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Carbon in Your Closet: Exploring Cotton and Biogenic Carbon Sequestration

Increasing temperatures, more extreme weather events, and frequent droughts, are all examples of the increasingly common impacts of climate change. In response, the world is organizing around several key strategies to reducing the impacts of climate change. As part of this effort the cotton industry has set goals to reduce greenhouse gas emissions (GHGs) and to increase carbon sequestered in the soil. While our initial efforts worked to quantify carbon captured in soil, Cotton Incorporated, the Australian Cotton Research and Development Corporation, and the College of Natural Resources at North Carolina State University are collaborating to quantify the benefits of carbon captured in our clothes.

Reducing the climate impacts of cotton production are important; however, current climate change calculations have yet to include the benefits of carbon temporally stored in the cotton clothing you wear.  The science on the benefits of temporally storing carbon is still evolving, but the research shows that capturing carbon in products such as your T-shirt reduces the warming of the atmosphere and creates a benefit for the environment.[1]

That’s right – by buying and owning cotton clothing instead of clothing made from petroleum, you are keeping carbon (and thus, carbon dioxide) out of the environment until the cotton decomposes, releasing the carbon as carbon dioxide (CO2). As plants like cotton grow, they capture CO2 through photosynthesis, storing it in fiber, plant stalks, and roots in the soil.[2] Sequestering CO2 from the air through photosynthesis and storing it as cotton has the effect of reducing the warming gasses in the atmosphere while using those same molecules to keep you warm on a cool day. Let’s dive into the science behind carbon capture in the stages of cotton – from fiber to textile to post-consumer use – and how to best measure this benefit of cotton.

Biogenic vs. Fossil Carbon

When measuring the impact of textiles on climate change with modeling approaches such as Life Cycle Assessment (LCA), the source of carbon is important and each carbon source is treated differently. Carbon which originates from biological sources such as animals, plants, trees and soil is called biogenic carbon.[3] This biogenic carbon is part of the natural carbon cycle, and represents how plants utilize CO2 and sequester it in biomass – like cotton. Only natural, plant and animal-based fibers have biogenic carbon whereas synthetic materials do not.

Cotton is made of biogenic carbon that removed CO2 from the atmosphere during the growth of the fiber. This sequestration has a quantifiable benefit by removing greenhouse gas emissions from the air that insulate and warm the earth. Conversely, the carbon in polyester is generally from fossil fuels that are made from carbon molecules captured millions of years ago—so long ago that they are considered fossil carbon and do not count as carbon capture.[4] The main difference is that biogenic carbon is a part of the current carbon cycle, where fossil carbon is carbon that would otherwise be out of the cycle if not for human activity. Biogenic carbon captured in cotton fiber can contribute to a net cooling effect on the planet through a reduction in radiative forcing – a benefit that increases the longer the carbon is kept sequestered.

Cotton and Carbon

Cotton fibers are made from cellulose (C6H10O5) which, by atomic weight, is more than 40% carbon. The average acre of cotton captures and temporarily stores 3,513 pounds of carbon in the lint alone. And every unit of carbon removed from the atmosphere corresponds to 3.66 pounds CO2 captured from the air.[5] The carbon captured on an acre of land is similar to the emissions from burning 657 gallons of gasoline – or 14,500 miles driven in an average gas-powered vehicle.[6]

Measuring Impact

The impact of this short-term captured carbon is not commonly quantified in LCAs, but could have a substantial impact on the overall sustainability of a fabric.[7] Cotton Incorporated and the Cotton Research and Development Corporation are working with researchers at North Carolina State University to better measure the environmental impact of biogenic carbon stored in cotton as well as research opportunities to extend the lifecycle of cotton, and thereby extend the benefits of sequestering this carbon.

This emerging area of research will help us quantify some of the natural advantages cotton already has – specifically, its durability and circularity. With biogenic carbon capture, the longer you have your cotton textiles (t-shirts, sweatshirts, jeans, towels, etc.) the longer you are helping keep CO2 out of the atmosphere. Keeping CO2 out of the atmosphere, even temporarily, helps reduce the impact of climate change.[8]

For example, 1 pair of jeans (roughly weighing 1.6 lbs) is equivalent to 2.5 lbs of CO2 sequestration.5

Cotton-rich clothing made with a higher percentage of cotton (at least 60%) is worn more often than clothing with lower cotton content, also suggesting cotton is more durable.[9]  Increased durability leads to increased garment life, keeping the captured CO2 out of the environment longer.  The longer you wear that favorite sweatshirt, the longer you will be keeping that CO2 out of the atmosphere and helping reduce the warming effect on the earth.

