Cities Are Acting on Climate, But the Boldest Health Wins Remain Untested

Cities around the world are on the front line of the climate crisis, and a sweeping new analysis of the evidence has found that while many urban climate actions deliver real health benefits, the transformative, city-wide interventions needed to meet climate targets and unlock large-scale health gains have yet to be implemented and rigorously evaluated anywhere. The study, published in Nature Cities by a large international team led from the London School of Hygiene and Tropical Medicine, is one of the most comprehensive attempts to date to answer a deceptively simple question: when cities actually act on climate change, what happens to the health of their residents?

The research took the form of an umbrella review, a method that sits at the top of the evidence hierarchy. Rather than examining individual studies, the team systematically collected and appraised systematic reviews of implemented city-level actions whose primary or secondary purpose was both to mitigate climate-active pollutants, meaning greenhouse gases and black carbon, or to adapt to climate impacts, and to produce a health co-benefit. The search covered literature published between 2009 and 2024 across thirteen databases, spanning health, environmental science and the built environment. From 5,550 records identified, 198 reports underwent full-text assessment, 60 reviews were critically appraised, and 49 reviews with sufficient confidence in their findings were included in the final synthesis.

The sectors covered were telling. Most of the evidence clustered around transport, with 25 reviews, and urban form, with 27 reviews, followed by buildings with 13. Only three reviews each addressed food and waste. The authors note that this distribution mirrors where local governments have the greatest policy leverage, since transport, built environment and urban planning decisions are typically made at the municipal level, whereas national governments dominate energy and food systems. Crucially, the review focused on implemented actions, actual policies, programs and projects, rather than modeled projections of what might happen if cities were to act.

The clearest health co-benefits emerged from two domains: active transport and housing. In the transport sector, interventions such as traffic restrictions, congestion charging zones and improved public transport infrastructure improved health through two main pathways, better air quality and increased physical activity. The relative importance of these pathways varied geographically, with air quality improvements reported more often in low- and middle-income countries and physical activity gains in high-income countries. The magnitude of air quality benefits depended heavily on intervention scale and baseline emissions. Some findings were strikingly specific: switching to electric vehicles cut carbon dioxide per vehicle kilometer traveled by up to 20 percent even when the electricity was coal powered, while low-emission zones were associated with reductions in particulate matter of up to 17 percent. Conversely, switching from petrol to natural gas actually increased coarse particulate pollution by 15 percent in one study, a reminder that not all fuel substitutions are created equal.

In the buildings sector, home energy efficiency improvements, particularly insulation for warmth, were associated with appreciable health gains, mainly through improved thermal comfort, which is linked to better cardiovascular health. Coal bans in some settings produced reductions in particulate matter and black smoke of up to 70 percent, with mortality rate decreases of 5 to 10 percent attributed to such measures. But the evidence also flagged trade-offs: two reviews reported that inadequate ventilation in energy-efficient homes could worsen indoor air quality, underscoring that climate interventions must be designed holistically. Sustainable design and construction showed median carbon footprint reductions of 52 percent compared with conventional approaches, although this evidence did not extend to the city scale. Green roofs and walls consistently delivered environmental benefits, including reduced urban heat exposure and lower energy use.

Urban form interventions, the design and planning decisions that shape how liveable and environmentally performant cities are, produced some of the most consistent findings. Measures to increase walkability, including walking and cycling paths, street redesign, access to recreational facilities and higher residential density, were associated with increased physical activity in 14 reviews, and some evidence pointed to reductions in road traffic injuries. Access to green space was linked to improved social connectedness, reductions in perceived crime, better mental health and well-being, and improved thermal comfort through the cooling effect of vegetation. In low-income settings, community gardens were associated with reduced outbreaks of infectious disease and air pollution, and contributed to improved food security. Notably, greenhouse gas emissions were generally not assessed in these studies, with some inferring carbon reductions from reduced vehicle kilometers traveled, a gap the authors identify as symptomatic of incomplete evaluation.

