Mulching your grass clippings over bagging has many advantages. The clippings are good for your lawn, it's faster to mow--reducing your emissions, and no plastic bags to bag the clippings. You could also dump them into a compost. The same can go for geting rid of leaves in the Fall.
Lawn tools with combustion engines have no emissions regulations like cars. Two stroke engines burn both gas AND oil! By minimizing your lawn care you can reduce your carbon footprint. There are electric versions of nearly every common gardening appliance. Just watch out for the power cord!