4 billion sounds about right, maybe a little high. I got 3.6 billion, based on US population and some local counts of one round per week per 200-400 people in nice weather. So, maybe 2 billion to account for winter, then add back in some for Europe. I'll go with 3 billion.
I can't wait until the end of the year to find out the real number!
Somebody is out there counting, right?
3 billion implies about 100 throws per second. If each throw stays in the air for 4 seconds,at any given time there are 400 discs in the air (not counting field work). I read somewhere that there are 1,200 to 1,400 golf balls in flight at any given moment. So, the proportions seem about right.