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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 animalsWater supplyTypes of dwellings and structures builtClothing 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

ANASAZIFour Corners Region

Southwest U.S.ARID DESERT CLIMATE

MAYAYucatan Peninsula

MexicoTROPICAL 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

January Average Temperature

What it does:

Controls the intensity of incoming solar radiation.

Effects

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

January

July

SIBERIASIBERIA-60 -60 °F°F

SIBERIASIBERIA50 50 °F°F

Maximum Temperature

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:

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.

The cold side of a gyre is typically along the west coast of a continent.

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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.

(UNC Charlotte)

SAHARA DESERTSAHARA DESERT

SAHELSAHEL

CONGOCONGORAIN FORESTRAIN FOREST

KALAHARI KALAHARI DESERTDESERT

SAR

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SAR

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ETI

CONGOCONGO

KALAHARI DESERTKALAHARI DESERT

SAHELSAHEL

SARENGETISARENGETI

SAHARA DESERTSAHARA DESERT

Climate control #5: Terrain

Example of rain shadow effect

What it does:

Mountain valley circulations.MonsoonsOrographic uplift

Effect on climate

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

Wladimir KöppenGerman climatologist

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

A = Tropical moistB = DryC = Moist temperateD = Moist coldE = PolarH = 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 wetAm = Tropical monsoonAw = 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

\

AMAZONAMAZON CONGOCONGO INDONESIAINDONESIA

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

\

BRAZILIAN BRAZILIAN HIGHLANDSHIGHLANDS

SAHELSAHEL

SARENGETISARENGETI

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 DesertBS = 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

\

ATACAMA ATACAMA DESERTDESERT

SAHARASAHARA

KALAHARIKALAHARI DESERTDESERT

SONORAN SONORAN DESERTDESERT

ARABIAN ARABIAN DESERTDESERT

GOBI DESERTGOBI DESERT

AUSTRALIAN AUSTRALIAN DESERTDESERT

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 mid-latitudes.

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

\

PAMPASPAMPAS

GREAT GREAT PLAINSPLAINS

CENTRAL CENTRAL ASIAASIA

Type C: Moist Temperate Climates

Characteristics

Humid with mild wintersAbout 20 to 40 inches of precipitation per yearVery different subtypes depending on continental position.

Where located

About 25 - 40° latitude

Subtypes

Cfa= Humid subtropicalCfg = West coast marineCs = 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

\

EASTERN EASTERN ARGENTINA ARGENTINA

AND AND URUGUAYURUGUAY

SOUTHEAST SOUTHEAST U.S.U.S.

SOUTHEAST SOUTHEAST CHINA AND CHINA AND

JAPANJAPAN

NORTHEAST NORTHEAST SOUTH AFRICASOUTH AFRICA

EASTERNEASTERNAUSTRALIAAUSTRALIA

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

\

SOUTHERN SOUTHERN CHILECHILE

PACIFIC PACIFIC NORTHWEST NORTHWEST

NORTHERN NORTHERN EUROPEEUROPE

NEW ZEALANDNEW 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

\

CENTRAL CENTRAL CHILECHILE

CALIFORNIA CALIFORNIA

MEDITERRANEANMEDITERRANEAN

CAPE TOWN CAPE TOWN AREAAREA

SOUTHWEST SOUTHWEST AUSTRALIAAUSTRALIA

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 snowLarge seasonal temperature rangeAbout 30 - 40 inches of precipitation per year.

Where located

About 25 - 70° latitude

Subtypes

Dfa and Dfb = Humid continentalDfc = 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

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NORTHEAST NORTHEAST ASIAASIA

MIDWEST AND MIDWEST AND NORTHEAST NORTHEAST

U.S. U.S.

EASTERN EUROPE EASTERN EUROPE AND SOUTHEAST AND SOUTHEAST

RUSSIARUSSIA

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 NORTHERN SCANDANAVIA SCANDANAVIA AND SIBERIAAND SIBERIA

NORTHERN NORTHERN CANADA AND CANADA AND

ALASKAALASKA

Type E: Polar Climates

Characteristics

Cold temperatures year round.Tundra, permafrost, or ice cap.Very little precipitation.

Where located

Poleward of boreal forestTHESE 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)

CENTRAL CENTRAL ASIA AND ASIA AND

TIBETTIBET

ROCKY ROCKY MOUNTAINSMOUNTAINS

ANDEANANDEANALTIPLANOALTIPLANO

WE’LL SEE WHAT HAS HAPPENED TO MOUNTAIN GLACIERS INTHESE PLACES LATER…

Summary of Lecture 32The 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