North America, the third largest continent is spread over 24,346,000 sq km and is the northern of the two continents of the Western Hemisphere. North America includes all of the mainland and related offshore islands lying North of the Isthmus of Panama which connects it with South America. It has a variety of climate, from the dry, bitter cold of the Arctic to the steamy heat of the tropics. The interior of Greenland, always at subzero temperatures is permanently covered by an icecap,. The North American tundra, the vast treeless plain of the far north, has temperature rises above freezing for only a short period each summer. In the far south there are low-lying areas which are always hot and rainy.
Most of the rest of North America is cold in the winter and warm in the summer, with moderate precipitation. Some areas have mild winters and long, hot summers and others have harsh winters and short summers. North America extends to within 10° of latitude of both the equator and the North Pole, embraces every climatic zone, from tropical rain forest and savanna on the lowlands of Central America to areas of permanent ice cap in central Greenland. Subarctic and tundra climates prevail in N Canada and N Alaska, and desert and semiarid conditions are found in interior regions cut off by high mountains from rain-bearing westerly winds. Fortunately , a large part of the continent has temperate climates very favorable to human settlement and agriculture.
North America has the United States and Canada as two of the largest global emitters of the greenhouse gases that contribute to a warming climate. All ten of the "hotspot" categories can be found in this region, including changes such as polar warming in Alaska, coral reef bleaching in Florida, animal range shifts in California, glaciers melting in Montana, and marsh loss in the Chesapeake Bay. This higher density of early warning signs in the US and Canada is also because these regions have more readily accessible climatic data and more means and programs to monitor and study environmental change.