The Top 10 green living myths

9. Green myth: Buy milk in paper or glass cartons if you have the choice. Fact: Because half-gallon plastic milk jugs use much less material, they have lower life-cycle greenhouse-gas emissions than glass or paper containers of the same size.

10. Green myth: Using your garbage disposal isn't good for the environment. Fact: It depends on a couple of local factors and also on what you would do with the garbage if you didn't put it in the disposal. If you're going to toss it in the trash, it's probably better to grind it up in the disposal, although the benefits may depend on how your community captures methane emissions from wastewater treatment and landfills. If you want to do it right, compost your leftover food.

I asked Hausfather to provide some scientific evidence for these claims and here they are:

1. Recycled versus virgin paper. This one is a bit thorny, he admits. He's willing to discuss it with me, so if you'd like to know more of what's behind the issue, say so in a comment and it can be a future blog post.

2. Local food is always green. This is based on a life-cycle analysis of food sources by Weber and Matthews (2008) in which they find:

"...the GHG emissions associated with food are dominated by the production phase, contributing 83% of the average U.S. household’s 8.1 t CO2e/yr footprint for food consumption. Transportation as a whole represents only 11% of life-cycle GHG emissions, and final delivery from producer to retail contributes only 4%. Different food groups exhibit a large range in GHG-intensity; on average, red meat is around 150% more GHG- intensive than chicken or fish. Thus, we suggest that dietary shift can be a more effective means of lowering an average household’s food-related climate footprint than “buying local.” Shifting less than one day per week’s worth of calories from red meat and dairy products to chicken, fish, eggs, or a vegetable-based diet achieves more GHG reduction than buying all locally sourced food."

Their paper is available here. Note that this is a rather carbon-myopic approach, and there are plenty of benefits to local food beyond their associated GHG reductions.

3. Dishwashers versus hand-washing dishes: This is based on calculations using dishwasher efficiencies from the US Federal Trade Commission and a study by the British nongovernmental organization Waterwise. Average dishwasher age is estimated to be seven years, based on the Waterwise study. The relationship between energy use per cycle and water use per cycle is based on calculations by the US Department of Energy. Average water use and temperature for handwashing (80 minutes and 80 liters per 12 place settings, 90F) is derived from the study by Bonn University, in Germany. Dishwasher capacity is assumed to be12 place settings. Whether dishwashing or hand-washing is optimal will differ based on the fuel mix of electricity generation, the water temperature used in hand-washing, the user’s water heater fuel and efficiency, the efficiency of the dishwasher, the temperature setting of the dishwasher, the load factor of the user’s dishwasher, and the flow rate of the user’s kitchen sink (which we assume to be 2.5 gallons per minute based on average sink flow data from the Laurence Berkeley National Labs). There is no clear winner, other than washing by hand with cold water.

4. Flying versus driving the car on vacation: The calculations are based on the carbon emissions per mile from flying via the World Resources Institute. Vehicle emissions per mile are based on the highway m.p.g. of the vehicle in question using the EPA’s fuel economy database and the number of passengers in the vehicle, taking into account the effect on fuel economy of extra passenger weight.

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