Building On All That Carbon Captured

Cotton Incorporated has several programs that help extend the lifecycle of cotton fabrics (and the carbon they store). Through the Blue Jeans Go GreenTM denim recycling program, recycled old denim is transformed into creative new products, from insulating material for buildings to pet bed inserts to thermal insulation used in sustainable food and pharmaceutical packaging. All of these uses help ensure the carbon stored in the cotton fabric stays sequestered and not released into the atmosphere after the first use.

Cotton is also inherently circular, meaning it is grown from the earth, can be reused and recycled in a variety of ways, and biodegrades when it is ultimately returned to the earth.

Cotton Incorporated is actively researching new ways to keep cotton, and more importantly the carbon stored in the cotton, in a physical and useful form that not only prolongs carbon storage but can also help reduce the carbon emissions of new material production.

Researchers at North Carolina State University are exploring opportunities for waste cotton to be used as bioenergy that could have significant benefits when replacing fossil fuels like coal. Another end-of-life research project involves composting cotton to make nutrients that can be applied to the fields where the cotton was grown. Researchers at Cornell University are operating industrial composting trials decomposing cotton jeans. As we look towards the future, carbon in the cotton fiber will grow in importance and increasing the life of both the first use garment use and subsequent uses will be an important strategy for reducing the apparel industries climate impacts.

At the end of the day, many of these use cases continue to sequester the carbon contained within the fabric, prolonging its benefit to the environment. At Cotton Incorporated,

our commitment is to bring the latest scientific discoveries in the world of cotton and sustainability. The sequestration of biogenic carbon in cotton is an area we feel has significant potential to add to the sustainability story of cotton. We are developing our understanding of the science and how the industry can more precisely measure and reduce our climate impacts and continue to be the responsible fiber of choice.

Jesse Daystar – Vice President, Chief Sustainability Officer

 

[1] Levasseur, A., Lesage, P., Margni, M., & Samson, R. (2013). Biogenic Carbon and Temporary Storage Addressed with Dynamic Life Cycle Assessment. Journal of Industrial Ecology, 17(1), 117–128.

[2] Payton, P., Webb, R., Kornyeyev, D., Allen, R., & Holaday, A. S. (2001). Protecting cotton photosynthesis during moderate chilling at high light intensity by increasing chloroplast antioxidant enzyme activity. Journal of Experimental Botany, 52(365), 2345-2354.

Wakelyn, P.J. (2006). Cotton Fiber Chemistry and Technology (1st ed.). CRC Press. Chapter 3 (page 15).

[3] Intergovernmental Panel on Climate Change, Glossary, (2019), https://www.ipcc.ch/site/assets/uploads/2019/06/19R_V0_02_Glossary_advance.pdf

[4] IEA Bioenergy, Fossil vs biogenic CO2 emissions, (2022). https://www.ieabioenergy.com/iea-publications/faq/woodybiomass/biogenic-co2/#

[5] Calculated based on these assumptions using a cotton carbon formula: 1. Cotton is approximately 95% cellulose 2. Cellulose is 44% carbon (based on the molecular formula for cellulose) 3. Every unit of carbon removed from the atmosphere represents 3.667 units of C02e removed (based on the molecular formula of carbon dioxide)

Source:  Wakelyn, P.J. (2006). Cotton Fiber Chemistry and Technology (1st ed.). CRC Press. Chapter 3.

[6] United States Environmental Protection Agency (2022). Greenhouse Gas Equivalencies Calculator. https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator

[7] Levasseur, A., Lesage, P., Margni, M., & Samson, R. (2013). Biogenic Carbon and Temporary Storage Addressed with Dynamic Life Cycle Assessment. Journal of Industrial Ecology, 17(1), 117–128.

[8] Levasseur, A., Lesage, P., Margni, M., & Samson, R. (2013). Biogenic Carbon and Temporary Storage Addressed with Dynamic Life Cycle Assessment. Journal of Industrial Ecology, 17(1), 117–128.

Daystar, J., Venditti, R., & Kelley, S. S. (2017). Dynamic greenhouse gas accounting for cellulosic biofuels: implications of time based methodology decisions. International Journal of Life Cycle Assessment, 22(5), 812–826.

Kendall, A. (2012). Time-adjusted global warming potentials for LCA and carbon footprints. The International Journal of Life Cycle Assessment, 17(8), 1042-1049.

[9] 2020 Cotton Council International (CCI) and Cotton Incorporated’s Global Durability Study.