Cities

Cities

Cool roofs

Urban heat

Problem

Dark roofs and asphalt trap heat and spike energy use.

Fix

Cool roofs and reflective coatings lower temperatures and cut AC demand.

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Cities

Permeable pavement

Urban runoff and floods

Problem

Cities seal soil with asphalt. Rain becomes a dirty flood that overloads sewers and rivers instead of soaking in.

Fix

Porous asphalt, pervious concrete, and interlocking pavers let water into a stone reservoir below the street. They are standard green-stormwater kit in U.S. municipal programs, German cities, and China’s sponge-city projects. They clog without sweeping, and they are not a levee; they shave runoff on the lots and streets where they are laid.

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Cities

Urban tree canopy

Hot, bare city streets

Problem

Hard surfaces and missing shade make neighborhoods hotter than the countryside around them, especially where past planning left few trees.

Fix

Street and park trees, planted and measured as canopy cover, cool air and pavement on the blocks that have them. Cities such as New York and Melbourne run named canopy programs and track cover. Trees need water, space, and years. A “million trees” slogan without survival counts is landscaping, not climate infrastructure.

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Cities

District heating from waste heat

Buildings heated one boiler at a time

Problem

Individual gas boilers waste heat that power plants, incinerators, and industry already throw away. Cities still burn fuel in every basement.

Fix

Insulated pipe networks carry hot water from combined-heat-and-power plants, waste incinerators, data centers, and industry into buildings. Copenhagen (including heat from Amager Bakke), Stockholm, Paris, and large Chinese systems already run this way. Networks are expensive to dig, and the climate win depends on the heat source: waste heat and clean power help; a coal CHP plant is still coal.

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Cities

Green roofs

Bare roofs that shed heat and rain

Problem

Conventional roofs dump rain into sewers and bake in the sun. In a dense city that adds runoff and heat when there is no soil left at street level.

Fix

A planted roof holds growing medium and vegetation over a waterproof membrane. GSA lists more than 80 federal buildings with green roofs: about 2.2 million square feet: including the U.S. Coast Guard Headquarters in Washington, DC (557,000 square feet). GSA says a planted roof can last two or three times longer than a bare membrane, cut heat-island load, and add insulation. It still needs a sound structure, drainage, and upkeep. A sedum mat is not a park, and it does not replace street trees or sewers.

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Cities

Rain gardens and bioswales

Streets that turn rain into a dirty flood

Problem

When lots and roads are sealed, rain hits hard surfaces and races into pipes, carrying oil, sediment, and nutrients. Sewers overflow; streams spike.

Fix

EPA treats rain gardens and bioswales as types of green infrastructure. A rain garden is a shallow planted basin that collects roof and street runoff and filters it through soil, sand, or gravel. A bioswale is a linear vegetated channel that slows and treats water as it moves: useful along roads. They are not levees. Large storms still need overflow to a drain. They clog or drown plants if they are not designed and maintained.

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Cities

Cool pavements

Streets that store the day's heat

Problem

Dark asphalt soaks up sun and then heats the air and the stormwater that runs off it. EPA cites an Arizona pilot in which conventional paving reached 152°F at midday while cooler surfaces stayed 10-16°F lower.

Fix

EPA uses “cool pavement” for materials that reflect more sun, hold water so it can evaporate, or are otherwise modified to stay cooler than ordinary asphalt. Existing concrete and asphalt mixes, coatings, and grass paving all count. There is no official U.S. labeling program, and the kit is less mature than cool roofs. A lighter street is not a substitute for shade trees, and it is distinct from permeable pavement laid mainly for drainage.

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Cities

District cooling

Every tower running its own chillers

Problem

In hot, dense districts each building often keeps its own chiller plant. That wastes space, energy, and maintenance on equipment that sits idle much of the day.

Fix

District cooling makes chilled water in a central plant and pipes it to many buildings. SP Group, Singapore’s largest operator, runs Marina Bay: which it calls the world’s largest underground district cooling network: with no supply disruptions since 2006 and 28 buildings served (a planned expansion to 50 by 2030). SP also cites industrial plants and Tengah, a public-housing township with rooftop modular chillers. The climate win depends on the power and the water source. A chilled-water pipe is not a reason to keep leaking envelopes.

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Cities

Energy renovation of buildings

Buildings that leak heat all winter

Problem

The European Commission says roughly 75% of EU buildings have poor energy performance, yet the annual renovation rate is only around 1%. Households still use most of their energy for heat, cooling, and hot water.

Fix

Energy renovation is insulation, better windows, efficient heat or cooling, on-site renewables, and controls. The 2024 recast of the Energy Performance of Buildings Directive and the Renovation Wave aim to double that rate. The Commission says a deep renovation of a very poor building can cut energy use by as much as 80%. Non-residential worst performers face staged minimum standards; homes must cut average use 16% by 2030 versus 2020. Passports and one-stop shops are tools, not a guarantee. A coat of foam without ventilation or a heat source that matches the envelope is a half-job.

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Cities

Bus rapid transit

Problem

Buses stuck in the same traffic as cars

Fix

Bus rapid transit (BRT) gives buses their own lanes, level boarding and frequent service, so an ordinary route runs almost like a metro line at a fraction of the cost of rail. An international scoring guide rates each corridor as basic, bronze, silver or gold.

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Cities

Walking and cycling networks

Problem

Cities that treat walking and cycling as leftover space

Fix

Continuous, safe routes for people on foot and by bike, joined up at every junction, so short trips stop needing a car. Advice from the International Transport Forum puts the quality and safety of walking and cycling first, ahead of raw trip counts.

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Cities

Congestion charging

Problem

Free entry into jammed streets slows every trip

Fix

Drivers pay to use the busiest streets at the busiest times, which shortens queues and raises money for public transport. London, Stockholm and Singapore have run such charges for years. A World Bank review treats them as a way to manage how people travel as well as a source of revenue.

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Cities

Low-emission zones

Problem

High-polluting vehicles free to enter the densest streets

Fix

Mapped city areas where the most polluting vehicles are banned or must pay to enter, so nitrogen dioxide and fine particles fall where people live and walk. European cities already run more than 320 such zones, and cities elsewhere are adopting the same rules to encourage cleaner vehicles and more public transport, walking and cycling.

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Cities

Electric buses

Problem

Diesel fleets looping the densest routes all day

Fix

Battery buses on city routes remove tailpipe exhaust at stops and along busy streets, and cities already buy them at scale. The International Energy Agency (IEA) counted almost 70,000 electric bus sales worldwide in 2025, up 12% on the year before, and the UN Environment Programme (UNEP) helps countries and cities plan cleaner bus fleets.

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