I know I shouldn't feed the climate trolls but here we go for the millionth time:

Is Mars heating?
http://www.realclimate.org/index.php/archives/2005/10/global-warming-on-mars/

Is it the Sun?
http://www.sciencedaily.com/releases/2004/08/040803093903.htm

"So then, was it man-made global warming thousands of years ago?" No, it was a local fluctuation in temperature:
http://en.wikipedia.org/wiki/Medieval_Warm_Period

Keep up the good work, Neatorama

I think this is reason enough to worry about plastic bags.