Challenges of Urban Sustainability

By the end of this lesson, students will be able to (per CED LO SPS-6.B):

• Describe the effectiveness of different attempts to address urban sustainability challenges (per LO SPS-6.B).
• Identify and explain the six challenges named in EK SPS-6.B.1: suburban sprawl, sanitation, climate change, air and water quality, the large ecological footprint of cities, and energy use.
• Identify and explain the four responses named in EK SPS-6.B.2: regional planning, brownfield remediation and redevelopment, urban growth boundaries, and farmland protection policies.
• Apply Skill 2.D: explain the significance of geographic similarities and differences among different locations and at different times as it relates to response effectiveness.
• Evaluate which responses have strong evidence of success, which are mixed, and what trade-offs each creates.

Unit 6.11 is the framing lesson for sustainability. Lesson 6.8 introduced sustainable design practices (New Urbanism, transit-oriented development, greenbelts). Lesson 6.11 steps back to the system level: what challenges do cities face overall, and which policy responses actually work? The CED packages this into two tight essential-knowledge statements. Both are heavily tested.

Skill 2.D: comparing across places and times

The suggested skill is 2.D: explain the significance of geographic similarities and differences among different locations and/or at different times. This framing is essential: the same challenge plays out differently in Atlanta than in Tokyo; the same response produces different results in 1970s Portland than in 2020s Nashville. Effectiveness is always place-specific and time-specific. The AP exam rewards students who can articulate that significance, not just describe isolated cases.

Sprawl is low-density, auto-oriented, spatially discontinuous expansion of the urban fringe. It consumes land faster than population grows.

Sanitation challenges fall into two families: aging infrastructure in Global North cities, and informal infrastructure in rapidly-growing Global South cities. Older US cities (Chicago, Washington DC, Philadelphia, Boston) use combined sewer systems that carry stormwater and sewage in the same pipe; during heavy rain they overflow raw sewage into waterways. In Mumbai's Dharavi and Nairobi's Kibera, open sewers run alongside footpaths and flood into homes during monsoon rains. Cape Town's 2018 "Day Zero" drought nearly made a major city the first modern metro to run out of water — a climate-driven sanitation crisis that saw reservoirs drop below 15 percent capacity before emergency rationing averted the cutoff.

Climate change threatens cities through multiple pathways.

• Urban heat island: dark paving and roofing, waste heat, and lack of vegetation make cities run 2–8°F hotter than surrounding rural areas. The differential widens during heat waves, driving cooling-related deaths that concentrate in older, poorer neighborhoods.
• Coastal flooding: Miami's sunny-day flooding during king tides; Jakarta's northern districts, which are sinking one meter per decade; Dhaka's vulnerability to cyclone storm surge; Venice's MOSE flood barriers.
• Permafrost failure: Fairbanks, Alaska and other circumpolar cities watch foundations shift as ice-rich soil thaws, forcing costly structural retrofits.
• Sinking capitals: Jakarta's subsidence combined with sea-level rise prompted Indonesia's 2019 decision to relocate its capital to Nusantara in Kalimantan. That decision ties climate change directly to top-level urban policy.

Urban air and water quality crises recur across the 20th and 21st centuries and drive some of the most important environmental policy.

• Mexico City: the 1990s PM2.5 crisis ranked among the worst on Earth. Two decades of aggressive policy (emissions testing, cleaner fuels, Metro expansion) have cut concentrations sharply, yet the city still exceeds the WHO limit by 2–3 times.
• Beijing airpocalypse: winter heating fires coal, trapping PM2.5 over the North China Plain. Beijing's Air Quality Index regularly reaches "hazardous" (300+) during inversions.
• Los Angeles smog: the 1950s–60s smog crisis birthed the California Air Resources Board (CARB, 1967), which became the nation's strictest emissions regulator and a preview of federal action. The Donora (Pennsylvania) smog disaster of 1948 killed 20 and focused US attention on industrial air pollution.
• Flint, Michigan: the 2014–present water crisis began when a cost-cutting water-source switch corroded lead service lines. It exposed how aging water infrastructure in declining US cities threatens public health. Lead remediation in Flint remains incomplete.
• London Great Smog of 1952: a temperature inversion trapped coal smoke over the city, killing an estimated 12,000 residents in four days. The disaster prompted the UK Clean Air Act of 1956 — the first modern comprehensive air-quality law.

The CED specifically flags "the large ecological footprint of cities." The numbers are striking: cities house roughly 55 percent of humans (on the way to 68 percent by 2050), on about 3 percent of land surface — yet they consume roughly 78 percent of global energy and generate about 60 percent of greenhouse gas emissions. The arithmetic is that urban consumption of food, water, materials, and energy reaches far beyond city boundaries. Geographers call this an ecological shadow: the land outside the city that supports it. Per-capita footprints diverge sharply: US, Canadian, and Australian urbanites consume 4–6 global hectares per person; Indian urbanites consume under one. Singapore has a tiny national land area but a vast ecological shadow in palm-oil plantations, ocean fisheries, and imported gravel.

Urban energy use decomposes into three buckets.

• Building energy: heating, cooling, lighting. LEED and Passivhaus certification programs target net-zero or near-net-zero building performance. District energy systems (centralized heating/cooling plants serving many buildings) can cut consumption dramatically.
• Transport energy: the single-occupant automobile is the least efficient widely-used transport mode. Transit-oriented development (see 6.8) and dense cities cut transport energy per capita by more than half.
• Embodied energy: concrete and steel production each generate substantial carbon. Renovating existing buildings usually beats new construction on carbon grounds.

