Patterns of Global Climate
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3atterns of Global Climate
Aims
To be able to explain how the global patterns translate into typical local climates
To describe how climate patterns relate to biomes
Objectives
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to describe the global patterns of temperature, precipitation, pressure and winds
to relate these patterns to the forcing of the climate system
to describe the global ocean circulation and its causes
to show how the global patterns play out locally for typical climate regions
to describe how climate patterns relate to biomes
Required reading
Smithson, P., K. Addison, and K. Atkinson, 2002. Fundamentals of the Physical Environment. Routledge, 560pp.Chap.11 p 219,220, Chap. 20 p 423-426.
Briggs, D., Smithson, P., K. Addison, and K. Atkinson, 1997. Fundamentals of the Physical Environment. Routledge Chap. 4 p 57-59, Chap. 20 p 363-369.
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Patterns of Global Climate
Outline
Introduction
• Climate and plant distribution
Climate patterns
• Atmospheric variables
• Ocean circulation
Climate classification
Climate classification schemes
• Koeppen’s system
• Thornthwaite’s system
• The Holdridge system
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Patterns of Global Climate
Bullets
Introduction
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Regularities in climate, climate zones
Climate and plant distribution: plant distribution closely related to climate distribution
Precipitation
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Pressure distribution important
In areas with low pressure and converging and rising air the air with cool during
ascent and rain will form.
In areas with high pressure and diverging and sinking air the air is coming from above
and thus already and will warm during descent - thus dry conditions prevail
Inherent properties of air are also important, its temperature and previous movement
warm air can hold much water, thus higher potential for strong rains in warm areas
much lower potential for precipitation in cold regions since the air has lost most of its
water vapor content during cooling and low temperatures reduce evaporation
Zonal distribution: tropical low pressure band - ITCZ - being the convergence zone of
the trade winds with warm and moist air receives abundant precipitation all year
Subtropical high pressure areas dry due to subsidence of air from above
Midlatitudes receive precipitation due to traveling cyclonic storms and their fronts
Polar regions experience only meager precipitation since the air is cold and any significant evaporation is not possible in polar regions - thus water vapor has to come
from regions over a significant distance. Additionally high pressure blocks air movement into the polar regions.
Seasonally shifts of the ITCZ and the subtropical highs lead to summer rain bands
between the continuously wet part of the tropics and dry parts of the subtropics.
The seasonal shift on the polar jets lead to winter rain areas between the continuously dry parts of the subtropics and the wet parts of the midlatitudes.
Anomaly in the zonal distribution of precipitation in the subtropics due to dry and wet
sides of the subtropical highs. West sides of those highs tend to have wet air due to
the movement of the subsiding air from the east and south side over the tropical
ocean picking up water vapor
The impact of mountain barriers can be seen by comparing North America with
South-North ranges and Europe, Russia and Siberia with predominantly West-East
ranges. The Westerlies can sweep fairly unimpeded over Europe and can bring precipitation much further inland than in North America where the Rockies lead to mountain shadow deserts
Climate classification
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plant species typically limited by physical environment - in part by climate.
development of specialists which grow better in harsh environments than other species - but not as well as generalists in good environments
Thus climate patterns will be important to understand species distribution
simplify complexity of climate system to apply simple rules for relationships with plant
life zones
understand plant distribution
use well observed climate variables for classification
Classify climates based on the vegetation type one would expect under the given climate.
Patterns of Global Climate
Biome A community of animals and plants occupying a climatically uniform area on a
continental scale.
Bioclimatic classification scheme A method for relating climatic variables to the
distribution of vegetation and its characteristics at a global scale. Examples include
the Holdridge scheme, the Thornthwaite scheme, the Koeppen scheme, and the Troll
and Paffen scheme. See Prentice (1990).
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Climate classification schemes
The Koeppen classification
Koeppen conceived the idea, that plants integrate climate and that their distribution
therefore defines climate regions - vegetation type as a crystallization of climate
forms basis of classification: e.g. 10°C isotherm of warmest month corresponds
roughly to northern tree line
based on seasonality and mean characteristics of temperature and precipitation
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Table 1: Koeppen climate zones
Primary Letters
Secondary Letters
Tertiary Letters
A
Tropical wet or wet/
dry
f
w
m
Precipitation yr-round
concentr. in Summer
monsoon
B
Dry (desert and
steppe)
W
S
desert
steppe
k
h
cold or cool,
warm or hot
C
Humid Sub-tropical
f
w
s
Precip. yr-round
conc in Summer
conc in winter
a
b
c
hot summer
warm summer
cool summer
D
Humid Continental
f
w
s
Precip. yr-round
conc in Summer
conc in winter
a
b
c
d
hot summer
warm summer
cool summer
severe winter
E
Polar or Ice-cap
T
F
tundra
ice
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None
Quantitative Distinctions:
main variables for characterization:
mean temperature of: coldest month TMIN, warmest month TMAX
precipitation of:
wettest summer month PSMAX, driest summer month PSMIN,
wettest winter month PWMAX, driest winter month PWMAX,
driest month PMIN
annual mean precipiation PA
threshold value of precipitation PD, depending on annual mean temperature
A: tropical: TMIN > 18°C, annual precipitation above t hreshold value
subtypes:
AF : tropical rainforest (PMIN ≥ 60 mm/month)
Aw : tropical savanna (PMIN < 60 mm/month)
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Patterns of Global Climate
B: arid: TMIN > 18°C and PA " PD
subtypes:
BW : desert climate (PA ≥ PD/2)
BS : steppe climate (PA < PD/2)
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C: temperate (humid mesothermal): TMIN ≥ -3°C and TMIN < 18°C
subtypes:
Cs: dry summer (PWMAX ≥ 3 PSMIN)
Cw : dry winter (PSMAX ≥ 10 PWMIN)
Cf: humid (neither Cs or Cw)
D: cold (humid microthermal): TMIN < -3°C and TMAX ≥ 10° C
subtypes:
Df: wet winter (PSMAX < 10 PWMIN)
Dw: dry winter (PSMAX ≥ 10 PWMIN)
E: polar: TMAX < 10°C
subtypes:
ET: tundra climate: 0°C " TMAX < 10°C
EF: permanent ice cover: TMAX < 0°C
Thornthwaite’s system
Thornthwaite pointed out that the Koeppen scheme does not work well for forest climates
Tries to include a measure of monthly water deficit as forests rely on continually available moisture.
