Climate change increases emergency department visits for heat-related illness in the United States

Rates of heat-related illness emergency department (HRI-ED) visits are rising in the United States, but the contribution of human-caused climate change to this trend is unknown. This climate impact attribution study quantifies the contribution of human-caused climate change to the rate of HRI-ED visits across the United States over the 2018–2025 April-October period. The study first develops a statistical model relating daily rates of HRI-ED visits to daily temperature observations, then employs a daily counterfactual temperature time series to estimate what HRI-ED visit rates would have been in the absence of climate change. We estimate that nationally, climate change contributed an average of 27.1% to the total rate of warm season HRI-ED visits over this time period. While the largest average absolute increases due to climate change were estimated in regions with warmer climates, proportional contributions varied substantially across regions. The contribution of climate change to elevated HRI-ED visits rates during recent heat waves in the Pacific Northwest and Atlantic Seaboard and to counts of HRI-ED visits in California is also quantified. We estimate that the rate of HRI-ED visits – and total visit count for the California event – would have been 20–30% lower without the influence of climate change on daily high temperatures. These results make clear that human-caused climate change is having a substantial influence on the rate of HRI-ED visits throughout the United States. With global temperatures and extreme heat events rising, this work could help inform measures to mitigate risks to public health.