ARTICLE IN PRESS JID: CACE [m5G;June 9, 2020;19:30] Computers and Chemical Engineering xxx (xxxx) xxx Contents lists available at ScienceDirect Computers and Chemical Engineering journal homepage: www.elsevier.com/locate/compchemeng On the carbon cycle impact of combustion of harvested plant biomass vs. fossil carbon resources Soo Hyoung Choi a,b , Vasilios I. Manousiouthakis a,∗ a Department of Chemical and Biomolecular Engineering, University of California at Los Angeles (UCLA), Los Angeles, CA, 90095, United States b Division of Chemical Engineering, Jeonbuk National University, Jeonju, 54896, S. Korea a r t i c l e i n f o Article history: Received 15 December 2019 Revised 23 May 2020 Accepted 25 May 2020 Available online 2020 Keywords: Carbon cycle Atmospheric CO 2 Biomass Fossil Renewable energy a b s t r a c t This work examines the comparative impact on the carbon cycle, of harvested plant biomass combustion vs. fossil carbon combustion. A common carbon cycle model is shown to possess limitations and incon- sistencies that lead to physically unrealistic predictions. The model is modified, so as to incorporate har- vested biomass combustion as an energy resource, and the dependence of the photosynthesis rate on leaf area, rather than vegetated land area. The newly proposed model is validated with fossil fuel usage and atmospheric CO 2 concentration data, since the beginning of the industrial revolution. Although, biomass is generally considered to be a green energy source, it is shown in this work that biomass burning may result in a higher, long term, CO 2 atmospheric concentration than fossil carbon burning, depending on the rate of burning and reforestation intensity. A close examination of the characterization of harvested biomass as a renewable energy source is warranted. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction As has been pointed out in the presentation by Manousiouthakis (2017), the PSE community needs to get more involved in the modeling and simulation of phenomena (such as the carbon cycle) related to climate change, as it has the breadth and depth of knowledge to contribute to the clarification of the underlying issues. We hope that this work will help steer the PSE community in this direction, so it can utilize its prowess in mathematical modeling and computer simulations to contribute to the quantification of the phenomena involved in climate change. Biomass is commonly believed to be a renewable energy source. Until about 2008, it was considered to be carbon neu- tral, i.e. its associated net carbon dioxide atmospheric emis- sions were considered to be zero (Wikipedia, 2019a). However, Searchinger et al. (2008) and Fargione et al. (2008) suggested that land use changes associated with biofuel production would cause so called carbon debt. Johnson (2009) indicated that biomass fuels may be more carbon positive, i.e. may lead to higher net carbon dioxide emissions, than fossil fuels because biomass harvest may reduce the amount of carbon in live plants. According to a report by Cardellichio et al. (2010), burning biomass such as wood pellets causes carbon debt, i.e. net production of more greenhouse gases ∗ Corresponding author. E-mail address: vasilios@ucla.edu (V.I. Manousiouthakis). than fossil fuels for the same amount of energy produced. They predict that if coal is replaced by biomass to generate electric- ity, the payoff by regrowth of the harvested forest takes 21 years, and if natural gas is replaced, the biomass carbon debt is not paid off even after 90 years. Gelfand et al. (2011, 2013) indicate that the carbon debt repayment periods can be significantly reduced by no-till management, and minimized by using marginal lands. Wang et al. (2015) are more optimistic, and predict that biomass can be carbon negative because of a market-driven effect, i.e. more planting as economic activity. However, Nian (2016) compared woody biomass and coal, based on life cycle analysis, and as a re- sult, asserts that wood fuel is not carbon neutral, but instead, coal may become carbon neutral, if it is connected to forest growth. Re- garding whether or not wood is a green source of energy, opin- ions are divided (Cornwall, 2017), with Whitaker et al. (2018) sug- gesting that bioenergy from perennial plants has potential envi- ronmental benefits, such as reduced greenhouse gas and improved water quality. On the other hand, Bastin et al. (2019) suggest that forest expansion is one of the most effective strategies for car- bon sequestration. Although side effects on the ecosystems and economies should also be considered (Buis, 2019), a positive re- sult has been reported by Tong et al. (2020), which indicates that southern China has recently been removing 33% of their fossil CO 2 emissions through land use changes. In this work, these issues will be investigated in the context of carbon cycle modeling. Eriksson and Welander (1956) proposed a carbon cycle model composed of four carbon pools, i.e. atmosphere, assimilating https://doi.org/10.1016/j.compchemeng.2020.106942 0098-1354/© 2020 Elsevier Ltd. All rights reserved. Please cite this article as: S.H. Choi and V.I. Manousiouthakis, On the carbon cycle impact of combustion of harvested plant biomass vs. fossil carbon resources, Computers and Chemical Engineering, https://doi.org/10.1016/j.compchemeng.2020.106942