The New Childrens Encyclopedia

ATMOSPHERE AND CLIMATE

53

WEATHER MACHINE

The Sun heats Earth’s surface, which warms the

atmosphere. Warm air rises, and cool air moves in

to replace it, causing winds. Warm air rises in the

tropics. Cool air moves in from the north and

south. Since Earth rotates on its axis, the winds

bend, creating huge swirling weather patterns.

Climate

The climate of a particular area is the different

patterns of weather and temperature over time.

Factors that influence climate include distance

from the equator and the sea, height above sea

level, and the surrounding landscape.

O
 For the last 50 years, the average

temperature on Earth has been increasing

by about^1 ⁄ 8 of a degree every ten years.

This is known as global warming

( p. 78–79).

O
 The change in temperature is causing

the glaciers and ice caps to melt.

FAST FACTS

SEASONS

The seasons are annual changes in

climate that occur in the northern and

southern hemispheres. There are four

seasons in temperate regions—spring,

summer, fall, and winter. They are due

to the differences in day length and the

strength of the sunlight as Earth orbits

the Sun. In many tropical and

subtropical areas, there are two

seasons—dry and wet.

 FULL TILT The seasons

occur since Earth tilts on its

axis as it orbits the Sun. This

has little effect at the equator,

where there is only one season.

Northern summer occurs

when the North Pole

tilts toward the Sun.

Sun

EARTH

Westerlies

Trade winds

Doldrums

Doldrums

Trade winds

Westerlies

 TEMPERATE

This zone experiences

changes in temperature

and rainfall during

the year, but none

are too extreme.

 POLAR The Arctic

and Antarctic polar

regions experience

freezing conditions

and little rainfall.

 TROPICAL This

zone lies north and

south of the equator

and is generally hot

and humid.

Dry air sinks over

Warm air rises at the world’s deserts.

the equator until

it hits the top of

the troposphere

and can rise

no farther.

The circulating air

patterns are called “cells.”

Southern summer

occurs when the

North Pole tilts

away from the Sun.

Very cold air sinks at
the poles and flows
outward, creating
winds called easterlies.

The area where the

trade winds die out is

known as the doldrums.

Sailing ships may

become stranded here.