Data story: Urban emissions trajectories — which cities are actually decarbonizing and how

Why It Matters

Cities occupy roughly three percent of the Earth's land surface yet produce more than 70 percent of global energy-related CO₂ emissions, according to the United Nations Environment Programme (UNEP, 2025). With urban populations projected to reach 6.7 billion by 2050 (UN-Habitat, 2025), the trajectory of city-level emissions will largely determine whether the world meets the Paris Agreement target of limiting warming to 1.5 °C. Yet aggregate numbers obscure a striking divergence: a growing cohort of cities is decoupling economic growth from carbon output while many others continue on upward emissions curves. Understanding which cities are actually reducing emissions, how fast, and through what combination of policies provides a practical blueprint for municipal leaders, investors, and sustainability professionals navigating the urban transition.

The data also reveal that per-capita metrics tell a different story than absolute totals. A megacity in South Asia may have low per-capita emissions but rapidly rising absolute volumes, while a Nordic capital may show high historical per-capita output that is now falling sharply. Tracking both dimensions is essential for fair benchmarking and effective resource allocation.

Key Concepts

Absolute vs. per-capita emissions. Absolute emissions measure the total CO₂-equivalent output of a city, while per-capita figures divide that total by population. CDP-ICLEI data for 2025 show that reporting cities have a median per-capita footprint of 4.8 tCO₂e, but the range spans from below 2 tCO₂e in cities like Bogotá to above 15 tCO₂e in Houston (CDP, 2025). Tracking both metrics prevents misleading comparisons: a city can lower per-capita emissions through population growth alone without any real decarbonization effort.

Scope 1, 2, and 3 boundaries. Most city inventories cover Scope 1 (direct combustion within boundaries) and Scope 2 (grid electricity). A smaller but growing number include Scope 3 categories such as aviation, freight, and embodied carbon in construction materials. The Global Protocol for Community-Scale Greenhouse Gas Inventories (GPC) provides a standardized framework, yet only about 40 percent of the 1,300+ cities reporting to CDP use GPC-compliant methodologies (CDP, 2025). Inconsistent boundaries make cross-city comparisons difficult and can hide significant emission sources.

Decoupling indicators. Genuine decarbonization requires absolute emissions to decline even as GDP and population grow. The C40 Cities network tracks a "peak-and-decline" metric: whether a city's emissions have peaked and are now falling on a sustained basis. As of early 2026, C40 reports that 53 of its 96 member cities have demonstrated peaking, up from 38 in 2022 (C40 Cities, 2026). However, the pace of decline in most cases remains well below the roughly 7 percent annual reduction needed for 1.5 °C alignment.

Sectoral breakdown. Urban emissions cluster in three dominant sectors: buildings (heating, cooling, and electricity), transport, and waste. IEA data indicate that buildings account for roughly 40 percent of urban energy-related emissions globally, transport for 30 percent, and industry plus waste for the remainder (IEA, 2025). The relative weight varies by geography: North American cities skew heavily toward transport, while many Asian cities have larger industrial components.

What's Working and What Isn't

Electricity grid decarbonization is the biggest single driver. Cities in regions with rapidly greening grids have seen the sharpest emission drops without needing radical local policy changes. Copenhagen reduced per-capita emissions by 80 percent between 2005 and 2025, driven largely by Denmark's national wind build-out and district heating conversions (City of Copenhagen, 2025). Similarly, cities in the UK have benefited from the national grid's coal-to-renewables shift, with London reporting a 52 percent absolute reduction since 1990 (Greater London Authority, 2025).

Transport electrification is accelerating in leading cities. Oslo now has electric vehicles comprising over 90 percent of new car sales, contributing to a 36 percent reduction in transport emissions since 2015 (City of Oslo, 2025). Shenzhen completed the full electrification of its 16,000-bus fleet in 2019 and has since expanded to electrify 70 percent of its taxi fleet, removing an estimated 1.35 million tonnes of CO₂ annually (Bloomberg NEF, 2025). However, most cities in the Global South lack the grid capacity, charging infrastructure, and subsidies to replicate these results at scale.

Building retrofits lag behind targets. Despite strong policy signals from the EU Energy Performance of Buildings Directive recast in 2024, renovation rates in European cities remain below 1.5 percent per year, well short of the 3 percent pace needed to meet 2050 targets (European Commission, 2025). Cities such as Amsterdam and Vienna have launched district-level retrofit programmes, but financing gaps and split incentives between landlords and tenants continue to slow progress.

