In parts of the Arctic are found a variety of natural resources, but many known reserves are not exploited because of their inaccessibility. The arctic region of Russia, the most developed of all the arctic regions, is a vast storehouse of mineral wealth, including deposits of nickel, copper, coal, gold, uranium, tungsten, and diamonds. The North American Arctic yields uranium, copper, nickel, iron, natural gas, and oil. The arctic region of Europe (including W Russia) benefits from good overland links with southern areas and ship routes that are open throughout the year. The arctic regions of Asian Russia and North America depend on isolated overland routes, summertime ship routes, and air transportation. Transportation of oil by pipeline from arctic Alaska was highly controversial in the early 1970s, with strong opposition from environmentalists. Because of the extreme conditions of the Arctic, the delicate balance of nature, and the slowness of natural repairs, the protection and preservation of the Arctic have been major goals of conservationists, who fear irreparable damage to the natural environment from local temperature increases, the widespread use of machinery, the interference with wildlife migration, and oil spills. Global warming and the increasing reduction in the permanent ice cover on the Arctic Ocean has increased interest in the region's ocean resouces.