Reducing food waste is widely recognized as critical for improving resource efficiency and meeting the nutritional demand of a growing human population. Here we explore whether the sharing economy can provide meaningful assistance to reducing food waste in a relatively low-impact and environmentally-sound way. Analyzing 170,000 postings on a popular peerto-peer food-sharing app, we find that over 19 months, 90t of food waste with an equivalent retail value of £0.7 million were collected by secondary consumers and diverted from disposal. An environmental analysis focused on Greater London reveals that these exchanges were responsible for avoiding emission of 87-156t of CO 2 eq. Our results indicate that most exchanges were among users associated with lower income yet higher levels of education. These findings, together with the high collection rates (60% on average) suggest that the sharing economy may offer powerful means for improving resource efficiency and reducing food waste.

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Africa is currently experiencing rapid population growth and accelerated urbanization. This demographic shift will require a large amount of new construction material resulting in substantial environmental impact. For many cities on the continent, data gaps make specific quantification and robust prediction of this impact highly difficult. This article presents a method to assess the stock dynamics and embodied emissions of a rapidly growing urban built environment using a bottom-up, typological approach. This approach allows for the identification of appropriate engineering solutions for decarbonization by localizing embodied greenhouse gas (GHG) emissions in the different constructive elements with a revisited Sankey diagram. Different alternatives regarding housing type and construction techniques are compared. The city of Johannesburg is used as a case study to illustrate the relation between building types, technologies, and embodied GHG of its residential building stock. This new visualization uncovers the most material-and GHG-intense dwelling types and building elements. The adapted Sankey represents the building stock and its drivers in a simple way, allowing clear understanding of the consequences of potential alternatives. The business-as-usual scenario indicates 100.5 megatons carbon dioxide equivalent (Mt CO 2eq) for new construction between 2011 and 2040. The results of the dynamic model over time show that only a combination of a densified building stock with multistory buildings and the use of alternative construction materials and techniques show real potential to decelerate GHG emissions (33.0 Mt CO 2 -eq until 2040) while aiming to provide adequate and sustainable housing for all.

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