Waste-sector emissions remain stubbornly high in emerging economies. Open dumping and uncontrolled landfills produce methane at rates 50 to 80 times more potent than CO₂ over a 20-year horizon. While cities like San Francisco have achieved 80 percent landfill diversion, rapidly urbanizing cities in Sub-Saharan Africa and South Asia still send more than 70 percent of municipal waste to open dumps (UNEP, 2025).

Data gaps undermine accountability. Only one in five cities globally publishes an annual greenhouse gas inventory using a standardized methodology. Self-reported data to platforms like CDP and the Global Covenant of Mayors often lag by two or more years and use inconsistent baselines, making it difficult to verify whether stated reductions are real (WRI, 2025).

Key Players

Established Leaders

• C40 Cities Climate Leadership Group — Network of 96 global megacities representing over 700 million people and one quarter of the global economy; sets sector-specific action pathways and publishes annual progress reports.
• ICLEI – Local Governments for Sustainability — Serves more than 2,500 local and regional governments with tools for emissions accounting, climate action planning, and biodiversity governance.
• CDP (formerly Carbon Disclosure Project) — Runs the world's largest city-level environmental disclosure platform with over 1,300 cities reporting annually.
• World Resources Institute (WRI) — Manages the GPC standard and provides technical assistance for city emissions inventories through its Urban Efficiency program.

Emerging Startups

• Kairos (Climate AI) — Uses satellite imagery and machine learning to produce near-real-time citywide emissions estimates, filling inventory gaps for municipalities without monitoring infrastructure.
• Mortar IO — Provides building-level energy and carbon analytics to cities and real estate portfolios using utility data integration and digital twins.
• ClimateView — Offers a climate transition platform used by over 100 cities to visualize emission pathways, track progress, and model policy scenarios.

Key Investors/Funders

• Bloomberg Philanthropies — Funds the American Cities Climate Challenge and supports the Global Covenant of Mayors.
• European Investment Bank (EIB) — Through its Urban Framework Loan, committed EUR 5.6 billion to urban climate projects between 2023 and 2025.
• Green Climate Fund (GCF) — Allocates roughly 30 percent of its portfolio to urban resilience and low-emission development projects in developing countries.

Examples

Copenhagen, Denmark. Copenhagen's Carbon Neutral 2025 plan fell narrowly short of its zero-emission target, but the city nonetheless achieved an 80 percent reduction in per-capita emissions relative to 2005 levels. Key levers included replacing coal-fired combined heat and power plants with biomass and waste-to-energy facilities, expanding the cycling network to 390 km, and sourcing 100 percent of municipal electricity from wind. The remaining gap is attributed to Scope 3 emissions from construction and consumption that fell outside the city's direct control (City of Copenhagen, 2025).

Medellín, Colombia. Medellín reduced transport emissions by 24 percent between 2016 and 2024 through a combination of an integrated metro, cable car, and bus rapid transit system that serves 1.2 million daily riders. The city also introduced a congestion pricing pilot in 2024 and has deployed 180 electric buses. Medellín's Green Corridors initiative planted 880,000 trees and established 30 vegetated corridors that lower urban heat island temperatures by up to 3 °C, indirectly cutting cooling-related electricity demand (C40 Cities, 2025).

Tokyo, Japan. Tokyo operates the world's first city-level cap-and-trade programme, launched in 2010 and covering approximately 1,300 large commercial and industrial facilities. By 2025, covered facilities had reduced emissions by 32 percent relative to the baseline period. The programme's success derives from mandatory annual reporting, tradeable credits, and penalties for non-compliance. Tokyo Metropolitan Government expanded the scheme in 2025 to include mid-size buildings with floor areas above 5,000 m², adding roughly 4,000 additional facilities (Tokyo Metropolitan Government, 2025).

Freetown, Sierra Leone. Representing a different development context, Freetown launched its Transform Freetown climate action plan in 2019 and has since planted 1.2 million trees under the Freetown the Treetown initiative, improving stormwater management and sequestering an estimated 28,000 tCO₂ annually. The city also piloted solar-powered waste transfer stations to reduce methane from open dumping (C40 Cities, 2025).

