Climate change has driven many organisms to shift their seasonal timing. Are humans also shifting their weather-related behaviors such as outdoor recreation? Here we show that peak attendance in US national parks experiencing climate change has shifted 4 days earlier since 1979. Of the nine parks experiencing significant increases in mean spring temperatures, seven also exhibit shifts in the timing of peak attendance. Of the 18 parks without significant temperature changes, only 3 exhibit attendance shifts. Our analysis suggests that humans are among the organisms shifting behavior in response to climate change.