Using daily data for the United States over the period 1980-2019, we estimate the impacts of temperature on ambient ozone concentrations, accounting for adaptation to climatic change. We find that even with adaptation, rises in temperature will steeply increase ozone levels by over 9 ppb on days above 25◦C. By mid-century, we calculate that 189 additional counties will be violating the air quality standards, with 33 million more residents exposed to unhealthy levels of ozone. Climate change will thus likely increase the costs of compliance with existing ambient ozone standards. In light of a recent EPA ruling that would effectively remove co-benefits of ozone precursor reductions from the cost-benefit analysis of those standards, they will be in peril, further threatening public health.