Mauna Loa Observatory

The weather measurements made here are so sensitive that when the observatory was built in 1956 scientists asked the national park to ban stoves at the summit cabin, fearing those emissions 6 miles away would throw off their readings. The park didn't, but the observatory managed to adjust. It has continuously recorded carbon dioxide (CO₂) and other human-produced greenhouse gas levels ever since, defining much of our understanding of global climate change. Tours of the facility are by appointment only.