Action Checklist

• Adopt the GPC standard for annual city-level greenhouse gas inventories and publish results within 12 months of the reporting year.
• Set both absolute and per-capita emission reduction targets aligned with a 1.5 °C trajectory, with interim milestones every five years.
• Prioritize grid decarbonization partnerships with national utilities and regional transmission operators to accelerate renewable energy procurement.
• Establish building performance standards that mandate energy use intensity disclosure and minimum retrofit thresholds for large commercial buildings.
• Expand public transit coverage and active mobility infrastructure before introducing congestion pricing or low-emission zones.
• Invest in digital monitoring tools such as satellite-derived emissions estimates and building-level energy analytics to close data gaps and enable real-time tracking.
• Integrate Scope 3 categories, particularly embodied carbon in construction and aviation, into future inventory updates.
• Join city networks like C40 or the Global Covenant of Mayors to access peer benchmarking, technical assistance, and blended finance instruments.

FAQ

Which cities are reducing emissions the fastest? Copenhagen, Oslo, and London lead among large cities in the Global North, with absolute reductions exceeding 50 percent since 1990. Among mid-size cities, Heidelberg (Germany) and Boulder (USA) have achieved similar trajectories. In the Global South, Medellín and Bogotá stand out for transport-driven reductions, though their absolute baselines are lower. C40 reports that 53 member cities have peaked emissions, but sustained annual reductions above 5 percent remain rare outside Scandinavian capitals (C40 Cities, 2026).

Why do per-capita and absolute emissions sometimes tell different stories? A city can lower per-capita emissions simply by growing its population while total output stays flat or even rises. Conversely, a shrinking city may see per-capita figures increase even as absolute emissions fall. Analysts recommend tracking both metrics alongside GDP-intensity figures to distinguish genuine decarbonization from demographic effects. The GPC framework allows reporting of all three dimensions, but many cities still report only absolute figures.

What role does building retrofit play compared to grid greening? Grid decarbonization delivers the largest near-term gains because it reduces Scope 2 emissions across all electrified end uses simultaneously. However, building retrofits are essential for reducing heating demand, particularly in cold-climate cities still dependent on natural gas. The IEA estimates that deep retrofits can cut a building's energy consumption by 50 to 70 percent, and the cumulative effect at city scale is substantial (IEA, 2025). Without parallel action on building envelopes, cities risk locking in high gas demand even as electricity becomes cleaner.

How reliable is city-level emissions data? Reliability varies widely. Cities reporting under the GPC standard with third-party verification produce data comparable to national inventories. However, many cities rely on top-down estimates, outdated activity data, or incomplete sectoral coverage. Emerging satellite-based monitoring from organizations like Climate TRACE and startup providers is beginning to provide independent verification, but spatial resolution at the city scale is still improving (WRI, 2025).

Can cities in the Global South realistically follow the same decarbonization playbook? Not entirely. Cities in low-income countries face different constraints: rapid population growth, limited fiscal capacity, informal economies, and competing development priorities. However, leapfrog opportunities exist. Solar mini-grids can bypass fossil-intensive centralized generation, bus rapid transit can be deployed faster than metro systems, and waste-to-energy plants can address both methane emissions and energy poverty simultaneously. Targeted international finance, such as the Green Climate Fund's urban portfolio, is critical to enabling these transitions.

Sources

• UNEP. (2025). Global Status Report for Buildings and Construction 2025. United Nations Environment Programme.
• CDP. (2025). Cities A List and Disclosure Dataset 2024-2025. CDP Worldwide.
• C40 Cities. (2026). Annual Progress Report: Emissions Peaking and Decline Among Member Cities. C40 Cities Climate Leadership Group.
• IEA. (2025). World Energy Outlook 2025: Urban Energy and Emissions Chapter. International Energy Agency.
• City of Copenhagen. (2025). CPH 2025 Climate Plan: Final Progress Report. City of Copenhagen.
• Greater London Authority. (2025). London Environment Strategy: Greenhouse Gas Inventory Update. Greater London Authority.
• City of Oslo. (2025). Climate Budget 2025: Transport Sector Emissions Update. City of Oslo.
• Bloomberg NEF. (2025). Electric Vehicle Outlook: City-Level Adoption and Emissions Impact. Bloomberg New Energy Finance.
• European Commission. (2025). EU Building Renovation Wave: Progress and Gaps. European Commission.
• WRI. (2025). State of City Climate Action: Data Quality and Accountability Assessment. World Resources Institute.
• Tokyo Metropolitan Government. (2025). Cap-and-Trade Program Expansion: 2025 Progress Update. Tokyo Metropolitan Government.
• UN-Habitat. (2025). World Cities Report 2025. United Nations Human Settlements Programme.