Hawaii's Mauna Loa Observatory (MLO) is one of the world's leading scientific stations for monitoring the atmosphere. For more than fifty years, beginning with atmospheric chemist Charles Keeling's readings of carbon dioxide levels in the atmosphere, MLO has provided climate scientists a continuous record of the atmosphere's increasing concentration of carbon dioxide--and sparked the international debate over global warming. Hawai'i's Mauna Loa Observatory tells the story of the men and women who made these and many other measurements near the summit of the world's largest mountain. Botanist Archibald Menzies, who trekked up Mauna Loa's rough, lava-encrusted slopes in 1794, was the first to make scientific measurements from the summit. In the winter of 1840, the US Exploring Expedition spent a grueling three weeks at the edge of the summit crater. Their scientific achievements remained unsurpassed for more than a century and anticipated the research that was begun in 1951, when a primitive weather station was built atop the mountain. Serious research began in 1956 when the first building of the present observatory was erected a few thousand feet below the summit. Recollections of past and present MLO staff detail the historic beginning of carbon-dioxide measurements and many exciting discoveries and near disasters at the remote observatory in this colorful account of the evolution of MLO into a world-class facility. Today more than a hundred experiments are carried out at MLO, including precise measurements of the ozone layer, the sun's ultraviolet, the dust and air pollution drifting across the Pacific from Asia, and a wide assortment of gases in the atmosphere. These and other measurements have provided ground truthing for satellite-borne sensors and led to major scientific findings, some of which have influenced public policy decisions. Hawai'i's Mauna Loa Observatory should be read by atmospheric science students to gain an appreciation for the enormous effort required to generate high quality data. Much more than a strict scientific biography of Mauna Loa, this work will also be appreciated by anyone interested in a highly accessible history of the human side of atmospheric observations at a remote, high-altitude observatory.