It is a well known fact that the true cause of global warming is the decrease of pirates operating on the high seas.
We see here that as the number of pirates decreased, the global temperature has increased. I now present some supporting evidence.
http://www.treehugger.com/files/2008/08/slow-freight-joins-slow-movement.php
As stated in the above article on freight by sailing ship:
Transportation by sail [...]
