Japan has a temperate to subtropical climate with hot, humid summers and mild winters. The terrain is mostly mountainous. The main ethnic groups are Japanese (98.5%) and small populations of Koreans, Chinese, Ainu, and Okinawans. Religions practiced are both Shintoism and Buddhism, with many following both. The government is a parliamentary constitutional monarchy with the Prime Minister having most political power. Natural hazards include frequent earthquakes, tsunamis from quakes, seasonal typhoons, and active volcanoes.