An alarmist statement

Excerpt from this letter:

I remember reading or hearing somewhere a few years ago (I can't retrieve the source) that if the people of China (pop. 1.3 billion) were to achieve the fossil fuel powered, electric toothbrush living standards of the USA (pop. 0.3 billion), within 50 years the Earth will be devoid of all oxygen-breathing life. (You don't need the source; the arithmetic proves the statement correct.)