on hydropower for about half their electricity. Observatory Located at , the Mount Chacaltaya Laboratory began as a weather station in 1942. It is an important site for gamma ray research and was the site in the 1940s of the first observations of pions. The Chacaltaya (Astrophysical) Observatory belongs to the Universidad Mayor de San Andrés and it is operated in collaboration with other universities worldwide. It hosts a cosmic ray research group, and since 2011 the Chacaltaya Global Atmosphere Watch (GAW) station. The GAW station is one of the few monitoring sites of Essential Climate Variables (meteorological variables, aerosols, and greenhouse gases) in the Southern Hemisphere. Climate See also List of highest astronomical observatories Retreat of glaciers since 1850 References External links GAW station Chacaltaya Glass Chamber Pyramid of the High Altitude Pathology Institute (Clinica IPPA) Apex 3 medical research expedition Chacaltaya Cosmic Rays observatory Glaciers of Bolivia Ski areas and resorts in Bolivia Astronomical observatories in Bolivia Mountains of La Paz Department (Bolivia) Tourist attractions in La Paz Department (Bolivia) Five-thousanders of the Andes