Pathfinding a post-fossil built environment

The latest UNEP Emissions Gap Report is unequivocal: “a quantum leap in ambition in tandem with accelerated mitigation action in this decade” is required. The gaps and urgency are particularly obvious in built environment systems: (1) only small parts of the growing global population already have access to sustainable (SDG-compliant) housing and infrastructure; (2) existing stocks are difficult to decarbonize due to their path dependence; (3) long planning cycles as well as slow decarbonization in construction and material industry.
Buildup, renewal and operation of the built environment will drive much of global energy and material demand in the next decades. As industry is decarbonizing only slowly, this induces high environmental impact. What we need are comprehensive rapid transition pathways, tailored to regional and temporal context. 
Building stock models are useful to create scenarios of future developments and test different strategies and innovations. For instance, material efficiency, circular construction, and the use of regenerative materials are highly effective strategies, as they are readily available and cost-effective. Our work has shown that these could roughly halve cumulative greenhouse gas emissions of global building stocks by 2050.
For reliable and meaningful assessments, it is important to develop adequate methods and data.  Models need to capture dynamic effects due to spatial, temporal, or physical interdependence. Data collection, harmonization and representativeness remain critical challenges.
Beyond technical solutions, the implementation gap between research, policy, and practice must be addressed. Nationally Determined Contributions (NDCs) are falling short of the Paris Agreement targets, making bottom-up initiatives, by all stakeholders, such as communities, building owners and planners, increasingly vital. The city of Zurich exemplifies how science-based approaches can drive impactful change through pioneering environmental standards and pilot projects.