The Factors of Urban Morphology in Greenhouse Gas Emissions: A Research Overview
Michael Mehaffy, Stuart Cowan, Diana Urge-Vorsatz
Presented at the International Alliance of Research Universities Scientific Congress on Climate Change, March 10, 2009.
(Download the full paper here.)
Summary of Key Conclusions
1) The morphology (characteristic shape) of urban systems is a key determinant of their structural efficiency and their efficiency of energy use. This morphology can be and is actively shaped by policy, interacting with market forces and other factors.
2) Sprawling, low-density urban development has a dramatically higher level of energy use per capita than higher-density, mixed use, multi-modal development, and in some metrics may be higher by a factor of three or more.
3) Transportation energy is one important factor; but there are many other factors that must be considered, including embodied energy in infrastructure, operating energy for infrastructure, transmission and other losses, loss of ecosystem services, heat island and albedo effects, characteristic size and morphology of dwelling, embodied energy in typical dwellings, characteristic consumption patterns and induced demand, and other factors.
4) Taken together, the delta of energy use may be as high as or higher than one-third of all energy consumed, with a similar magnitude for emissions.
5) The developing world is rapidly building inefficient infrastructure and urban morphology, with very serious implications for the growth of emissions. Even the developed world is losing valuable opportunities to increase the efficiency of urban morphology.
6) Tools are readily available to shape growth, including urban codes, regulations, plans and frameworks, pricing signals, certification systems, incentives, catalyst projects, and other proven tools. These tools can be combined into locally appropriate “toolkits” for effective management of growth and emissions.
7) The effect of urban morphology is slow, but persistent, cumulative and powerful. Far from being an inconsequential driver of emissions, because of its persistent nature, it is one of the largest, and therefore its management is one of the most urgent – if sometimes overlooked - policy challenges.
The effect of automobile-dominated urban morphology on energy use and emissions is profound, and well-documented. Residents in the Bay Area of California produce up to three times more CO2 emissions per household for transportation, depending on their regional urban morphology. (Bay Area Metropolitation Transportaiton Commission, 2007.)
But so-called “tailpipe emissions” are just the beginning of the story. Another 50% of energy use and emissions can be traced to fuel production, vehicle manufacturing and maintenance, construction and maintenance of the road network, and coolant leakage. (Summarised in Hydro-Québec, 2005.)
Even this only accounts for perhaps half of the total energy and emissions from urban morphology. We must also include embodied energy in infrastructure; operating energy for infrastructure; transmission and other losses; loss of ecosystem services; heat island and albedo effects; characteristic size and morphology of dwelling; embodied energy in typical dwellings; characteristic consumption patterns and induced demand; and other factors. We believe these may well equal or exceed the previous factors.
Tools are available to manage urban morphology effectively. But it is urgent to develop them to fit local conditions and requirements.
Urban codes. Define urban form; promote density, mixed use and transit.
Other regulations and prohibitions. Regulate sprawling patterns.
Plans and frameworks. Target low-energy and low-emissions opportunities.
Certification systems. Provide a standard as a promotional tool.
Catalyst projects. Deliberately created to trigger associated positive growth by others.
Pricing signals. Include taxes, tolls, fees, surcharges, credits, deductions, offsets etc.
Other incentives. May include award schemes, grants, education campaigns, policy reports and conclusions, research dissemination, and other non-pricing influences.
Self-organisation management strategies. Promote bottom-up growth by many actors through the use of shared resources.
“Toolkits.” Combinations of tools customized for specific local systems and conditions.
CONCLUSION: The combined possible reductions in total energy use outlined above may be on the order of one-third of total global energy usage at present, and possibly more in the future. Therefore we believe this subject is an urgent policy priority.
Left: CO2 emissions per household in the San Francisco Bay Area in 2007, with 17.5 lbs per day or less in green, and 53 lbs. per day in red. (Bay Area Metropolitan Transportation Commission, 2007.) Above: The hidden energy of auto use. Summarised in Hydro-Québec (2005). Greenhouse Gas Emissions from Transportation Options. Accessed from www.hydroquebec.com/developpementdurable, 27 February 2009.
Even this is less than half of the total energy picture from urban morphology.