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NATS 101
Section 4: Lecture 32
Global Climate
Classifying the global climate and
Earth’s climate record is probably not as
exciting as learning about hurricanes or
tornadoes, but it important prelude
before we get to global warming, the
final topic of the course.
Some reasons why understanding
global climate is important
The type of climate in an area is a control on an area’s ecosystem.
Plant and animal species are specifically adapted, physically and
behaviorally, to climate.
Climate affects how human civilization has evolved and adapted to
cope in various environments. For example:
Agriculture: types of crops and domesticated animals
Water supply
Types of dwellings and structures built
Clothing
Social structures, like governments and religions
Climate patterns may change due to anthropogenic (human-related)
activities—and this is probably already happening. More on that
later…
Survey question: Which of the following statement best represents
your position with respect to the potential impact of weather and
climate on our modern American civilization?
A) Our civilization is totally resilient to weather and climate.
B) Our civilization is susceptible to disruption from extreme weather
and climate events from time to time, for example hurricanes and
droughts, but these events are localized and affect a small
portion of the population.
C) Our civilization, as a whole, is highly vulnerable to weather and
climate. Changes in weather and climate have the potential to
cause widespread societal disruption, and, in the most extreme,
dramatically alter or destroy our way of life.
Ancient civilizations that
succumbed to climate change
ANASAZI
Four Corners Region
Southwest U.S.
ARID DESERT CLIMATE
MAYA
Yucatan Peninsula
Mexico
TROPICAL WET-DRY CLIMATE
PROLONGED DROUGHT PERIODS LIKELY LEAD TO FAMINE AND WAR,
AND THESE ANCIENT CIVILIZATIONS WENT INTO DECLINE.
We’ve already discussed many of the
controls on global climate
in previous lectures.
I’ll briefly review those and then
describe a formal global climate
classification system.
Climate control #1: Latitude
What it does:
Controls the intensity of incoming
solar radiation.
Effects
January Average Temperature
Temperatures decrease with
increasing latitude. Effect is more
pronounced in wintertime.
Largest annual changes occur at
higher latitudes.
Temperature does not change
much in the low-latitude tropics
Climate Control #2:
Land-Sea distribution
SIBERIA
-60 °F
January
What it does:
Water has a higher heat
capacity than land, so it
heats and cools more
slowly than the
surrounding land mass
Effect on climate:
SIBERIA
50 °F
July
Maximum Temperature
Locations closer to a
large water body will:
1. Have less of a
seasonal temperature
range.
2. Have a later
occurrence of annual
maximum and
minimum temperature.
Climate control #3:
Ocean Currents
What they do:
Giant convective circulations
(gyres) transport heat from
equator to pole.
The warm side of a gyre is
typically along the east coast
of a continent.
Canary
The cold side of a gyre is
typically along the west coast
of a continent.
Effect on climate
Climates on east and west
coasts of continents margins
are respectively modulated by
the presence of warm and
cold ocean currents.
Climate control #4: the general circulation
What it does:
Governs the locations
where air converges or
diverges on a global
scale.
Effect on climate
It is the primary control
on the global distribution
of rainfall.
SAHEL
SAHARA DESERT
SAHARA DESERT
SAHEL
CONGO
RAIN FOREST
CONGO
KALAHARI
DESERT
SARENGETI
(UNC Charlotte)
KALAHARI DESERT
Climate control #5: Terrain
What it does:
Mountain valley circulations.
Monsoons
Orographic uplift
Effect on climate
Example of rain shadow effect
All of these factors can be
potentially very significant
controls on the precipitation
occurring at a regional scale.
As we discussed earlier, these
factors are really important for
understanding Arizona’s
climate!
Köppen climate classification system
Developed a climate classification
system based on common vegetation
types observed throughout the world.
Goal was to explain climate in areas
that had few or no station
observations.
Basic Types
Wladimir Köppen
German climatologist
A = Tropical moist
B = Dry
C = Moist temperate
D = Moist cold
E = Polar
H = Highland
Notations for subtypes derive from
German.
