Re: The oxygen levels on earth are shrinking, will we all just suffocate?

You have touched on several interesting issues in your question and I will 
try to respond to each of the individually.  First, however, it seems to me 
that what is really of interest to you is the the interaction of people 
with their environment and the possible problems caused by mismanaging that  
environment.  This is a VERY complex topic and I certainly don't have 
enough time to go into it here.  In your comments about the effect of 
deforestation on O2 concentration, however, you have demonstrated the basis 
of one of the disciplines used to study this topic that you may be 
interesting in researching further.  The study of elements and how they 
cycle through the hydro-, terra-, bio- and atmosphere is called 
biogeochemical cycling.  When you talk about oxygen and deforestation you 
are talking about the cycling of oxygen from the biosphere to the 
atmosphere (get it?).  I did a quick search under biogeochemistry and came 
up with several good sites.  A good place to start because of their copious 
links is the Global Change Research Information Office: 
 http://gcrio.ciesin.org/

Check it out and dive into the topic to your heart's content.  The site has 
links that are of interest to the laymen as well as the researcher.

Now, for your specific questions.  First let me say that I wouldn't be too 
worried yet, especially about the O2.  The concentration of oxygen in the 
atmosphere is greater than the human lung's capacity to remove it.  When 
you exhale, you release not only CO2 and N2 but a significant portion of 
the O2 you just breathed in.  Although the process is concentration driven 
(ie the higher the O2 concentration, the more readily O2 is absorbed into 
the blood stream) I don't believe that levels have gotten low 
enough to cause difficulty breating.  Secondly, O2 is a constantly 
renewable resource.  As long as there are plants living on this earth there 
will be production of O2 - and by plants I mean not only trees and grass 
and other terrestrial species, but also all the photosynthesizing aquatic 
organisms.  Often people don't realize what a HUGE part these creatures 
play in the global cycling of all the most important elements.  In fact, 
some scientists believe that deforestation in certain areas of the world 
and the resulting increases in CO2 will stimulate productivity in other 
areas of the world including the oceans (note: this is one theory of many 
and I want to be clear that I'm not trying to endorse one idea over 
another - frankly, I'm not an expert on this topic and can't give you a 
fair evaluation of all the current theories).

As for the ozone  and pollution issues, it is frankly hard to say.  Both 
of these issues and how to deal with them are not relegated to the field of 
science only.  Unfortunately (or fortunately?) one must also consider both 
politics and economics as well as the environment when talking about any 
such issues.  Is there a hole in the ozone layer?  Most definitely yes.  Is 
it a serious problem?  I'm not sure, it could be a huge problem that we 
might be able to fix.  The more me learn about it and the more we remediate 
our practices the more able to come up with solutions.  As for pollution, 
what do you consider pollution?  By some definitions, there it's a single 
place on this earth that isn't polluted to some degree.  That may sound 
scary but think about this - just your breathing could be considered 
pollution (you release CO2 after all).  I guess what I'm getting at is that 
there are no concrete answeres.  The world is an incredibly complex place.  
Should we be worried about our environment, are we irreversibly changing 
our environment for the worse?  I would say no to both.  I don't think we 
have gone so far as to ruin this planet for the future and while I would 
say don't 'worry' about it I would say be 'concerned'.  Keep informed about 
environmental issues and look at ALL sides of the problem - there is always 
more than one credible argument for any issue.  Educate yourself and make 
decisions appropriate to what you have learned and believe.  If everyone 
takes this responsibility I think we would be surprised at how fast we 
could solve of the most pressing issues of our time.