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Man Made vs. Natural Greenhouse Gas
Name: Mark
Status: other
Grade: 9-12
Location: 9-12
Country: N/A
Date: 5/31/2005
Question:
In all the discussions of global warming and pollution in
general, I don't believe I have ever seen any information on background,
natural sources for the green house gases and the various other
pollutants. How do the man made sources of pollution and green house
gases compare with the natural sources?
Replies:
Based upon what I remember having read in the Wall Street Journal (which has
published several op-ed articles by experts) man made greenhouse gases are a
very small fraction of the total. For example, water vapor is a greenhouse
gas. "Google" on "natural greenhouse gas".
Mike Loop
There is a lot of literature on "natural" vs. "anthroprogenic" climate
change and pollution. Once you tap into it you will find a lot of
disagreement with extremists on both fringes abandoning science and data
for posturing and dogma. For a start the report "Understanding Climate
Change Feedbacks" published by the National Research Council in 2003 will
give you some understanding of the complexity of the conflicting issues
with a fairly balanced point of view. The book "The Skeptical
Environmentalist" by Bjorn Lomborg provides a perspective tending toward
skepticism of the conventional wisdom of environmentalists. There are any
number of books that argue the conventional environmentalist perspective.
Both sides tend to commit logical fallacies to support their position
--
in lieu of actual data, which is amazingly scarce. Two contrary examples
suffice to illustrate my point. Global warming implies an increase in a
"global temperature", but what does that mean? Where I live the temperature
can range +/- 20 C. in less than a day, and changes by an even larger amount
with altitude, so what does a "global temperature" mean, and how is it
measured, and does it mean anything? On the other side some antagonists
argue that increasing agricultural productivity with chemicals improves the
environment by "freeing up" land for forests, wetlands etc. What is ignored
is that the "freed-up" land often goes to "suburban sprawl" and not returned
to pristine conditions.
If you do a literature review on the two journals "Nature" and "Science"
for the past 1-10 years you will find a wealth of data surrounding the
issues you wish to address. Both are prestigious, peer-reviewed journals so
they are about as close to a non-biased position as you are likely to find
on some very contentious issues.
Vince Calder
There is actually a great deal of naturally produced greenhouse gases in the
atmosphere. And that is a good thing, because without our protective
blanket of gases, we would fry during the day and freeze at
night. There is a
difference between the greenhouse effect (good) and global warming (faster
than
normal temperature change). Also, if you look at the records of climate
change over geologic time, we have obviously had very many changes in our
climate.
There is a cycle of ice ages that last approximately 100,000 years
followed
by a 10,000 year interglacial period. During the current interglacial
period, humans have been evolving and developing culture
and agriculture. So it
has been only relatively recently that humans have had a chance to alter the
global climate pattern. It has been 11,000 years since the last ice age
so we
are due for one. Scientific American had an article a few months ago that
hypothesized that humans have prevented a new ice age through their
agricultural practices. So, to answer your question. The atmosphere
does contain a
high concentration of carbon dioxide. But if you look at the trends in the
atmosphere through the geologic record you will see that the atmosphere
used to
contain a lot more, in fact it was one of the most prevalent gases in the
early atmosphere. Once life began and organisms started taking in carbon
the
amounts began to fall rapidly. Now the level of carbon dioxide is about
0.4%
of the atmosphere. However, before humans began adding more by burning
fossil
fuels, the level was 0.2%. So, since humans have been around, the level
has doubled. Is that enough to push global climate change to the levels
we see
now? Is it natural? Or is it a combination of both? Time will tell.
Van Hoeck
You bring up a very difficult and contentious issue: "natural" vs.
"anthroprogenic (caused by humans)" greenhouse gases. The answer is no one
really knows. The entire issue of global warming is hotly debated with
both sides often basing all sorts of consequences without the aid of
adequate data or climate models. If you can find the journals "Science"
and/or "Nature" in your school or public library you will find numerous
articles published every week. Everyone (almost) agrees that the level of
CO2 in the atmosphere has been increasing over the last century. However,
not everyone agrees that this is due to human activity, that it is
necessarily bad, or that it is significant. Some question that "global
temperature" is even a meaningful or useful term. That is: given the large
variations in temperature with longitude, latitude, altitude, geography,
etc. can a single "temperature" accurately measure what it is claimed to
measure.
Global warming is often "measured" by "proxy" effects. These include effects
like the pattern of tree rings, various isotope ratios in ice borings, and
many others. However, the relation of these proxy measurements and climate
depends upon some sort of model relating what is observed with global
thermal effects. There is a lot of disagreement over the reliability of
these models. There are a number of feedback mechanisms that determine both
weather (short term) and climate (long term). Some are the CO2 cycle, the
H2O cycle, particle and aerosol cycles, solar irradiance -- and those are
just a few of maybe a dozen. All of these cycles interact with one another.
In the recent past, some authors had predicted global disaster by the year
2000. It never occurred. That is not to say that the issues raised are not
valid, but the models were not able to take into account developments, both
in nature and in technology. The "green revolution" increased the efficiency
of agriculture. That was not envisioned in the 1960's. Fiber optics greatly
reduced the demand for copper. The invention of semiconductors made
computation far easier and faster than anyone even dreamed of 50 years ago.
I do not mean to belittle concern for the environment. The point is that if
we try to predict the future based on the past, the basis for prediction is
very uncertain, and one needs to be careful not to be too dogmatic about
what the future holds.
Your question is very good, but the answer is very uncertain.
Vince Calder
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Update: June 2012
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