Climates of the world in Köppen system
Rest of the lecture is taking the “tour” of this map…
Type A: Moist Tropical Climates
Characteristics
Year-round warm temperatures (above an average of 64 °F)
Abundant rainfall (about 60 inches a year)
Wet and dry seasons controlled by the position of the ITCZ.
Where located
Equator to about 15 – 25° latitude.
Subtypes
Af = Tropical wet
Am = Tropical monsoon
Aw = Tropical wet and dry
Tropical Wet (Af)
These regions are tropical rainforests.
Typically near the equator.
Wettest time of the year is typically during
the equinoxes when the ITCZ is nearest to
the equator.
Temperature hardly varies through the
year.
Tropical monsoon (Am) climates similar,
but have a bit more variation in rainfall.
Example Regions:
Tropical Wet (Af) Climates
AMAZON
\
CONGO
INDONESIA
Tropical Wet-Dry
(Aw)
About 5 - 20° latitude, on the periphery of
the ITCZ.
Strong annual variation in rainfall,
controlled by ITCZ position
Summer wet season
Winter dry season
Savannahs, or large grasslands with
scattered trees, like the Sarengeti in
Africa.
Example Regions:
Tropical Wet-Dry (Aw) Climates
SAHEL
BRAZILIAN
HIGHLANDS
\
SARENGETI
Type B: Dry Climates
Characteristics
Low precipitation most of the year (less than 20 inches).
Located under the subtropical high most of the time.
Favored on the west side of continents because of cold sea surface
temps.
Where located
About 20 - 40° latitude
Subtypes
BW = Arid Desert
BS = Semi-arid or steppe
Arid desert (BW)
Receives less than 13 inches of rain
per year
Hottest temperatures on Earth (e.g.
greater than 120 °F)
Plants that live in these areas are
xerophytes, capable of living long
periods without rain.
THIS IS THE CLIMATE FOR MOST OF
ARIZONA
Example Regions:
Arid Desert (BW) Climates
GOBI DESERT
SONORAN
DESERT
SAHARA
ARABIAN
DESERT
ATACAMA
DESERT
\
KALAHARI
DESERT
AUSTRALIAN
DESERT
The driest spot on Earth…
where is this??
Semi-arid or Steppe
(BS)
Receive about 8 to 16 inches of rainfall.
Short grasses and scattered low bushes
and trees.
Can get cold in the winter, if in the midlatitudes.
Areas typically are good for grazing
animals.
In the tropics, typically the transition zone
from tropical-wet dry to arid desert.
Example Regions:
(Mid-latitude) Steppe (BS) Climates
CENTRAL
ASIA
GREAT
PLAINS
PAMPAS
\
Type C: Moist Temperate Climates
Characteristics
Humid with mild winters
About 20 to 40 inches of precipitation per year
Very different subtypes depending on continental position.
Where located
About 25 - 40° latitude
Subtypes
Cfa= Humid subtropical
Cfg = West coast marine
Cs = Mediterranean
Humid
Subtropical (Cfa)
Typically along east coasts of
continents, on the western side of the
subtropical ridge.
Wet all year round, but slightly more
rain in the summer.
Hot, muggy summers
Supports thick forests or agriculture.
Example Regions:
Humid Subtropical (Cfa) Climate
SOUTHEAST
CHINA AND JAPAN
SOUTHEAST
U.S.
EASTERN
ARGENTINA
AND
URUGUAY
\
NORTHEAST
SOUTH AFRICA
EASTERN
AUSTRALIA
West coast marine
(Cfb)
Located at 40 – 60° latitude
Rain throughout the year, especially
in winter. More so if on the
windward side of mountain range.
Receive rain from mid-latitude
cyclones hitting west coasts.
Proximity to water moderates the
climate
Example Regions:
West Coast Marine (Cfb) Climate
NORTHERN
EUROPE
PACIFIC
NORTHWEST
SOUTHERN
CHILE
\
NEW ZEALAND
Mediterranean (Cs)
Located equatorward of the west
coast marine climates (30 - 40°
latitude)
Under the subsiding branch of the
eastern side of the subtropical high
in summer, so hot and dry then.
