Comparing climate impacts of biological and technical pathways of carbon capture and utilisation

Abstract

Global carbon dioxide (CO2) levels and surface temperature have risen despite our efforts to reduce greenhouse gas (GHG) emissions. To still achieve our climate goal to limit global temperature rise under 1.5 °C, different carbon capture and utilisation (CCU) pathways have been proposed as one of the solutions to reduce GHG emissions. However, before these CCU technologies are applied, climate impacts of the technologies should be studied first, including their whole life cycles, so that the reductions of GHG emission can be guaranteed. Thus, the goal of this dissertation is to assess climate impacts of selected biological and technical CCU pathways from cradle to gate, while also highlighting the major uncertainties in each pathway. The chosen products are straw, willow biochar and low-density polyethylene produced with power-to-x chain (e-LDPE). Straw and willow biochar represent the biological pathway, while e-LDPE represents the technical pathway for CCU. Climate impacts of these products were assessed using the life cycle assessment method. According to the results, the climate impact of straw production was 0.33 kgCO2eq/kg of straw, willow biochar production was −1.9 kgCO2eq/kg of biochar and e-LDPE production was 0.26 kgCO2eq/kg of e-LDPE. However, if the carbon embedded in the products is considered, more carbon is embedded in all the products than is released during their production. Thus, they might enable a short-term carbon storage or delayed emissions. In the case of biochar where biochar is incorporated in the soil, longer-term carbon storage can be achieved. In the studied technical pathways, carbon flows are more easily measured and observed which reduces the uncertainties of climate impacts. Whereas, when compared to biological pathways, complex soil mechanics increase the uncertainties for assessing the climate impacts of those pathways. These mechanics should be further studied to reduce the uncertainties in assessing climate impacts together with assessing the impacts of the whole life cycle.