Science High School Reviewer | Grade 4 Science | Earth Science | Weather and Climate | Lesson 24: Climate

What is climate?
The weather where you live may change from
day to day. Yet you can predict what the weather
will be like each season. The pattern of seasonal
weather that happens year after year is called
climate (KLYE•mit).
Climate is not the same everywhere on Earth.
The city of Phoenix is in the southwest United
States. The climate there is warm and dry all year.
Snow and rain rarely fall. Seattle is in the northwest
United States. There the climate is cool and wet.
Farmers depend on climate to grow their
crops. Some crops grow well in cool climates
with steady rain. Other crops need dry climates.
Still others need warm, humid climates.

Climate Regions
Think of climate as the average
weather in a certain place for a
long period of time. It has similar
patterns of temperature, humidity,
precipitation, and wind. We can call
such an area a climate region.
Polar regions have cold climates
with low precipitation. Tropical
regions are near the equator.
There, the climate is warm, humid,
and rainy. Temperate regions lie
between polar and tropical regions.
Temperate climates often have
four seasons. Some have just two
seasons—a dry one and a rainy one.
Still other regions are dry or cool.

What determines climate?
Several things affect a climate
region over time. These include
latitude, winds, and currents.
Latitude
The thin lines that run east and
west across some maps are lines of
latitude. Latitude is a measure of
how far a place is from the equator.
The equator’s latitude is set at zero
degrees. Latitude increases as you
move north or south from there. The
highest latitude is at the North and
South Poles. Both are 90 degrees.
Climates near the equator are
warm and rainy. Between the
equator and the poles, the climate is
mild or temperate. Near the poles,
the climate is cold all year.

Global Winds
Temperature differences between
latitudes cause global winds. These
are winds that move air between the
equator and poles. Warm air near
the equator rises and moves toward
the poles. Cold air near the poles
sinks and moves toward the equator.
Ocean Currents
A current is a directed flow of a
gas or a liquid. Some ocean currents
move warm water from the equator
to the poles. Others move cold water
from the poles toward the equator.
There are also currents that move
along lines of latitude. Together,
these currents form circular patterns
in the oceans.

Distance from Water
Do you like to swim at the beach
in summer? You may have noticed
that the water stays cool even on the
hottest days. That is because water
heats up more slowly than land
does. Water cools more slowly, too.
Remember that more than 70
percent of Earth’s surface is covered
by water. Land and water heat
and cool at different rates. These
differences affect the air temperature
and precipitation nearby.
Climates near lakes and oceans
are cloudier and rainier than
regions farther inland. Summers
are cooler. Winters are warmer.
Nearness to water reduces
temperature extremes. It also
increases moisture in the air.

How do mountains
affect climate?
Latitude, water,and winds are not
the only factors that affect climate.
Mountains also have an effect.
Altitude
Climate at the base of a mountain
is always warmer than at its peak.
The higher the altitude, the lower
the air temperature. Altitude is a
measure of the height of a place
above sea level.
What happens when an air mass
meets a mountain? The air rises up
the side of the mountain. As the
altitude gets higher, temperature
gets cooler. Water vapor in the air
condenses into clouds.

Clouds and Precipitation
As a cloud moves up a mountain,
its water droplets get heavy.
Precipitation falls. By the time the
air mass passes over the mountain,
the air is dry. For this reason, the
climate on one side of a mountain
tends to be wet. The climate on
the other side is often dry.