The Holdridge system
Relies on annual precipitation and mean annual biotemperature - can be derived from
often readily available data
Further reading
W. R. Emanuel, H. H. Shugart, and M. P. Stevenson, 1985. Climatic change and the
broad-scale distribution of terrestrial ecosystem complexes. Clim. Change, 7:-43.
L. R. Holdridge, 1947. Determination of world plant formations from simple climatic data.
Science, 105: -368.
Katharine C. Prentice, 1990. Bioclimatic distribution of vegetation for general circulation
model studies. J. Geophys. Res., 95: 811-830.
C. W. Thornthwaite, 1948. An approach toward a rational classification of climate. Geogr. Rev., 38-89.
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Patterns of Global Climate
Introduction
• Consider global climate patterns
• Atmospheric and oceanic circulation
• Relationship between climate and biome distributions
• Consider local climate patterns for typical continental scale climates
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Patterns of Global Climate
Climate
• Global patterns and seasonality
• Temperature
• Winds and pressure
• Precipitation
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Patterns of Global Climate
Temperature
Mean monthly
temperatures
25o
15o
5o
Reflect
January
July
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- solar insulation
- land sea
distribution
- ocean currents
Source: Lutgens, F.K. and E.J.
Tarbuck, 1998. The Atmosphere
Patterns of Global Climate
Winds and Pressure
Mean monthly
winds and pressure systems
January
Reflect
Temperatures
Forces
Atmospheric
circulation
Land-sea
distribution
July
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Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
Patterns of Global Climate
The three cell model and precipitation
Hadley cell
Hadley cell
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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Patterns of Global Climate
Ocean circulation
Mainly wind driven
Equatorial current
Land barriers
•Kuroshio
•Gulf Stream
•Equatorial
counter current
Ocean gyres
Surface circulation
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Heat transport
Patterns of Global Climate
Precipitation
Monthly precipitation
Reflects:
Temperature
Water availability
Pressure
Winds
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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Patterns of Global Climate
Climate classification
Plant species limited by physical environment
use plant distribution to describe climate
Principle:
Plants integrate climate; their distribution therefore defines climate
regions
Biome: A community of animals and plants occupying a climatically uniform area on a continental scale.
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Patterns of Global Climate
Bioclimatic classification scheme
A method for relating climatic variables to the distribution of vegetation
and its characteristics at a global scale
Detailed climate patterns complex, however, not every detail is relevant
Classification
• simplify complexity of climate patterns
• apply simple rules for relationships with plant life zones
Use well observed climate variables for classification
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Patterns of Global Climate
Climate classification schemes
The Koeppen classification
Based on seasonality, mean characteristics of temperature and precipitation
Quantitative description
Thornthwaite’s system
Thornthwaite: Koeppen scheme does not work well for forest climates
Include measure of water deficit; forests rely on continually available moisture
The Holdridge system
Relies on annual precipitation and mean annual biotemperature - can be
derived from often readily available data
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Patterns of Global Climate
Koeppen climate zones
Primary Letters
A Tropical wet or wet/
dry
B Dry (desert and
steppe)
C Humid Sub-tropical
D Humid Continental
E Polar or Ice-cap
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Secondary Letters
f Precip yr-round
w conc. in Summer
m monsoon
W desert
S steppe
f Precip. yr-round
w conc. in Summer
s conc. in winter
f Precip. yr-round
w conc. in Summer
s conc. in winter
T tundra
F ice
Tertiary Letters
None
k
h
a
b
c
a
b
c
d
cold or cool,
warm or hot
hot summer
warm summer
cool summer
hot summer
warm summer
cool summer
severe winter
Patterns of Global Climate
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Patterns of Global Climate
Climate Diagrams
Seasonal cycles of precipitation and temperature
A Climates
Af Tropical wet/dry, year round precip.
Aw Tropical wet/dry, summer precip.
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Patterns of Global Climate
B climates
Bsh
Dry hot
steppe
Bsk
Dry cold
steppe
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C
Bwh
Dry hot
desert
Bwk
Dry cold
desert
Patterns of Global Climate
C climates
Cfa Humid Sub-tropical
hot summer, year round precip.
Cs Humid Sub-tropical
winter precipitation (summer dry)
Cfb Humid Subtropical
warm summer,
year round precip.
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Patterns of Global Climate
D and E climates
Dfa Humid
Continental
year round
precip, hot
summer
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Dwd Humid
Continental
summer
precip., cool
summer
Dfb Humid
Continental
year round
precip, warm
summer
ET Polar or
Ice-cap
tundra
Patterns of Global Climate
Holdridge scheme
Evaluation of climate change
impacts
Holdridge Life Zones
Created at IIASA
Holdridge Life Zones
Doubled CO2 Concentration (IIASA)
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Patterns of Global Climate
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Patterns of Global Climate
Summary
• Global patterns in climate variables
• Coherent variation of variables
• Climate classes
• Biomes reflect climate patterns
• Classification results in typical local climates
• Classification allows prediction of biome patterns
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