Climate change exacerbates environmental risks such as intensifying extreme precipitation and heat events. Urban design, in turn, can further amplify these background climate stressors through the well-known urban heat island and rainfall effects, which are largely controlled by the local dominance of impervious land covers, surface roughness, and lack of mature tree canopy. While the extent to which present-day exposures and outcomes related to these climate-exacerbated environmental risks in urban areas can be linked to historical policies has received recent attention (Mujahid et al. 2021;Lane et al. 2022;Swope et al. 2022), causal inference within observed correlative associations has yet to be established. Here, we use a boundary design to estimate the persistent, causal effects of redlining on present-day exposure to climate change-exacerbated environmental risks in six large U.S. cities. Properties in areas assigned a lower-credit grade by the Home Owners' Loan Corporation in the 1930s have 3% higher exposure to flood risk and a 0.07 • F higher air temperature today compared to similar properties in higher-graded areas. We show that these differences are driven by lower tree canopy coverage and ground surface perviousness (important measures of environmental capital) in lower-graded areas. Our findings establish, for the first time, that the long-lasting effects of historical urban planning policies can be causally linked to present-day unequal exposures to climate risks.

We provide new evidence that policies implemented nearly a century ago have significant causal effects on the exposure of 9 urban communities in the U.S. to climate-related risks. Using a boundary design, we show that redlining, a discriminatory federal housing policy pursued in the 1930s and outlawed in the 1960s, has resulted in persistent inequality in climate risk exposure. Locations in neighborhoods assigned lower credit grades have significantly higher exposure to flooding and higher air temperatures than comparable locations with higher grades. We attribute these disparities to lower measures of environmental capital, specifically tree coverage and ground surface perviousness, in these neighborhoods. Our findings underscore the ongoing causal effects of historical housing policies on present-day exposure to climate risks, and highlight the need to address the legacies of past policies in adapting to future climate risks.

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