He and his wife heat their modest home with wood, have only one car, and eat local food. They have changed every light bulb, installed solar hot water, and replaced every appliance with the most efficient one. These domestic practices cause them to emit about 50 pounds of CO2 a day, half of the average in the U.S. But those two plane trips emit as much each year as everything else in their lives.
Ahlfeld, a professor of civil engineering at UMass with a specialty in water and energy, spoke about carbon footprints at Saturday’s Amherst Farmers Market workshop.
This footprint metaphor originated 20 years ago with the publication of Our Ecological Footprint by Wackernagel and Rees, which gives a tool to analyze overall human use of ecological services (including land needed to produce our food, to produce wood and minerals, to regenerate oxygen and clean water, and to absorb our waste). Here are some tidbits Ahlfeld shared.
In 1900 the land area required to support the lifestyle of an average North American was 2 1/2 acres, and by 1995 it had risen to 10 acres. In 1900, there were about 14 acres per person of productive land on the planet, but in 1995 there were only about six acres available per person (due mostly to population growth). If everyone on the planet lived like an average North American, how many planets would we need? And are we willing to leave some space for other species?
Carbon footprints as a way to measure carbon emissions emerged about 10 years ago. Humanity, through the scientific community, has set targets for CO2 emissions that would probably keep planetary warming below 2 degrees Centigrade, the internationally agreed-on limit. The carbon footprint is an awareness tool that can help people take personal responsibility, and begin to answer the question “What can I do?”
Ahlfeld shared some more numbers. The biggest emitter nation now is China with 8.7 tons per year. The U.S. emits 5.5 billion tons per year. These numbers do not differentiate which portion of China’s emissions produce the cheap goods used by people in the U.S.
More telling is the per capita tons of CO2 emitted per year: In China it is 6.5, in the U.K. it is 7.9, in Germany 9.2, and in the U.S. 17.6. Meanwhile, in Afghanistan, the per capita tons per year is 0.3. Hmm, what is wrong with this picture?
Some other curious numbers came from How Bad Are Bananas? by Mike Berners-Lee. Bananas aren’t too bad because they travel by boat, grow under natural conditions and are sold with little packaging. Their footprint is about 80 grams of CO2 per banana. A basket of strawberries is 150 grams when they are local and in season (counting the use of fertilizer and hoop houses). Out-of-season strawberries are either flown in or grown in hothouses, so the footprint of a basket is 1,800 grams of CO2.
Reading this blog on a small laptop? Its carbon footprint is 200 kilograms of CO2 emissions to manufacture, 13 grams per hour to operate and 55 grams per hour for the use of the servers and networks.
Riding a bicycle a mile uses 65 grams if the cyclist is powered by bananas. If, however, that mile is pedaled by a person powered by cheeseburgers, the carbon footprint is 260 grams, about the same footprint per mile as two people driving in an efficient car.
And those plane trips to California? Ahlfeld said the carbon footprint of a person flying from point A to point B is about the same as driving the distance alone in a 25 mpg car.
To Ahlfeld, carbon footprints illuminate the personal moral question explored by Ramachandra Guha in his book How Much Should A Person Consume? Each human could be said to be entitled to a certain share of the planetary resources. Justice demands that we shouldn’t use more than our share. Ahlfeld concluded by saying that one of the great challenges of our time is to live with this reality.
A few more sources of information on carbon footprints: