The focus here is not global warming - please read closely:
According to study conducted by scientists from the Scripps Institute there is less oxygen in the atmosphere today than there used to be. The study is based from data dating back to 1989 from all over the world.
The 20 year study concluded that, as carbon dioxide accumulates in the atmosphere, available oxygen is decreasing. Three oxygen molecules are lost in our atmosphere for each carbon dioxide molecule that is produced.
Ice core data shows a 30% increase in carbon dioxide since the beginning of the industrial age which would amount to an increased loss of 90% oxygen in the atmosphere if the math is correct.
It's clear no matter how you look at it that oxygen depletion is a very serious issue - from dead zones in the ocean to a reduced amount of oxygen in the atmosphere.