Previous studies showed that using carbon dioxide (CO2) as a raw material for chemical syntheses may provide an opportunity for achieving greenhouse gas (GHG) savings and a low-carbon economy. Nevertheless, it is not clear whether carbon capture and utilization benefits the environment in terms of resource efficiency. We analyzed the production of methane, methanol, and synthesis gas as basic chemicals and derived polyoxymethylene, polyethylene, and polypropylene as polymers by calculating the output-oriented indicator global warming impact (GWI) and the resource-based indicators raw material input (RMI) and total material requirement (TMR) on a cradle-to-gate basis. As carbon source, we analyzed the capturing of CO2 from air, raw biogas, cement plants, lignite-fired power, and municipal waste incineration plants. Wind power serves as an energy source for hydrogen production. Our data were derived from both industrial processes and process simulations. The results demonstrate that the analyzed CO2-based process chains reduce the amount of GHG emissions in comparison to the conventional ones. At the same time, the CO2-based process chains require an increased amount of (abiotic) resources. This trade-off between decreased GHG emissions and increased resource use is assessed. The decision about whether or not to recycle CO2 into hydrocarbons depends largely on the source and amount of energy used to produce hydrogen.
The Paris Agreement (PA) emphasizes the intrinsic relationship between climate change and sustainable development (SD) and welcomes the 2030 agenda for the global Sustainable Development Goals (SDGs). Yet, there is a lack of assessment approaches to ensure that climate and development goals are achieved in an integrated fashion and trade-offs avoided. Article 6.4 of the PA introduces a new Sustainable Mitigation Mechanism (SMM) with the dual aim to contribute to the mitigation of greenhouse gas emissions and foster SD. The Kyoto Protocol's Clean Development Mechanism (CDM) has a similar objective and in 2014, the CDM SD tool was launched by the Executive Board of the CDM to highlight the SD benefits of CDM activities. This article analyses the usefulness of the CDM SD tool for stakeholders and compares the SD tool's SD reporting requirements against other flexible mechanisms and multilateral standards to provide recommendations for improvement. A key conclusion is that the Paris Agreement's SMM has a stronger political mandate than the CDM to measure that SD impacts are "real, measurable and long-term". Recommendations for an improved CDM SD tool are a relevant starting point to develop rules, modalities, and procedures for SD assessment in Article 6.4 as well as for other cooperative mitigation approaches.