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What is carbon footprint?

Just like walking in the sand leaves a footprint, we leave a carbon footprint. Our everyday choices involve direct and indirect use of carbon. Your carbon footprint accounts for the total amount of carbon produced by of all activities you engage in. Sometimes connecting everyday activities to carbon production is straightforward; fossil fuels used to make gasoline to run a car is one example we are familiar with. But the production of most products we use, clothing we wear, and food that we eat, also leave a carbon footprint, and these impacts are more complicated to track.

The term carbon footprint represents all the different gases that contribute to global warming. 

Greenhouse Gases

Green House Gases (CO2­, CH4, & N2O) occur naturally in the Earth’s atmosphere, but human activities are increasing the levels.  Concentrations of greenhouse gases in the atmosphere vary, each greenhouse gas can stay in the atmosphere for a distinct period (referred to as residual time), and can absorb different amounts of heat. Because the concentration, residual time, and heating capacity are different for each greenhouse gas, it is difficult to assess their collective impact on the environment and make comparisons.

The Global Warming Potential of green house gases indicates the amount of warming a gas causes over a given period (usually 100 years). Global Warming Potential is an index; CO2 has an index value of 1. Standard ratios are used to convert the various gases into equivalent amounts of CO2.

The Global Warming Potential for all other Green House Gases is the number of times more warming they cause in comparison to CO2


Greenhouse gases absorb energy in the atmosphere and re-radiate it, causing air temperatures to warm.



The Food for Thought app is focused on the carbon footprint of food, and the impact our food choices have on the climate.

How do you measure a Carbon Footprint?

Carbon Dioxide equivalent

The CO2-e, or carbon dioxide equivalent, is a recognized measure that allows you to express the impact of different greenhouse gases as a common unit.  For any quantity and type of greenhouse gas, CO2­-e signifies the amount of CO2­ which would have the equivalent global warming impact. A quantity of green house gases can be expressed as CO2­-e by multiplying the amount of green house gases by its global warming potential.

In terms of the carbon impact of food, the total climate change impact of all the greenhouse gases caused by food production, from farm to fork, can be represented by one number.

Why do Carbon Footprints Matter?

Center for Sustainable Systems

University of Michigan's

Greenhouse Gases Factsheet

Since the Industrial Revolution began around 1750, human activities have contributed to climate change by upsetting the carbon balance and adding more CO2 and other greenhouse gases to the atmosphere. Burning of fossil fuels involved with power production, industry, and travel, as well as the clearing of agricultural land (deforestation) and its management for crop and livestock production, have contributed to increased greenhouse gas emissions and a climate that is warming at an unprecedented rate.

The carbon footprint for an average U.S. household is approximately 150 pounds of carbon dioxide equivalence (CO2-e) per day, or 48 tons CO2-e a year. (Jones and Karmmen, 2011).  To put this in context, the American carbon footprint is twice the European average and nearly five times the global average.


The U.S. represents less than 5% of the world’s total population but was responsible for 14% of total human-generated GHG emissions in 2015, according to an EPA report.

Red meat (beef, pork, and lamb) and dairy production together account for nearly half of the greenhouse gas emissions associated with producing, processing, distributing, and selling food in the U.S. (Weber and Mathews, 2008)

Learn More! 

Calculate your Carbon Footprint

Global Footprint Network

How many planets does it take to support your lifestyle? Take this quiz to find out your Ecological Footprint, discover your biggest areas of resource consumption, and learn what you can do to tread more lightly on the Earth.

The Nature Conservacy

Estimate your personal or household greenhouse gas emissions with this online calculator, analyze your footprint, and learn about what you can do to take action. 

Environmental Protection Agency 

The calculator estimates your footprint in three areas: home energy, transportation and waste. Everyone's carbon footprint is different depending on their location, habits, and personal choices.

Carbon Footprint Lifecycle Assessments 

The Environmental Working Group completed lifecycle assessments of the climate impact of 20 common foods, including meat, dairy, and vegetable proteins produced through conventional food production. Unlike most studies that focus on production emissions, their assessment calculates the full “farm to table” carbon footprint of each food item by examining greenhouse gas emissions generated from all phases of production. Results and methodology is discussed in detail. Data from this report was used in the Food for Thought app.

Explore Carbon Footprints by Zip Code

Investigate variations in the carbon footprint across America using an interactive map. The map, based on a recent study from Berkeley researchers Christopher Jones and Daniel M. Kammen, show that carbon reductions from living in big cities like New York, Chicago, and San Francisco, are cancelled out by higher emissions from urban sprawl surrounding those same cities. Scroll to the bottom of the page to access the maps.  

Content References

Heller, M. C., & Keoleian, G. A. (2015). Greenhouse gas emission estimates of US dietary choices and food loss. Journal of Industrial Ecology, 19(3), 391-401.


Jones, C., & Kammen, D. M. (2011) Quantifying Carbon Footprint Reduction Opportunities for U.S. Households and Communities. Supporting Materials. Environ. Sci. Technol., 45 (9), pp 4088–4095.


Jones, C., & Kammen, D. M. (2014). Spatial distribution of US household carbon footprints reveals suburbanization undermines greenhouse gas benefits of urban population density. Environmental science & technology, 48(2), 895-902.


Researchers find that carbon reductions from living in big cities like New York, Chicago, and San Francisco, are cancelled out by higher emissions from urban sprawl surrounding those same cities.


Weber, C. and Matthews, H. (2008) Food miles and the Relative Climate Impacts of Food Choices in the United States. Environ. Sci. Technol. 42(10): 3508-3513. DOI: 10.1021/es702969f


 The climate impacts of food choice in the United States are analyzed and the impacts from life-cycle transportation and life-cycle production are compared.

Website References

Carbon Calculator  –  The Nature Conservancy 


Carbon Footprint Calculator  –  U.S. Environmental Protection Agency


Climate Change and Energy Curricula  –  Climate Generation 

Draft Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2015  – U.S. Environmental Protection Agency

Footprint Calculator  –  Global Footprint Network

Greenhouse Gases Factsheet  –  Center for Sustainable Systems, University of Michigan 

How is Today’s Warming Different from the Past?  –  NASA Earth Observatory 

Interactive Carbon Calculator  –  California Cool 

Livestock – Climate Change’s Forgotten Sector: Global Public Opinion on Meat and Dairy Consumption  –  Chatham House, The Royal Institute of International Affairs 


Meat Eater's Guide  –  Environmental Working Group 

Mapping the American Carbon Footprint, Down to the Last Zip Code  –  Shrink the Footprint

Teaching the Food System from Farm to Fork  –  Foodspan, John Hopkins 

Understanding Global Warming Potentials  –  U.S.  Environmental Protection Agency

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