The waste and food sectors revealed both promise and peril. Anaerobic digestion and aerobic composting of organic waste were documented to reduce carbon dioxide equivalent emissions per ton of waste, while biodigesters with biogas collection offered effective mitigation. On the darker side, exposure to solid waste incineration was associated with substantial harms, including increased mortality and cardiovascular disease among women, pre-term births and congenital anomalies. In the food sector, no reviews of implemented sustainable diet actions at the urban level were found at all, even though national-level evidence exists. Urban agriculture could reduce emissions and enhance biodiversity, but was considered unlikely to improve health unless accompanied by dietary shifts toward locally produced fruits and vegetables.

Perhaps the most sobering findings concerned the quality of the evidence itself. Using the AMSTAR 2 critical appraisal tool, adapted for the field, the team rated the majority of the 60 reviews as low confidence, with 11 rated critically low and excluded from the synthesis. Only six reviews, all from the buildings, transport and urban form sectors, achieved medium or high confidence. The methodological weaknesses were pervasive: fewer than half of the reviews reported independent screening by two or more reviewers, only about a third reported duplicate data collection, and fewer than 2 percent formally tested for publication bias. Most reviews were restricted to peer-reviewed English-language literature, potentially missing transformative actions reported in gray literature or non-English sources. Very few calculated effect sizes using consistent metrics or performed meta-analyses. Worryingly, there was no evidence that review quality had improved over the fifteen-year period studied.

The review also examined equity, with troubling results. Of the 22 reviews that considered impacts on equity, 16 found inadequate information in the underlying studies to make any assessment at all. Where evidence existed, it cut both ways: housing interventions targeted at low socioeconomic or vulnerable groups reduced inequity, while built environment changes to promote physical activity sometimes benefited wealthier groups more than others. This blind spot matters because climate actions that widen disparities risk undermining the political coalitions needed to sustain them.

The authors distilled four critical policy implementation gaps. First, a lack of transformative systems thinking, driven by the sectoral division of city governments that fragments public health, transport, planning and economic perspectives. Second, a failure to account for externalities and trade-offs in policy assessment, exemplified by transport appraisals that prioritize travel time while ignoring health and carbon benefits. Third, a lack of robustly designed impact evaluations, with most studies examining technological solutions rather than the policies that enable them, and randomized or natural experimental designs remaining rare. Fourth, a failure to engage community-driven initiatives, which is particularly consequential in low- and middle-income countries where urban growth concentrates in informal settlements often neglected by formal policy.

In response, the team proposes a new governance paradigm: institutionalized transdisciplinary teams working across sectors and scales, embedding health and environment into core city planning; systematic assessment of co-impacts before implementation, supported by expanded economic evaluation that captures the full societal return, including standardized metrics such as years of life gained per 100,000 people and kilotons of carbon dioxide equivalent per 100,000 people; robust evaluation built into policy from inception, with research funders financing evaluation alongside implementation; and governance structures that identify and scale up community-driven innovations rooted in existing social networks.

The conclusion is blunt and, in its way, hopeful. The greatest barrier to urban transformation is not a lack of knowledge about technical solutions, but a failure of prevailing governance paradigms to deliver cross-sectoral action at scale. Except for some housing interventions, most implemented urban actions were those that are easy and quick to set up, such as travel plans and new bike lanes, while no empirical documentation of transformative city-wide action was found anywhere. As cities grapple with rising temperatures, air pollution and growing populations, this analysis makes clear that the blueprint for healthier, low-carbon cities exists in fragments, but assembling it will require political will, better evaluation and a fundamental rethink of how city governments work together.

Subject of Research: Health co-benefits of implemented climate change mitigation and adaptation actions in cities

Article Title: Systematic overview of climate actions for health in cities

Article References: Hutchinson, E., Schuster, T. M., Crane, M., Milner, J., Belesova, K., Picetti, R., Lloyd, S., Turcu, C., Falconer, J., Anton, B., Newbould, R., Benton, L., Reynolds, T., Murage, P., Bahl, V., Milojevic, A., Sammut, S., Davies, M., Wilkinson, P., … Haines, A. (2026). Systematic overview of climate actions for health in cities. Nature Cities. https://doi.org/10.1038/s44284-026-00515-y

Image Credits: AI Generated

DOI: 10.1038/s44284-026-00515-y

Keywords: climate change, urban health, cities, systematic review, active transport, air pollution, housing, urban form, green space, health co-benefits, governance, Nature Cities