Alaska had a population of 731,449 in the year 2013. In the interior of Alaska, there is a subarctic climate. Summers can reach up to 80 degrees Fahrenheit; winters can fall below -60 degrees Fahrenheit. Alaska has three million lakes, 29 volcanoes, and more than 100,000 glaciers. Mount McKinley, the tallest point in North America, is 20,320 feet tall. The ecosystem consists largely of tundra covering mountain ranges and coastal plains. The most commonly spoken language in Alaska is English. About 50% of the people who live there are Christians.