Colonization of Antarctica refers to establishment of civilian settlements in Antarctica having humans, including families, living on the continent of Antarctica. Currently, the continent hosts only two civilian settlements, the Argentinian-administered Esperanza Base and Chilean-administered Villa Las Estrellas, as well as about 70 scientific and military bases with a transient population of scientists and support staff. Antarctica is the only continent on Earth without indigenous human inhabitants, despite its proximity to Argentina and Chile at the Antarctic Peninsula. At present scientists and staff from 30 countries live on about 70 bases (40 year-round and 30 summer-only), with an approximate population of 4,000 in summer and 1,000 in winter. There have been at least eleven human births in Antarctica, starting with one in 1978 at an Argentine settlement, with seven more at that base and three at a Chilean settlement. The Antarctic Treaty System, a series of international agreements, presently limit claims and activities on Antarctica. It would need to be modified or abandoned before additional large-scale colonization (coincident with national territorial claims) could legally occur, in particular with respect to the Protocol on Environmental Protection to the Antarctic Treaty. Past colonization speculation An idea common in the 1950s was to have Antarctic cities enclosed under glass domes. Power and temperature regulation of the domes would come from atomic driven generators outside of these domes. While the Soviets used radioisotope thermal generators in some of their remote Arctic and Antarctic locations, the Americans experimented with nuclear fission, building on their Army nuclear power plant program. The PM-3A nuclear power reactor at McMurdo Station was plagued with reliability issues (achieving an availability factor of only 74%) and was eventually deemed a pollution hazard and consequently shut down and dismantled. Buckminster Fuller, the developer of the geodesic dome, had raised the possibility of Antarctic domed cities that would allow a controlled climate and buildings erected under the dome. His first specific published proposal for a domed city in 1965 discussed the Antarctic as a likely first location for such a project. The second base at Amundsen–Scott South Pole Station (operated 1975-2003) resembles a reduced version of this idea; it is large enough to cover only a few scientific buildings. In 1971, a team led by German architect Frei Otto made a feasibility study for an air-supported city dome two kilometers across that could house 40,000 residents. Some authors have recently tried to update