DK Science: Climate
Every part of Earth has its own climate – the typical pattern of weather over a long period of time. An area’s climate is affected by its latitude (its distance north or south of the Equator), its height above sea level, and how far it is from the sea. In many parts of the world, conditions also vary with the SEASONS. A region’s climate affects the types of plants and animals found there, and the kind of homes that the local people build.
Dense tropical rainforests grow in a belt north and south of the Equator, where the climate is hot and wet. Temperatures vary between just 24–27°C (75–82°F), and it rains nearly every day. The subtropics on either side of the tropics are cooler. Some parts of the subtropics have an annual dry season and rainy season.
Earth’s landmasses can be divided into nine major climate zones, based on their usual temperature, rainfall, and the type of vegetation that grows there. Tropical areas are hot all year round, while polar regions and the tops of high mountains are always cold. Temperate zones in between the poles and the tropics, such as temperate forests and Mediterranean regions, have moderate, but seasonally changing, climates. Deserts are dry, receiving less than 25 cm (9 in) of rainfall every year.
Earth’s curving surface means that different regions receive different amounts of heat from the Sun. The midday Sun is directly overhead at the Equator, so the tropics are always hot. The Sun is low in the sky at the poles. Its rays are also spread over a wider area, and have further to travel through the atmosphere, so the poles are always cold.
The thin air high on mountains cannot absorb as much of the Sun’s heat as the air at sea level. The temperature therefore drops about 1°C (2°F) for every 150 m (500 ft) you climb. This results in various climate zones at different heights on mountains, each with its own characteristic vegetation. The snowline is at sea level near the poles and up to 5,000 m (16,500 ft) near the Equator.
The Sun shines on a turquoise sea in Provence, France, where the summers are hot and dry. Regions near coasts are usually wetter and milder than those inland. The sea absorbs the Suns heat more slowly than the land, but also releases heat more gradually. This gives coastal areas cooler summers and warm winters. Moist ocean winds blowing inshore bring rain, and help to cool coastal regions during the summer months.
Seasons are times of year characterized by certain weather conditions. In many parts of the world, temperatures and day length vary with the seasons. This affects plant growth, animal behaviour, and human life. The seasons occur because Earth is tilted on its axis (an imaginary line between the poles) as it travels around the Sun. Tropical regions have little seasonal variation: polar regions have the most.
Temperate lands located between the tropics and the polar regions experience four seasons: spring, summer, autumn, and winter. Many trees and plants in temperate regions reflect these seasonal changes. In spring, trees grow new leaves, which reach maturity in summer – the hottest season with the longest days. In autumn, trees shed their leaves in preparation for winter – the coldest season with the shortest days.