The relation between the plastic bag using and the Global Warming is the more you use the plastic bags, the more Carbon dioxide has been let into the atmosphere of the world. This gas comes from the burning in the production processes. When you have more plastic bags, you have to burn them more and this causes the consequent pollution problems.
The plastic bag is the cause of the Global Warming. It needs 450 years for its decay. It you burn it, there is hydro-carbon compound which causes the pollution problems and Global Warming. If you use the cloth bag, it will reduce the contamination of carcinogen. If everybody changes to use the cloth bag only one day a week, it will reduce over 100 million plastic bags per year.