Calculations for CO2 Offsetting by Stoves
A 2007 study commissioned by Climate Care Ltd. quantified the amount of firewood required to cook family meals in Honduran homes with traditional stoves vs. TWP's improved cook stoves. Based on their reduction in firewood consumption, TWP were estimated to prevent the emission of an average of 1 ton* of carbon dioxide (CO2) per year per stove.

In 2000 David Pennise and Kirk Smith of the University of California at Berkeley conducted a pilot study of emissions from traditional "stoves" (3-stone open fires) vs. TWP stoves in Nicaragua. The emissions of CO2, carbon monoxide, methane, and non-methane hydrocarbons (NMHC) were measured in both types of stoves. The results showed a reduction of 0.282 tons of carbon emitted per year per TWP stove relative to traditional stoves. We converted this mass of carbon to the mass of CO2 (the standard for measuring fossil fuel emissions and by far the most abundant gas emitted from the stoves) by multiplying by 44 tons CO2/12 tons of carbon. This yielded a reduction of approximately 1 ton of CO2 per year per TWP stove.

Multiplying 1 ton of CO2 per year per stove by 7.5 years, the minimum lifespan of one properly maintained TWP stove, yields a total of 7.5 tons of CO2 that will be prevented from entering the atmosphere by the use of one of our stoves.

Reference
Climate Care Ltd., Ambiental PV, ENASA. 2007. "Kitchen Performance Testing, Tegucigalpa, Honduras and Managua, Nicaragua 2007."

Pennise, D.M. and K.R. Smith. 2000. "Greenhouse Gas Implications." In Ecological Woodstove Dissemination in the Pacific Region of Nicaragua to Reduce Greenhouse Gas Emissions. PROLEÑA Nicaragua, 19-26.

Calculations for CO2 Offsetting by Trees
We used data provided by the Ministry of Agriculture of El Salvador and Hidayat & Simpson (1994) to determine the specific gravity of wood from the six tree species TWP plants to offset CO2: Spanish cedar, mahogany, rosewood, mango, cashew, and Maya Nut. The average of the six species was 639 kg/cubic meter of wood. Our Guatemala Project Director estimated that these species have an average of 3.5 cubic meters of wood at maturity. Multiplying average specific gravity by average volume yields an average biomass of 2,237 kg per mature tree. Tree biomass is approximately 50% carbon, resulting in 1,118 kg or 1.118 tons of carbon per mature tree. Therefore approximately 0.9 mature trees offset 1 ton of carbon. Because trees may die before reaching maturity and because of potential sources of error in these calculations, we plant 5 tree seedlings to offset 1 ton of carbon.

Reference
Hidayat, Syarif and William T. Simpson. 1994. "Use of Green Moisture Content and Basic Specific Gravity to Group Tropical Woods for Kiln Drying." Research Note FPL-RN-0263. Madison, WI: USDA Forest Service Forest Products Lab.

Calculations for CO2 Emission Levels
We obtained the figure of 20 tons of CO2 emitted by the average North American by averaging the six references listed below. We used the four carbon calculators listed below to enter hypothetical parameters to come up with an estimate of CO2 emitted by each of the four lifestyle descriptions.

References
Coombes, Andrea. 2007. Turn Down the Heat. MarketWatch from DowJones.

Raich, Jim, Ricardo Bedoya, Eugenio Gonzalez, & Ann Russell. Biomass Production and Carbon Sequestration by Tropical Tree Species in Experimental Plantations in Humid Lowland Costa Rica. PowerPoint presentation. 

Union of Concerned Scientists. 2006. What’s Your Carbon Footprint? Greentips Environmental Ideas in Action.

CO2 Emissions by Country. Time for Change.

The World Bank. 2007. The Little Green Data Book 2007. Washington, D.C.: The World Bank. 

O’Neill, Meaghan & treehugger.com. 2006. Welcome to the Slate Green Challenge. Slate Magazine.

Carbon Calculators

www.carbonfund.org/site/pages/individual/category/
Carbon%20Calculators/

www.carbonify.com/carbon-calculator.htm

www.nature.org/initiatives/climatechange/calculator/

www.terrapass.com

* all tonnage figures are in metric tons. One metric ton = 2,200 lbs.