- Palin and some other mostly Republican politicians support drilling in the Arctic National Wildlife Refuge, which environmentalists oppose on the grounds that it could threaten the reserve's wildlife including caribou which require uninterrupted migration routes.

The 19.2 million acre (7.7 million hectare) refuge is home to 45 species of land and marine mammals, ranging in size from the pygmy shrew to the bowhead whale.

- The polar bear has become an icon of the debate on climate change. It has been listed as threatened under the US Endangered Species Act because US scientists concluded its icy Alaskan habitat was melting away. Palin opposes the listing on the grounds that it could hamper drilling.

- Palin has angered greens by questioning a human role in climate change. Like other far northern latitudes, climate change that most scientists link to fossil fuel emissions is seen having a greater and more rapid impact in Alaska than in warmer regions. In Alaska this is seen in shrinking glaciers and melting sea ice.

- The number of species found in an area tends to increase with proximity to the equator and decrease at more extreme latitudes. So while Alaska is in many ways pristine because it is remote and undeveloped, the loss of just a few species could be a serious blow to its biodiversity, with unforeseen consequences for the broader ecosystem.

- Alaska's environment remains healthy on a number of fronts. Unlike many other regions Alaska's commercial salmon fishing industry is regarded as sustainable and has been given a seal of approval by the Marine Stewardship Council which carefully scrutinizes fisheries.

(Sources: Reuters, US Fish and Wildlife Service, US National Park Service, Marine Stewardship Council; Editing by Deborah Zabarenko and Frances Kerry)