over the span of multiple future
generations, but rather over the time span of multiple species, and in the case of humans, over the
span of multiple civilizations. In my mind, well before we see the effects of solar expansion, we will
either be long gone or evolved well beyond our present form. We have a lot more to worry about
from asteroid impacts than solar expansion -- and an asteroid impact's affects on climate would be
rapid and catastrophic!

On to your other questions/comments. Danger of intense UV radiation is the major byproduct of
ozone depletion. Please note that ozone depletion and global warming are not directly related.
Global warming (if it is occurring and is sustained) may play a role in ozone depletion, but the
science of this role is not yet well understood. From what I can gather, warming of the troposphere
(the lowest 8 - 12 miles of the atmosphere, where our weather occurs) may cause cooling of the
stratosphere and this could lead to more ozone depletion. However, there are other processes that
may balance this depletion, and this may not, in fact, occur anyway. If it does occur, and there are
no balancing processes (processes that will either decrease ozone destruction or increase ozone
production) then we will experience increased UV radiation and several related effects (e.g.
increased skin cancer, suppressed immune systems, decreased agricultural production, etc.)

I hope this helps. Your goal was unclear from your question, but I assume you were brainstorming
and came up with an alternative hypothesis for these problems. I commend your efforts. Over the
long-term, solar expansion may indeed cause global warming, ozone depletion, and increased UV,
but I doubt that you would find consensus on that statement among all atmospheric scientists. I also
doubt that it has been given much consideration since it will probably happen too far in the future to
affect humankind. Atmospheric scientists tend to be a practical-minded bunch.

If you have any further questions on this topic, you can contact me at the e-mail address below.

Clay Harris
Middle Tennessee State University
e-mail: cdharris@frank.mtsu.edu