“Another common recommendation is to turn lights off when you leave a room, but lighting accounts for only 3% of household energy use, so even if you used no lighting at all in your house you would save only a fraction of a metric ton of carbon emissions. Plastic bags have also been a major focus of concern, but even on very generous estimates, if you stopped using plastic bags entirely you'd cut out 10kg CO2eq per year, which is only 0.4% of your total emissions. Similarly, the focus on buying locally produced goods is overhyped: only 10% of the carbon footprint of food comes from transportation whereas 80% comes from production, so what type of food you buy is much more important than whether that food is produced locally or internationally. Cutting out red meat and dairy for one day a week achieves a greater reduction in your carbon footprint than buying entirely locally produced food. In fact, exactly the same food can sometimes have higher carbon footprint if it's locally grown than if it's imported: one study found that the carbon footprint from locally grown tomatoes in northern Europe was five times as great as the carbon footprint from tomatoes grown in Spain because the emissions generated by heating and lighting greenhouses dwarfed the emissions generated by transportation.”