Before You ReadThink about the weather during a year in your town or city. Write a sentence that tells if your home area is mostly cool or warm. Then read the lesson to learn about climates.
-!).�� )DEA
The climate of a region is often defi ned by annual temperatures and precipitation amounts.
What You’ll Learn" the characteristics of a
mediterranean climate and a highland climate
" ways that human activities can affect the climate
3TUDY�#OACH
Outline Make an outline to organize the information in this lesson. The numbered headings should be the main points in the outline. Under each heading, list the details or examples that help explain the main idea.
A World of Many ClimatesYou live in a world of different climates—from hot and
dry desert areas, to warm and wet rainforest regions, to frigid cold tundra at the poles. The climate of different regions affects all of the organisms living there
What is climate?Climate is the long-term average of the weather patterns
of an area. Climate includes temperature, winds, and precipitation of a long period of time.
What are climate regions?The different climates of Earth are classifi ed into climate
regions. One popular classifi cation system uses temperature, precipitation, and vegetation as characteristics to describe the climate of a region.
The main climate regions of Earth include: • cold polar tundra, • dry desert, • mediterranean, • humid subtropical, • highland, • humid continental, and• marine.
Read to Learn
1. Identify What three characteristics are used to classify climate regions?
Grade Six Science Content Standard. 4.d. Students know convection currents distribute heat in the atmosphere and oceans.
140 Chapter 11 Weather and Climate Reading Essentials
What are California’s climates?Most of California has mediterranean and highland
climates. A mediterranean (me dih tur RAY nee uhn) climate is characterized by mild, wet winters and hot, dry summers. Mediterranean climates usually occur on the western side of a continent. Because mediterranean climates are often extremely dry, summer fi res often occur in those regions. A highland climate is characterized by cool-to-cold temperatures and occurs in the mountains and on high plateaus.
Climate ControlsUneven heating of Earth’s surface by the Sun results in
air currents and ocean currents that infl uence the different climate regions. Other factors, such as the latitude and altitude of a location, the distance from a large body of water, and the presence or absence of mountain barriers, also affect the climate experienced in different areas. These factors are called climate controls. Some of these factors, such as latitude and mountain barriers are unchanging. Other factors, such as winds and ocean currents, can vary according to seasons.
.%§C
+%§C
(%§C
%§
(%§H
+%§H
.%§HIgde^XVa�LZiIgde^XVa�LZi���9gn
Igde^XVaHZb^Vg^Y6g^Y
9gn
BVg^cZ�LZhi�8dVhiBZY^iZggVcZVc=jb^Y�HjWigde^XVa
B^aY
IjcYgV>XZXVe
EdaVg
LVgb�HjbbZg8dda�HjbbZgHjWVgXi^X
8dci^cZciVa=^\]aVcYhJeaVcYh
=^\]�:aZkVi^dc
.%§C
+%§C
(%§C
%§
(%§H
+%§H
.%§H
:Vgi]¼h�8a^bViZ�GZ\^dch
Picture This 2. Classify Is your region
composed of one climate or a mixture of climates?
C Compare Make a Venn-diagram Foldable. Record what you learn about mediterranean and highland climates as they relate to California under the appropriate tabs.
Mediterranean
Climate
HighlandClimate
Both
Reading Essentials Chapter 11 Weather and Climate 141
What do you need to know about latitude?Recall that areas close to the equator receive more solar
radiation than areas located further north or south. Since more solar radiation is received in areas near the equator, these areas have warmer climates than those regions at higher latitudes.
How does the distribution of land and water affect climate?
The distribution of land and water has an important infl uence on climate. Recall that water can absorb or lose large amounts of heat without changing temperature. Land does not have this characteristic. Land surfaces heat and cool rapidly. Ocean surfaces heat and cool slowly. As a result, the climate of locations near an ocean is affected as illustrated in the map below. For example, San Francisco and Wichita are cities located at the same latitude. However, they do not have the same climates. San Francisco is warmer in winter and cooler in summer because it is near the ocean.
3. Explain Why do areas near the equator have warmer climates?
How do ocean currents affect climate?Ocean currents help to redistribute the Sun’s energy on
Earth. Ocean surface water near the equator receives more solar radiation than surface water at high latitudes. Large ocean currents that move water away from the equator, such as the Gulf Stream, carry heat to higher latitudes. Ocean currents moving toward lower latitudes, such as the California Current, replace the warm water from the lower latitudes with cold water from higher latitudes.
San Francisco37ºNJan. 9ºCJuly 16ºC
Wichita37ºNJan. –1ºCJuly 27ºC
Pacific Ocean
San Francisco’s climate is affected by the nearby ocean.
The climate along the northwest coast of the United States is affected by the ocean.
Atlantic Ocean
C A N A D A
U N I T E D S T A T E S
Average Yearly
Precipitation (cm)
Over 150100–14950–9925–49Under 25
Picture This 4. Explain Study the map.
Why is San Francisco warmer in winter and cooler in summer than Wichita?
How do the Gulf Stream and California Current affect climate?
This redistribution of heat by ocean currents can be seen when comparing the average winter temperatures of Great Britain to those of Labrador, Canada. These two locations are found at the same latitude. However, due to the infl uence of the warm Gulf Stream, the average winter temperature in Great Britain is 15°C–20°C warmer than that of Labrador. The cold Labrador Current runs along the coast of Labrador, keeping winter temperatures low.
The California Current is a cold-water current that begins in the North Pacifi c Ocean and fl ows past the coast of California. The water temperature of the California current remains stable year-round. This helps keep temperatures along the coast from rising too high in the summer and from dipping too low in the winter.
What are prevailing winds?A prevailing wind is a wind that blows most often across
a particular area. Prevailing winds signifi cantly infl uence the climate of a location. Most of the United States, including California, is affected by the prevailing westerlies. In California, the infl uence of the westerlies results in rain during the winter months.
What effect do humans have on climate?Some scientists believe that human activities can affect the
climate of our planet. Recall that the burning of fossil fuels releases greenhouse gases. An increase in the concentration of greenhouse gases could lead to global warming. If the average surface temperature of Earth increases, scientists hypothesize that global climate changes could occur.
Describing ClimateClimate is usually described in terms of the average weather
conditions of an area over a long period of time. Conditions such as temperature, precipitation, and winds are taken into account when describing a climate. Most of California has either a mediterranean climate or a highland climate. Factors that infl uence climate include latitude, altitude, distance from a large body of water, and presence or absence of mountain barriers. The climate of the coastal areas of California is infl uenced by the California Current. Altitude or mountain barriers may infl uence climate in inland areas of California.
5. Name one human activity that might affect climate.
