land area), and has the longest coastline, at . Asia is generally defined as comprising the eastern four-fifths of Eurasia. It is located to the east of the Suez Canal and the Ural Mountains, and south of the Caucasus Mountains (or the Kuma–Manych Depression) and the Caspian and Black Seas. It is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean and on the north by the Arctic Ocean. Asia is subdivided into 49 countries, five of them (Georgia, Azerbaijan, Russia, Kazakhstan and Turkey) are transcontinental countries lying partly in Europe. Geographically, Russia is partly in Asia, but is considered a European nation, both culturally and politically. The Gobi Desert is in Mongolia and the Arabian Desert stretches across much of the Middle East. The Yangtze River in China is the longest river in the continent. The Himalayas between Nepal and China is the tallest mountain range in the world. Tropical rainforests stretch across much of southern Asia and coniferous and deciduous forests lie farther north. Main regions There are various approaches to the regional division of Asia. The following subdivision into regions is used, among others, by the UN statistics agency UNSD. This division of Asia into regions by the United Nations is done solely for statistical reasons and does not imply any assumption about political or other affiliations of countries and territories. North Asia (Siberia) Central Asia (The 'stans) Western Asia (The Middle East or Near East and the Caucasus) South Asia (Indian subcontinent) East Asia (Far East) Southeast Asia (East Indies and Indochina) Climate Asia has extremely diverse climate features. Climates range from arctic and subarctic in Siberia to tropical in southern India and Southeast Asia. It is moist across southeast sections, and dry across much of the interior. Some of the largest daily temperature ranges on Earth occur in western sections of Asia. The monsoon circulation dominates across southern and eastern sections, due to the presence of the Himalayas forcing the formation of a thermal low which draws in moisture during the summer. Southwestern sections of the continent are hot. Siberia is one of the coldest places in the Northern Hemisphere, and can act as a source of arctic air masses for North America. The most active place on Earth for tropical cyclone activity lies northeast of the Philippines and south of Japan. Climate change Climate change is having major