Editing IPCC:AR6/WGIII/Chapter-10 (section)

=== Cross-Chapter Box 7 | Urban Form: Simultaneously Reducing Urban Transport Emissions, Avoiding Infrastructure Lock-in, and Providing Accessible Services ===

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'''Authors:''' Felix Creutzig (Germany), Karen C. Seto (the United States of America), Peter Newman (Australia)

Urban transport is responsible for about 8% of global CO 2 emissions or 3 GtCO 2 per year (Chapters 5 and 8). In contrast to energy supply technologies, urban transport directly interacts with mobility lifestyles ( [[IPCC:Wg3:Chapter:Chapter-5#5.4|Section 5.4]] ). Similarly, non-GHG emission externalities, such as congestion, air pollution, noise, and safety, directly affect urban quality of life, and result in considerable welfare losses. Low-carbon, highly accessible urban design is not only a major mitigation option, it also provides for more inclusive city services related to well-being (Sections 5.1 and 5.2). Urban planning and design of cities for people are central to realise emission reductions without relying simply on technologies, though the modes of transport favoured will influence the ability to overcome the lock-in around automobile use ( [[#Gehl--2010|Gehl 2010]] ; [[#Creutzig--2015b|Creutzig et al. 2015b]] ).

Where lock-in has occurred, other strategies may alleviate the GHG emissions burden. Urban planning still plays a key role in recreating local hubs. Available land can be used to build rail-based transit, made financially viable by profiting from land value captured around stations ( [[#Ratner--2013|Ratner and Goetz 2013]] ). Shared or pooled mobility can offer flexible on-demand mobility solutions that are efficient also in suburbs and for integrating with longer commuting trips ( [[#ITF--2017|ITF 2017]] ).

Global emissions trajectories of urban transport will be decided in rapidly urbanising Asia and Africa. Urban transport-related GHG emissions are driven by incomes and car ownership but there is considerable variation among cities with similar income and car ownership levels ( [[#Newman--2015|Newman and Kenworthy 2015]] ). While electrification is a key strategy to decarbonise urban transport, urban infrastructures can make a difference of up to a factor of 10 in energy use and induced GHG emissions ( [[#Erdogan--2020|Erdogan 2020]] ). Ongoing urbanisation patterns risk future lock-in of induced demand on GHG emissions, constraining lifestyles to energy-intensive and high CO 2 -related technologies ( [[#Erickson--2015|Erickson and Tempest 2015]] ; [[#Seto--2016|Seto et al. 2016]] ) (Sections 5.4, 8.2.3 and 10.2.1). Instead, climate solutions can be locked into urban policies and infrastructures ( [[#Ürge-Vorsatz--2018|Ürge-Vorsatz et al. 2018]] ) especially through the enhancement of the walking and transit urban fabric. Avoiding urban sprawl, associated with several externalities ( [[#Dieleman--2004|Dieleman and Wegener 2004]] ), is a necessary decarbonisation condition, and can be guided macro-economically by increasing fuel prices and marginal costs of motorised transport ( [[#Creutzig--2014|Creutzig 2014]] ). Resulting urban forms not only reduce GHG emission from transport but also from buildings, as greater compactness results in reduced thermal loss ( [[#Borck--2018|Borck and Brueckner 2018]] ). Health benefits from reduced car dependence are an increasing element driving this policy agenda ( [[#Speck--2018|Speck 2018]] ) ( [[#10.8|Section 10.8]] ).

Low-carbon highly accessible urban design is not only a major mitigation option, it also provides for more inclusive city services related to well-being (Sections 5.1 and 5.2). Solutions involve planning cities around walkable sub-centres, where multiple destinations, such as shopping, jobs, leisure activities, and others, can be accessed within a 10 minute walk or bicycle ride ( [[#Newman--2006|Newman and Kenworthy 2006]] ). Overall, the mitigation potential of urban planning is about 25% in 2050 compared with a business-as-usual scenario ( [[#Creutzig--2015a|Creutzig et al. 2015a]] ; [[#Creutzig--2015b|Creutzig et al. 2015b]] ). Much higher levels of decarbonisation can be achieved if cities take on a regenerative development approach and act as geo-engineering systems on the atmosphere ( [[#Thomson--2016|Thomson and Newman 2016]] ).

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