Despite the risk that commuting by bike might increase his longevity, Andy (far right) plans to stay in the saddle and keep up with the pack. Photo © Bill Lehmanowsky.
I like to ride my bike to work. With a round–trip distance of thirty–six hilly miles, I get the exercise necessary for my fifty–year–old body to compete with younger competitors during the summer road racing season. I can also feel good about my personal carbon budget as I reduce my auto use.
Or can I? Not according to University of Pennsylvania Business Professor Karl Ulrich. In his tongue–in–cheek analysis “The Environmental Paradox of Bicycling,” Ulrich calculates that the carbon savings from bike commuting are offset by the longer lifespan fit bicyclists enjoy. Bottom line, as an Ulrich protégé pointed out, “One of the single best things you can do for the planet is to limit your time here.”
But few people, no matter how much they care about the environment, are willing to do that intentionally. Instead, the idea of purchasing carbon credits has come into vogue. Everyone, from individuals to giant corporations, is jumping on the bandwagon in an attempt to reduce their carbon footprints. One offset project that is frequently mentioned is tree planting, under the theory that trees absorb carbon as they grow.
That’s true, and tree planting, like bike commuting, also has indisputable environmental health benefits, such as reducing erosion and providing wildlife habitat. However, planting forests has little, if any, long–term net effect on atmospheric carbon dioxide and global warming. And, unlike bicycle commuters, who don’t seek to sell their carbon savings to the neighborhood coal–fired power plant, timber companies are trying to profit in the carbon credit financial markets.
Proper accounting is the key to understanding why forests will not save our planet from profligate petroleum use. When a tree is planted it grows quickly above and belowground, absorbing carbon dioxide from the atmosphere to make cellulose and other plant building blocks. So far, so good—the growing tree is a carbon sink, storing more carbon than it releases to the atmosphere. But that’s not the end of the accounting.
Eventually, the tree dies. If it’s killed by fire, insects or disease, the tree’s stored carbon is returned to the atmosphere as it decays. If the tree is logged and put to commercial use, its stored carbon becomes carbon dioxide as soon as the wood product outlives its usefulness. Paper has a product life of about two years, while the wood used in houses may persist 100 years. At best, trees and wood products are short–term, not permanent, repositories of carbon.
On the other hand, carbon stored underground as oil, coal and natural gas is off–limits to the atmosphere.
It’s simply not part of the terrestrial–atmospheric global carbon cycle. That is, not until we pump it out of the ground to burn in our automobiles or power plants.
Exchanging carbon temporarily sequestered from the atmosphere in a forest for carbon pumped from the ground as oil or natural gas increases the amount of aboveground carbon, which increases the total amount of carbon in the atmosphere. Yet, in a nod to the political clout of the industrialized nations, that’s one of the offsets allowed by the Kyoto Protocol.
The bottom line is simple. There is no practical place to put the carbon produced from burning oil, coal and natural gas that will keep it from eventually increasing atmospheric carbon dioxide. Global climate change will only be lessened if we replace our use of belowground carbon with aboveground wind, solar and renewable energy sources.