Although Antarctica has no permanent residents, the population of scientists and support staff working in its research installations was estimated at 4,000 for the summer season and 1,000 for the winter season in 2005. Twenty-six countries helm Antarctic research stations.
Antarctica's harsh climate and long dark winters make it inhospitable for long-term colonization. The Antarctic Treaty allows 26 nations to conduct research on the continent. Many research stations are staffed only in the lighter summer months, and those that remain staffed year-round reduce personnel during the winter season. The United States maintains the largest population, followed by nearby Argentina and Chile. In addition to those included in population counts, another approximately 1,000 scientists work aboard ships in the waters surrounding Antarctica, and temporary camps and research stations are common on the continent in the summer.