Chapter 10Global Climate Systems

Geosystems 6eAn Introduction to Physical Geography

Robert W. ChristophersonCharles E. Thomsen

ClimateClimate is weather averaged over time over broader geographic areas.

Usually averaged over 30-yr periods.

Climatology is the study of climate over both time and space.

One central goal is to determine climatic regions, areas with similar weather statistics.

Another central goal is to analyze climate variability over time (like global warming!).

Earth’s Climate System and Classification  Climate Components:

InsolationTemperaturePressureAir MassesPrecipitation  

These help the classification of climatic regions.By using 2 principal climatic components, temperature and precipitation, general climate types are revealed

Climatic Relationships

Figure 10.3

Climate ClassificationProvides an organized and manageable source of information that simplifies rather complex patterns in the real world

Also gives us a common short hand way to describe climates quickly and easily

There are 2 approaches to climate classification: genetic and statistical

Climate ClassificationGenetic classification: based on what major

air masses and global circulations that dominate the climateidealized continent approach

Empirical classification: based on comparisons of climate variables, such as precipitation changes from season to season statistics!

Empirical ClassificationKoppen climate classification

Developed 1918

Developed to correlate the spatial distribution of plants to the spatial distribution of climate

The Koppen-Geiger climate classification system is the updated version in your text

Koppen-GeigerStatistical climate classification based on average monthly temperatures, average monthly precipitation, and total annual precipitation

Takes seasonality into account

Drawbacks: omits winds, temperature extremes, precipitation intensity, amount of insolation, and cloud cover

Köppen’s Climate Classifications

Tropical Climates (A)Average temp of every month > 18ºC

Mesothermal Climates (C)Coldest month average temperature < 18ºC but >-3ºC

At least 1 month average temperature > 10ºC

Microthermal Climates (D)Average temperature of warmest month >10ºC

Average temperature of coldest month < -3ºC

Primary Letters

Köppen’s Climate Classifications

Polar Climates (E)Average temperature of all months  < 10ºC

Dry Arid and Semiarid Climates (B)

Evaporation > precipitation

Highland (H)

Primary Letters

Köppen’s Climate ClassificationsSecondary Letters

These letters are based primarily on seasonal precipitation:

f = adequate rainfall all through the year, no distinct dry season

w = winter dry (keep in mind the hemisphere), if 70% or more of annual rainfall occurs in summer

s = summer dry, if 70% or more of annual rainfall occurs in winter

m = extremely wet summer = monsoon. A climate only.

Köppen’s Climate ClassificationsSecondary Letters

For B climate only:S = semiarid = steppe

W = arid = desert

which results in either BS or BW.

For E climate only:T = tundra

F = perpetual frost = permanent ice

which results in either ET or EF.

Köppen’s Climate ClassificationsTertiary Letters

The third letters in the system are based exclusively on seasonal and annual temperature:

a = hot summer, warmest month > 22°C; C and D only

b = warm summer, warmest month < 22°C; C and D only

c = cool summer, < 4 months over 10°C; C and D only

d = very cold winter, coldest month < -38°C; D only

h = dry-hot, annual temperature > 18°C; B only

k = dry-cold, annual temperature < 18°C; B only

Köppen’s Climate ClassificationsExamples of Combinations

Af = Tropical Rainforest climate type

Am = Tropical Monsoon climate type

BWh = Low-Latitude Hot Desert climate type

Cfa = Humid Subtropical climate type

Csa = Mediterranean climate type

Dfb = Humid Continental climate type

ET = Tundra climate type

Generalized Climate Regions

Figure 10.4

World Climate Classification

Figure 10.5

Climographs

Temperature(curve)

Precipitation(bars)

Climatic Relationships

Figure 10.3

Tropical Climates (A)Tropical Rain Forest Climates (Af)  Tropical Monsoon Climates (Am)  Tropical Savanna Climates (Aw)Consistent daylength and insolation input

= consistent warm temperatures

Dominance by ITCZShifts seasonally with high sun period

Warm ocean currents, unstable maritime air masses

Tropical Rain Forest and Monsoon

Tropical Rain Forest (Af)

Figure 10.7

Tropical Monsoon (Am)

Figure 10.8

Figure 6.21

Tropical Monsoon Climate (Am)

Tropical Savanna (Aw)

Aw Tropical Savanna

Af Tropical Rain Forest

Am Tropical Monsoon

Figure 10.3

Arid and Semiarid Climates (B)

Arid and Semiarid Climates (B)Köppen system:

W = Desert (arid), S = Steppe (semiarid)h = hot (mean annual temp > 18°C)usually found in lower latitudesk = cold/cool (mean annual temp < 18°C)usually found in the midlatitudes

Low-Latitude Hot Desert Climates (BWh)  Midlatitude Cold Desert Climates (BWk)  Low-Latitude Hot Steppe Climates (BSh)  Midlatitude Cold Steppe Climates (BSk)  

Arid and Semiarid Climates (B)

Potential for evaporation exceeds rainfall (called “moisture efficiency”)Cover 35% of Earth’s surfaceMost extensive geographically of the major climate groupsOne-third of U.S. is classified as arid/semiaridPlants are sparse but specifically adapted:

Xerophytes: adapted to aridity, drought resistant, able to store moisture

Arid and Semiarid Climates (B)

Climatic controls:STHP: dry subsiding air over land masses

Shifting STHP: produces semiarid conditions around periphery of arid areas

Rain shadows: leeward sides of mountain ranges that intercept rainfall on windward side

Continentality: interiors of continents far from moderating effects of water bodies

Arid and Semiarid Climates (B)

Low-Latitude Hot Desert Climate (BWh)

Midlatitude Cold Desert Climate (BWk)

Low-latitude hot steppe (BSh)

Midlatitude cold steppe

(BSk)

BWh Low-latitude hot desert

BSk Midlatitude cold steppe