[Bored chemist]

A reduction of 50% from 21% would leave 10.5%, that's well into the range of "dizzy" according to that table and it would make it impossible to do anything. Even walking across the room would be impossible.


However, there's no sensible way we could see the oxygen levels drop by 50% so I don't understand why anyone is talking about it.
 
If we burned enough oil to use up 1 percentage point of the atmosphere (ie to go from about 21% to about 20%) then we would add about 1% of CO2 to the air.
2% CO2 in air is toxic to people.
That would certainly have serious effects on other organisms, and also on ourselves.
Very roughly, it would mean an increase in the CO2 by a factor of 25.
That, in turn would drop the pH of the oceans by about  log(25) i.e. about 1.4 pH units so the pH would shift from slightly alkaline to slightly acid.

Some things might cope with that, but the change, if it wasn't incredibly slow, would cause a lot of trouble.

[CliffordK]

I think there are many different calculations.

I was thinking of Mt. Everest which is supposed to have an atmospheric pressure of about 1/3 ATM, or the equivalent of 1/3 the oxygen.  People can tolerate the pressure as long as the changes aren't sudden.  The oxygen is too low for westerners, although the natives can get pretty high up without oxygen supplements.

I had read that CO₂ toxicity started at about 5% which is extremely high.  I have no doubt we will run out of coal, oil, and natural gas long before we reach that level.

What got us into this mess?
Is it the people?
"Big Oil"?
Governments?
Americans?

Perhaps that is the core of humanity.  We've never been content with living within our means.

When hunting became burdensome, we domesticated animals.
When grazing became burdensome, we started growing crops.
We've done what no other animal has done, growing our food, and selectively breading for yield and quality.

But... finally we've found ourselves using more energy than we can sustain.

It isn't cars or windmills or solar panels...  we just have too many people all requiring too much energy. 

[raven]

http://hermosabeach.patch.com/articles/dead-sea-lion-found-near-hermosa-beach-pier
Thought you might find this interesting. I read somewhere that there has been a 40% decline in Phytoplankton since 1950. When I read this article after the above to learn more
http://earthobservatory.nasa.gov/Features/Phytoplankton/page2.php
I became quite concerned considering the amount of marine deaths of late around the globe.
Just wondered what your thoughts were?

[yor_on]

Yep, there are some serious stuff going on. And you can backtrack it to the way we live and pollute. And then we have 'saviors' that reminds me more of fanatics than using common sense, wanting to fill the seas with tailored genes for cleaning it up. man-made organisms designed to pump out fuel and clean up waste. It's painfully obvious that some still believe Jules Verne to be fine and hearty. Also that 'Big Business' hope that this will let them make some real dough. All put together, with politicians that never hesitated to cut the Gordian knot, I'm sure we will see something like this soon enough. And when it backfire, as I expect it to do, those that did it will look at you and ask 'And what did you do ? Sat on your ass, didn't you. At least we tried.."

Well, fanatics has never won the day, of any kind.