Here's an Old Favorite

WHICH CAME FIRST THE CHICKEN OR THE EGG?

http://www.lavoisier.com.au/articles/greenhouse-science/solar-cycles/IanwilsonForum2008.pdf

http://www.barnsley.towntalk.co.uk/eventsimg/barnsley22124.gif

http://www.londonstimes.us/toons/cartoons/joel_chicken_or_egg.gif

In case you are still not sure what the 
mysterious external factor is at the 
end of my Lavoisier Society 
power-point presentation, 
it's the long-term lunar tides!!

[And I thought my last PP slide would be a dead giveaway!]