Climate of Alaska

Present climate of Alaska

Because of its wide latitudinal range and the proximity of the Pacific Ocean, Alaska has a variety of climatic areas. These range from rainforests in the Alexander Archipelago to tundra in Alaska’s far north.

Alaska’s climate is influenced by its mountain ranges and its proximity to the ocean. Statewide averages range from a low of -20°C (-4°F) in January to a high of 11°C (52°F) in July. North of the Brooks Range, Alaska has a cold, dry, polar climate with frequent winter blizzards. Temperatures on the coast are moderated somewhat by the Arctic Ocean. Central Alaska has a dry continental climate, with a large variation between summer and winter temperatures. For example, the town of Takotna in Alaska’s interior has an average low temperature of -27°C (-17°F) in January and an average high of 22°C (72°F) in July. Heat records have been broken in recent years, such as when the city of Anchorage, AK reported a temperature of 90°F (32.2°C) on July 4, 2019, and a weather station on Kodiak Island recorded a temperature of 67°F (19.4°C) on December 26, 2021.

Another climate area exists in the Alaskan southeast, south coast, and southwestern islands, and in west-central Alaska in the summer. These areas have moderate temperatures and high precipitation; average annual temperature is about 7°C (45°F). Some areas are home to lush rainforests and receive around 500 centimeters (200 inches) of rain a year.

The climate in west-central Alaska is influenced by a phenomenon that is unique in the United States: the seasonal presence of sea ice. In the winter when sea ice covers the Bering Sea, this area loses the moderating effect of open water and has a continental climate. When the sea ice melts in summer, the climate returns to a warmer, more humid maritime state.

Past climate of Alaska

This section covers the climate of Alaska through the Phanerozoic, from about 541 million years ago to the recent. For the climate on early Earth prior to 541 million years ago, see the Introduction to Climate section.

Paleozoic (541 to 252 million years ago)

Alaska is almost entirely composed of ancient terranes and volcanic island arcs that drifted together at different times during Earth’s history and had not assembled into anything resembling modern Alaska until the Jurassic. Most of these terranes appear to have experienced warm, wet climates, and geologists have concluded that they all originated in tropical areas of what is now the Pacific Ocean.

Alaska’s Cambrian- through Silurian-age rocks all formed on these tropical microcontinents. Devonian rocks are common in northern Alaska. These rocks include carbonate platforms, which are consistent with a low-latitude position and warm climate. Carboniferous and Permian rocks in Alaska originated on tropical terranes. Some contain lush, tropical floras that are completely dissimilar to those on the main part of the continent, a testament to their continued isolation in the ocean far from the North America, which had now become part of the supercontinent Pangaea. Carboniferous rocks in northern Alaska contain extensive carbonate platforms, which are indicative of a warm climate. Alaska’s Permian rocks are also indicative of a marine environment.

Mesozoic (252 to 66 million years ago)

Triassic to Jurassic (252 to 145 million years ago)

In the Triassic, around 220 million years ago, Pangaea, a supercontinent composed of nearly all the landmass on Earth, began breaking up into continents that would drift toward their modern-day positions. Island arcs formed close to what is now southern Alaska, where a very productive sea flooded the Triassic continental margin. Much of southern Alaska was assembled during the Jurassic as a series of island arcs and terranes collided with northern Alaska, which had now drifted into its current position and existed as a broad, flat shelf of shallow marine rocks. The Earth remained warm until worldwide temperatures began to dip again during the Late Jurassic, around 150 million years ago. 

Cretaceous (145 to 66 million years ago)

As a result of displacement due to continental rifting and seafloor spreading, sea level throughout the Cretaceous was much higher than it is today. Global temperatures during the Cretaceous were very warm, as much as 10°C (18°F) above those at present. There was likely little or no glacial ice anywhere on Earth, and temperatures were highest in lower latitudes. Shallow seaways spread over many of the continents, including South America, Africa, Eurasia, and North America. 

The Earth warmed near the beginning of the Cretaceous, and sea level rose. Even though Alaska was closer to the North Pole than it is at present, fossil vegetation indicates that its climate was very similar to that of western Oregon today. Lush swamps and forests occupied lowland areas; some of these swamps have become rich coal beds. The climate cooled again at the end of the Cretaceous, 65 million years ago. This cooling had the greatest impact on northern Alaska, where fossilized forests resemble those found near Anchorage today.

Cenozoic (66 million years ago to present)

Paleogene to Neogene (66 to 2.6 million years ago)

In the early Paleogene, the climate warmed once more. By around 50 million years ago, palm trees were growing in southern Alaska and the Alexander Archipelago. Alaska’s northern forests once again grew to resemble those of modern forests much farther south. Between 35 and 20 million years ago, however, the climate became cooler and drier, and deciduous trees such as oak, maple, and alder flourished.

Quaternary (2.6 million years ago to present)

Eventually, a sheet of sea ice formed over the Arctic, and ice sheets spread over northern Asia, Europe, and North America, signaling the start of the most recent ice age. Since 800,000 years ago, an equilibrium has been reached between warming and cooling, with the ice caps growing and retreating primarily due to the influence of astronomical forces (i.e., the combined gravitational effects of the Earth, Sun, moon, and planets).

During the last glacial maximum, ice reached as far south as the northern part of Washington State on the West Coast of North America. While ice covered some of Alaska, the ice sheet did not extend into central or northern Alaska because the local climate was very dry. However, an ice cap covered the Brooks Range. During periods of ice advance, Alaska was colder than it is today, with extensive mountain glaciers occurring throughout the state.

As in other parts of North America, Pleistocene megafauna roamed Alaska. The most iconic of these animals may have been the woolly mammoth (Mammuthus primigenius). The last woolly mammoths in Alaska (and in the United States) lived on St. Paul Island, a remote volcanic island located to the southwest of mainland Alaska; they survived there until about 5600 years ago.