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.
When the North Pole tilts towards the Sun, it is summer in the
northern hemisphere (the half of the Earth above the Equator). Six months
later, when the South Pole tilts towards the Sun, it is summer in the southern
hemisphere (the half of the Earth below the Equator).