Reykjavik illustrates the upper bound of what is possible: nearly all of Iceland's capital is heated by geothermal district energy, and almost all its electricity is renewable. Not every city has volcanoes underneath, but the example shows what total decarbonization of urban energy looks like.

Skill 2.D asks students to explain the significance of geographic similarities and differences. Three paired comparisons illustrate how the same challenge produces different outcomes depending on place and time.

LO SPS-6.B asks students to describe the effectiveness of these responses. Honest assessment resists cheerleading. Each response has an evidence base for what it does well and what trade-offs it creates.

• Regional planning: works well where enabling legislation is strong (Portland Metro, the UK Greater London Authority). Weakens where jurisdictions can simply opt out.
• Brownfield remediation: strong environmental wins. Recurring risk: gentrification. The High Line's adjacent neighborhoods saw property values rise sharply, displacing longtime residents.
• Urban growth boundaries: Portland's UGB cut sprawl measurably but raised housing costs inside the line. The trade-off is real. Some evidence that periodic boundary expansions can release the pressure.
• Farmland protection: preserves agricultural land. If paired with a UGB, contains growth. If unpaired, pushes growth to leapfrog exurbs beyond protected parcels, sometimes worsening the sprawl footprint.

The takeaway for students: no single response solves urban sustainability. The responses work best in combination, tailored to local political, legal, and physical geography. That is the Skill 2.D point.

Four cases, each illustrating a different challenge or response from EK SPS-6.B.1 and B.2.

United States · Portland UGB Exemplar

Portland Metro UGB, 1973–present

Portland's UGB is the most-studied American sprawl-containment policy. State law (Oregon Senate Bill 100, 1973) required every city to draw a UGB; Portland's is managed by Metro, the only elected regional government in the US. Density rose, per-capita VMT fell, and farmland surrounding the metro remained productive. Housing costs rose faster than the national average.

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Germany · Emscher Park Brownfield

Ruhr Valley, 1989–1999 IBA decade

The International Building Exhibition Emscher Park (IBA 1989–1999) transformed 800 square kilometers of the Ruhr coal-and-steel heartland. Former blast furnaces became climbing walls (Duisburg-Nord); the Emscher River was re-engineered from an open sewer back toward ecological function; a regional green corridor linked what had been disconnected industrial sites. A model for post-industrial remediation.

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Indonesia · Jakarta Climate + Sanitation Crisis

Sinking 1 m/decade; capital moving to Nusantara

Northern Jakarta is sinking faster than almost any other coastal megacity, driven by groundwater extraction and compounded by sea-level rise. Flooding, saltwater intrusion into drinking water, and inundation of low-lying neighborhoods prompted the 2019 national decision to relocate the capital to Nusantara in Kalimantan. The case combines climate change, sanitation (water-supply failure), and the limits of incremental response.

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Brazil · Curitiba Regional Planning + BRT

BRT since 1974; >80% transit mode share peak

Under mayor Jaime Lerner in the 1970s, Curitiba chose to build integrated Bus Rapid Transit rather than expand highways, and coupled transit with structural land-use planning around transit corridors. BRT ridership peaked above rail-equivalent levels and the concept spread worldwide (Bogotá TransMilenio, Guangzhou BRT, many US cities). An early model of regional-planning effectiveness.

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1. Per EK SPS-6.B.1, the CED names six challenges. For your nearest metropolitan area, which two challenges are most pressing? Justify using evidence and explain why these two outrank the others locally (Skill 2.D).
2. Compare Portland's UGB with Atlanta's sprawl pattern. What geographic similarities do the two metros share, and what differences explain the divergent outcomes? (Skill 2.D — comparing two cities.)
3. Compare London's response to the 1952 Great Smog (UK Clean Air Act 1956) with Delhi's response to recurring 2010s–2020s air-quality crises. What does the time difference tell us about institutional capacity and policy windows? (Skill 2.D — comparing two time periods.)
4. Brownfield redevelopment delivers environmental wins but recurrent gentrification risk. Using one named example (the High Line, Emscher Park, or Millennium Park), describe the trade-off and propose one policy tool to mitigate displacement.
5. If a state that currently has no UGB statute were considering adopting one, which three design choices from Oregon's experience would you emphasize, and which would you modify? Defend using effectiveness evidence from lesson 6.11.

Lesson 6.11 closes Unit 6. Looking back across the eleven lessons, the unit traces an arc from urban systems (6.1 origins, 6.2 cities across the world, 6.3 globalization, 6.4 size and distribution) through urban form (6.5 internal structure, 6.6 density and land use, 6.7 infrastructure), into responses and analysis (6.8 sustainable design, 6.9 urban data, 6.10 socioeconomic challenges, 6.11 environmental challenges and system-level responses). The through-line is that cities are simultaneously humanity's greatest engine of productivity, innovation, and cultural exchange, and its greatest concentration of environmental and social challenges. The four CED-named responses (regional planning, brownfield remediation, UGBs, farmland protection) are not a complete toolkit, but they anchor the unit's answer to the question "what do we actually do about it?"

Draft alignment — pending educator review. AP HG codes correspond to the official College Board Course and Exam Description (Effective Fall 2020, V.1). Statements below are paraphrased in CountryReports' own voice; refer to the College Board's published CED for verbatim wording.

AP® and Advanced Placement® are registered trademarks of the College Board. The College Board was not involved in the production of this material and does not endorse it. Standards statements above are paraphrased; codes refer back to the official College Board CED, the NCSS C3 Framework, the Common Core State Standards, and other cited frameworks.