GLUMAC - Engineers for a sustainable future

Natasha Houldson, P.E., Portland Mechanical Engineer

In Issue #6 of "Sustainability Matters," Sonya Salanti and Albert Sitorus described carbon emissions, carbon offsets, and ways in which Glumac supports the reduction of carbon emissions. How can we put that all into perspective?

A Few Statistics

Worldwide, the average carbon dioxide emissions per capita are about 6 tons per year. In the U.S., the per capita average is much higher, around 20 tons per year. Of those 20 tons, about 12 tons come from commercial and industrial sources. The remaining 8 tons come directly from individual energy usage, namely transportation and home energy use. That means that individual energy usage in the U.S. is higher than the 6-ton average encompassing personal, commercial and industrial uses worldwide! That fact alone should make Americans consider our personal energy usage habits.

Transportation

What do typical transportation activities produce? Using one gallon of gasoline in your car produces about 20 pounds of carbon dioxide emissions directly, or 26 pounds if you account for upstream processing of the fuel. As for airline travel, each passenger on a commercial flight produces an average of 0.6 pounds of carbon dioxide per mile flown. That’s 600 pounds of carbon dioxide emissions per passenger on a 1000-mile flight!

Home Energy Use

For home energy use, carbon dioxide emissions vary widely from state-to-state and from day-to-day. The national average is about 1.3 pounds of carbon dioxide for every kilowatt-hour of electricity used in your home. For an average home, that results in about 15,000 pounds of carbon dioxide emissions per year for electricity. In Oregon, use of hydroelectric power and other factors result in a much lower average – about 0.3 pounds of carbon dioxide per kilowatt-hour used. However, that still adds up to 3000 pounds of carbon dioxide emissions per household per year for electricity.

Trees and Carbon Sequestering

The "Sustainability Matters," Issue #6 article on carbon emissions described the concept of "carbon offsets" – projects that compensate for carbon dioxide emissions from one source by avoiding an equal amount of pollution elsewhere, or by sequestering carbon. "Sequestering" simply refers to the inherent removal of carbon dioxide from the atmosphere as trees or other plants grow, absorbing carbon in the plant material itself.

How much carbon can be sequestered in trees? Dry wood contains about 50% carbon by weight, and each pound of dry wood is the equivalent of about 2 pounds of carbon dioxide gas removed from the atmosphere. A softwood tree one foot in diameter may contain up to 500 pounds of carbon, equivalent to removing about 2000 pounds of carbon dioxide from the atmosphere. A large sugar maple tree can remove up to 450 pounds of carbon dioxide from the atmosphere each year! The USDA estimates that all forests in the U.S. sequestered about 300 million tons of carbon per year from 1952 to 1992 – equivalent to 25% of U.S. carbon dioxide emissions during that time period.

Conclusions