Guardian puts it in perspective

Yes, they are ugly, wasteful and deadly to turtles.  But their contribution to climate change is miniscule.  The average Brit uses 134 plastic bags a year, resulting in just two kilos of the typical 11 tonnes of carbon dioxide he or she will emit in a year.  That is one five thousandth of their overall climate impact.

George Marshall

The Guardian, Thursday September 13 2007