Re: It looks like the regression started to break-down in recent years...
Obviously you have neglected the methane gas released by all of those cows being raised for hamburger chains.
And do not neglect the effect of organized religion where all of those Hindu cows just walk until they drop, yielding neither shoes nor steaks.
Your graphs reflect the cliche that "figures don't lie; but liars sure figure."
This is NOT to suggest you are lying, merely than an ogive can be built to show any position by a clever statistician.
You guys are beating yourselves to death over a philisophical position of trying to interpret the world by empirical means--sorry, it can't adequately be done.
Publius