Editing IPCC:AR6/WGIII/Chapter-8 (section)

=== 8.4.1 Avoiding Carbon Lock-in ===

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Carbon lock-in occurs as the result of interactions between different geographic and administrative scales (institutional lock-in) and across sectors (infrastructural and technological lock-in), which create the conditions for behavioural lock-in covering both individual and social structural behaviours ( [[#Seto--2016|Seto et al. 2016]] ) (see Glossary for a broader definition of ‘lock-in’). The way that urban areas are designed, laid out, and built (i.e., urban form) affects and is affected by the interactions across the different forms of carbon lock-in (Figures 8.15 and 8.16). Cities are especially prone to carbon lock-in because of the multiple interactions of technological, institutional, and behavioural systems, which create inertia and path dependency that are difficult to break. For example, the lock-in of gasoline cars is reinforced by highway and energy infrastructures that are further locked-in by social and cultural preferences for individual mobility options. The dominance of cars and their supporting infrastructures in auto-centric urban forms is further reinforced by zoning and urban development patterns, such as dispersed and low-density housing distantly located from jobs, that create obstacles to creating alternative mobility options ( [[#Seto--2016|Seto et al. 2016]] ; [[#Linton--2021|Linton et al. 2021]] ).

Urban infrastructures and the built environment are long-lived assets, embodying triple carbon lock-ins in terms of their construction, operations, and demolition ( [[#Creutzig--2016b|Creutzig et al. 2016b]] ; [[#Seto--2016|Seto et al. 2016]] ; [[#Ürge-Vorsatz--2018|Ürge-Vorsatz et al. 2018]] ). There is much focus in the climate change literature on the operational lifetimes of the energy sector, especially power plants and the electricity grid, which are between 30 and 60 years ( [[#Rode--2017|Rode et al. 2017]] ). Yet, in reality, the lifespans of urban infrastructures, especially the basic layout of roadways, are often much longer (Reyna and Chester 2015). A number of detailed case studies on the evolution of urban road networks for cities around the world reveal that the current layout of streets grew out of street networks that were established hundreds of years ago ( [[#Strano--2012|Strano et al. 2012]] ; [[#Masucci--2013|Masucci et al. 2013]] ; [[#Mohajeri--2014|Mohajeri and Gudmundsson 2014]] ). Furthermore, there is evidence that urban street layout, population growth, urban development, and automobile ownership co-evolve ( [[#Li--2019a|Li et al. 2019a]] ).

For cities to break out of mutually reinforcing carbon lock-in, it will require systematic transformation and systems-based planning that integrates mitigation strategies across sectors and geopolitical scales. Urban energy demand patterns are locked-in whenever incremental urban design and planning decisions, coupled with investments in long-lasting infrastructure, such as roads and buildings, take place ( [[#Seto--2016|Seto et al. 2016]] ). The fundamental building blocks of cities are based on the layout of the street network, the size of city blocks, and the density of street intersections. If not significantly altered, these three factors will continue to shape and lock-in energy demand for decades after their initial construction, influencing the mitigation potential of urban areas ( [[#8.4.2|Section 8.4.2]] and Figure 8.22).

Avoiding carbon lock-in inherently involves decisions that extend beyond the administrative boundaries of cities. This includes pricing of low-emissions technology or materials, such as electric battery or hydrogen vehicles and buses, although cities can support their development and deployment (Cross-Chapter Box 12 in [[IPCC:Wg3:Chapter:Chapter-16|Chapter 16]] on Transition Dynamics). In contrast, urban governments in most parts of the world do have powers to set building codes that regulate materials and construction standards for buildings, including heating and cooling technologies, and major appliances. Other examples include zoning that determines the location of buildings, land uses, standards for densities, and the inclusion of energy planning in their building standards and public works, including streets, parks, and open spaces ( [[#Blanco--2011|Blanco et al. 2011]] ; [[#Raven--2018|Raven et al. 2018]] ).

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