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Excessive heat is a major and growing risk for urban residents. Urban trees can significantly reduce summer peak temperatures, thus reducing heat-related mortality, morbidity, as well as cooling energy demand. However, urban tree canopy is inequitably distributed in US cities, which has been shown to contribute to higher summer temperatures in people-of-color (POC) neighborhoods. Here, we utilize a unique dataset of high-resolution tree canopy cover to estimate the inequality in summertime heat-related mortality, morbidity, and electricity consumption across a sample of 5,723 US municipalities and other places, housing 180 million people during the 2020 census (50.6% in majority non-Hispanic white neighborhoods, 49.4% in majority people-of-color, POC, neighborhoods). We also model the potential to increase tree cover in these municipalities in 5% increments up to a realistic maximum, the 90th percentile of tree cover observed in each municipality for each impervious surface class. On average, trees in non-Hispanic white neighborhoods cool the air by 0.19 ± 0.05⁰C more than in POC neighborhoods, leading annually to trees in white neighborhoods helping prevent 190 ± 139 more deaths, 30,131 ± 10,406 more doctors’ visits, and 1.4 ± 0.5 terawatt-hours (TWhr) more electricity consumption than in POC neighborhoods. The greatest inequality in the protective value of trees occurs in the Northeastern US. We estimate that for these 5,723 municipalities, the maximal feasible urban reforestation program in residential neighborhoods could add 1.2 billion trees, reducing population-weighted average summer temperatures by an additional 0.38 ± 0.01⁰C. Relative to the current status quo, this increase in the cooling benefits of trees would reduce annual heat-related mortality by an additional 464 ± 89 people, annual heat-related morbidity by 80,785 ± 6110 cases, and annual electricity consumption by 4.3 ± 0.2 TWhr, while increasing annual carbon sequestration in trees by 23.7 ± 1.2 MtCO2e and decreasing annual electricity-related GHG emissions by 2.1 ± 0.2 MtCO2e. The total economic value of these benefits, including the value of carbon sequestration and avoided emissions, would be USD 9.6 ± 0.5 billion, although in many neighborhoods the cost of increased tree cover exceeds these benefits. The exception is neighborhoods that currently have lower tree cover, especially those that are majority POC, as these neighborhoods have a much higher return-on-investment from tree planting.

Rapidly reducing greenhouse gas emissions is critical to limit global warming below 2°C. However, the magnitude and timing of beneficial effects of emissions reductions on labor productivity and the size of those effects relative to the costs of emissions reductions remain understudied. Here we use reanalysis data and climate model simulations to estimate current and future potential global labor losses associated with heat and air pollution exposure. We also examine the timing of benefits for avoided air pollution and heat exposure under a mitigation scenario consistent with limiting warming to around 2°C. Under the 2°C scenario compared to a higher emissions scenario representative of current mitigation policies, we find large, near-term benefits for countries with relatively poor air quality, such as China, India, and Nigeria. Avoided global labor productivity losses associated with air pollution exceed $600 billion/year within a decade, and peak by mid-century at about $860 billion/year. By contrast, avoided productivity losses associated with heat exposure do not exceed $500 billion/year until mid-century, but continue to grow for the remainder of the century. Over all time horizons, the avoided global labor productivity losses from aggressive emissions reductions exceed estimated additional energy investments needed to limit warming to ~2°C.