Choose not having children (No sex). Use bicycles to commute 30 km to/from work. Spend more money on bicycles/rain gear/parts than it would cost to own/use car/car pool/public transport. Don't use heating in the winter and dress warmly instead. Don't use a clothing dryer and instead hang wash on rack to air dry. Do not believe in high-density residential planning because when things become difficult, those high-density dwellings will give everyone a taste of Iraq. Cannot afford to live close to work so have to use small very fuel efficient car to commute to work.