Mauna Loa, Hawaii, United States (Google Maps ⧉, OpenStreetMap ⧉)

"…Carbon dioxide levels from Mauna Loa and the Law Dome ice cores in Antarctica."

"*  South Pole, Mauna Loa: C. D. Keeling, T. P. Whorf, and the Carbon Dioxide Research Group, Scripps Institute of Oceanography (SIO), University of California, La Jolla, CA 92093, U.S.A."