Professional Practice
Climate Change Mitigation: Cities
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Per-capita emissions in dense urban areas tend to be lower than national averages. For example, in 2015, the average resident of New York City had an annual carbon footprint of 6.1 metric tons of carbon dioxide equivalent emissions (mtCO2e), compared to the national average of 19 mtCO2e per capita. Cities’ per capita efficiencies are largely due to the built environment: city residents use public transit more frequently and tend to live in denser, energy efficient buildings. However, cities are still responsible for 70 percent of the world’s carbon dioxide emissions due to the sheer number of urbanites, making efforts to reduce urban emissions vital.
While improving building efficiency is important to reducing urban emissions, cities can also lower their carbon footprint by increasing transit ridership, walking, cycling, and reducing car use. A 2014 study found that wider adoption of walking, cycling, and mass transit could help cities reduce transportation emissions by 40 percent, as well as save more than $100 trillion in spending and avoid an estimated 1.4 million early deaths. Multiple modes of transportation also help communities adapt to a changing climate and improve resilience -- if one transportation network fails in the event of a natural catastrophe, there are other ways to move through the city.
Landscape architects help cities design interconnected streets, parks, and plazas that encourage low-carbon ways of getting around and maximize the benefits of a dense built environment. They help cities retrofit existing infrastructure to encourage walking and biking and create safe, seamless connections to different modes of travel.
Strategies for encouraging low-emission forms of transportation include:
- Investing in reliable, accessible, affordable, frequent, and interconnected public transit service.
- Investing in safe, interconnected bicycle infrastructure, including widely accessible bike share.
- Widening sidewalks and instituting "road diets" to improve pedestrian connectivity, accessibility, and safety.
- Reducing vehicle speed limits to make streets safer for pedestrians and cyclists.
- Incorporating electric vehicle charging stations into streetscapes, plazas, parks, and parking lots.
There are other landscape-oriented strategies cities can use to further reduce emissions. Urban trees reduce a city’s overall carbon footprint by absorbing carbon dioxide, offsetting emissions. A recent study found that the urban tree canopy in some areas of London sequesters as much carbon per hectare as temperate and tropical rainforests.
Trees also reduce energy use by providing shade and lowering ambient air temperatures. A 2016 report by the Nature Conservancy found that increased investment in urban tree planting could avoid up to 13 million tons of carbon dioxide emissions annually in the form of reduced electricity demand.
Trees, parks, and other forms of urban nature also support emissions reductions goals by improving the overall quality of urban life, making life in dense cities healthier and more appealing. Studies have shown that people with access to parks and green space are more physically active, live longer, and report higher levels of overall well-being. Trees are the basis of the critical environmental systems that underpin the health and resilience of a city.
Cities can also reduce emissions through an unlikely source: compost. When food waste is sent to landfills, it decomposes and emits methane, a powerful greenhouse gas. According to Project Drawdown, food waste alone is responsible for 8 percent of annual global greenhouse gas emissions.
When that same food waste is composted, emissions are avoided and the waste is converted into valuable, carbon-rich fertilizer. Thanks to a city-wide mandatory composting and recycling ordinance enacted in 2009, San Francisco has reduced its annual GHG emissions by 93,437 metric tons per year. The compost created from the city’s food scraps is in turn sold to local farmers and wineries. Composting at an urban scale helps communities adapt to a changing food system and build community resilience as well.
Landscape architects seamlessly integrate these various elements into the urban landscape, creating public spaces and systems that support and accommodate a wide variety of emissions-reducing strategies that also help communities adapt to climate change and become more resilient.
Organizations
C40 Cities
The Trust for Public Land
Urban Land Institute
The Nature Conservancy
Resources
Cities' Contribution to Climate Change, World Bank
D.C. Becoming More Sustainable, But Not Everyone Benefits, The Dirt blog, 2017
Recycling's 'Final Frontier': The Composting of Food Waste, YaleEnvironment 360, August 8, 2013
Zero Waste Case Study: San Francisco, U.S. Environmental Protection Agency
Urban Trees Can Store Almost as Much Carbon as Tropical Rainforests, Fast Company, June 27, 2018
Urban Nature for Human Health and Well-Being: A Research Summary for Communicating the Health Benefits of Urban Trees and Green Space, U.S. Department of Agriculture, February 2018
Research
Estimating Urban above Ground Biomass with Multi-Scale LiDAR, Phil Wilkes, Mathias Disney, Matheus Boni Vicari, Kim Calders, and Andrew Bert, Carbon Balance and Management, June 2018
A Global High Shift Scenario: Impacts and Potential for More Public Transport, Walking, and Cycling with Lower Car Use, Michael A. Replogle, Institute for Transportation and Development Policy, and Lewis M. Fulton, University of California, Davis, 2014
Global Scenarios of Urban Density and its Impacts on Building Energy Use Through 2050, Burak Güneralp et al, Proceedings of the National Academy of Sciences of the United States of America, 2017
Human-Nature for Climate Action: Nature-Based Solutions for Urban Sustainability, Helen Santiago Fink, Sustainability, 2016
The Influence of Urban Form on GHG Emissions in the U.S. Household Sector, Sungwon Lee & Bumsoo Lee, Energy Policy, May 2014
Projects
50,000 Trees, University of California, Berkeley
Sarah Moos, Student ASLA
Adding Green to Urban Design, Chicago, IL
City of Chicago
GreenPlan Philadelphia, Philadelphia, PA
Wallace Roberts & Todd
Portland Mall Revitalization, Portland, OR
ZGF Architects LLP
Transit Revitalization Investment District (TRID) Master Plan, Philadelphia, PA
Interface Studio LLC
City Climate Plans
1.5°C: Aligning New York City with the Paris Climate Agreement
Seattle Climate Action Plan
pLAn: Transforming Los Angeles
Portland and Multnomah County Climate Action Plan
Sustainable DC