Wet, mild winters.
Short scrubby vegetation with a few
trees.
Good climate for winemaking!
Example Regions:
Mediterranean (Cs) Climate
MEDITERRANEAN
CALIFORNIA
CENTRAL
CHILE
\
CAPE TOWN
AREA
SOUTHWEST
AUSTRALIA
Mediterranean Climate and
the Roman Empire
Relatively similar and
agriculturally productive
climate conditions exist
throughout much of the
Mediterranean.
Same crops that grew in
one place would also grow
in a another place.
FACILITATING FACTOR IN
THE EXPANSION OF THE
ROMAN EMPIRE AND
DEVELOPMENT OF
WESTERN CIVILIZATION!
Type D: Moist Cold Climates
Characteristics
Warm to cool summers
Cold winters with snow
Large seasonal temperature range
About 30 - 40 inches of precipitation per year.
Where located
About 25 - 70° latitude
Subtypes
Dfa and Dfb = Humid continental
Dfc = Subpolar
Humid continental
(Dfa and Dfb)
Typically more toward the eastern side
of a continent, poleward of moist
subtropical areas.
Regular precipitation throughout the
year.
Summer precipitation maximum.
Summers can be sometimes hot.
Favorable for deciduous forests and
agriculture
Example Regions:
Moist cold (Df) Climate
EASTERN EUROPE
AND SOUTHEAST
RUSSIA
MIDWEST AND
NORTHEAST
U.S.
\
NORTHEAST
ASIA
Subpolar or
Boreal (Df)
Very cold winters
Fairly low precipitation (less than 20
inches per year)
Typically supports large evergreen
boreal forests, or taiga.
Example Regions:
Boreal Forests (Df)
NORTHERN
CANADA AND
ALASKA
\
NORTHERN
SCANDANAVIA
AND SIBERIA
Type E: Polar
Climates
Characteristics
Cold temperatures year
round.
Tundra, permafrost, or ice
cap.
Very little precipitation.
Where located
Poleward of boreal forest
THESE REGIONS ARE CHANGING
RAPIDLY DUE TO RECENT GLOBAL
WARMING.
Type H: Highland Climates
Climate changes experienced with increasing altitude. Farther
up, the typically more “polar” the climate gets.
THESE REGIONS ARE ALSO CHANGING RAPIDLY DUE TO THE
RECENT GLOBAL WARMING—PARTICULARLY MOUNTAIN
GLACIERS.
Example Regions:
Highland Climates (H)
ROCKY
MOUNTAINS
CENTRAL
ASIA AND
TIBET
ANDEAN
ALTIPLANO
WE’LL SEE WHAT HAS HAPPENED TO MOUNTAIN GLACIERS IN
THESE PLACES LATER…
Summary of Lecture 32
The major controls on climate are latitude, land-sea distribution, ocean
currents, the general circulation, and terrain.
Climate is classified by the Köppen system.
TROPICAL MOIST (A): Either rainforest near the equator or savannah farther
polward. Precipitation influenced by the ITCZ.
DRY (B): Deserts typically located under the subtropical ridge and/or near the
west coast of continents. Steppes are grassland transition zones.
MOIST TEMPERATE (C): Specific subtype depends on continental position
(east vs. west). Moist subtropical on eastern side, west coast marine and
Mediterranean on the western side.
MOIST COLD (D): Poleward of moist temperate climates, with large seasonal
shifts in temperature. Includes boreal forest.
POLAR (E): Tundra, permafrost, or ice cap.
HIGHLAND (H): Colder climate due to higher elevation.
Reading Assignment and
Review Questions
Reading
Chapter 16 (last Chapter to be covered)
Chapter 17 Questions
Questions for Review: 1,2,3,4,5,7,8,9,10,11,12,13,19 (8th ed.)
1,2,3,4,5,6,7,8,9,10,11,12,13,14,20 (9th ed.)
Questions for Thought: 2,3,5,6
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