1. Climate

2. Overview
Climate Components and Controls
Climate Classification and Global
Patterns
Climate Regions
Tropical
Mesothermal
Microthermal
Polar Climates
Dry and Semi-Arid
Highland
Climate Change

3. Climate and Climate Components
Climatology: Studying long term weather patterns in
order to identify areas of similar characteristics
More recently, it has become focused on climate change
Climate Regions: areas of the Earth that exhibit
similar climatic characteristics
Characteristic biomes: forests, savanna, grasslands,
desert, and tundra
Components of Climate
Insolation: Varies with latitude, daylength
Temperature: Varies with latitude, altitude, continental-
maritime effects, pressure systems, air masses
Air masses: Varies with maritime/continental surfaces,
latitude
Moisture: varies with temperature, pressure systems,
continental/maritime surfaces

4. Classification
Classification systems
Empirical classification
uses statistical data to classify
Genetic classification
uses causal factors to classify
Boundaries between climate regions
Are transition zones, not abrupt changes
Shift over time
With climate change, climate regions are
expected to shift poleward between 150-550
km

5. Example: Tropical Monsoon
climates
Empirical classification Genetic classification
high temperatures with The ITCZ influences the
little annual variation onshore flow of warm,
moist air, producing
Over 6 cm of rainfall heavy rainfall during
for 9 – 11 months of the summer months
the year Subtropical Highs
Less than 6 cm of forming over
rainfall for 1 -3 months continental masses
of the year create a dry offshore
flow during the winter
months

6. Köppen-Geiger Climate Classification System (Empirical)
Uses Average monthly temperatures, average monthly rainfall, and total annual
rainfall for classification to distinguish arid areas

7. An Empirical Classification System

9. Some Genetic Generalizations
Monthly average temperatures decrease
with increasing latitude
annual range increases with increasing
latitude
Where a single pressure system
dominates, rainfall patterns are
convectional (highest monthly rainfall
averages correspond to highest monthly
average temperatures – i.e. summer)
ITCZ
Polar High Pressure

10. Where the subtropical highs are present,
effects on weather are variable, depending
on whether they are motivating maritime
or continental air masses
Continental air masses create arid conditions
Maritime air masses create moist condition
In mid latitudes where cyclonic systems are
present, rainfall patterns follow the shift of
the storm tracks
Continental and Maritime influences
Greatest between Northern (more continental)
and Southern Hemispheres (more maritime)
Greater between Asia (continental winter
influences) than North America (maritime and
continental influences during the winter)

14. Tropical Climates
General Characteristics (A)
Lie between Tropics of Capricorn and Cancer
Largest climate region on Earth
Genetic factors
High Insolation: even day length and near vertical sun rays year-
round
ITCZ exerts a great influence for part or all of the year, bringing high
rainfall
Unstable maritime air masses
Empirical factors
Average temperature of each month above 18oC
Little range in annual temperatures
High total annual rainfall, although monthly averages can vary
Subcategories
Tropical Rainforest (Af)
Tropical Monsoon (Am)
Tropical Savanna (Aw)

16. Tropical Rainforest (Af)
ITCZ is present throughout the entire year
High monthly average rainfall throughout
the year – Monthly average > 6 cm
Average monthly temperatures are fairly
high, with a small annual range
Ecosystem
Broadleaf rainforest
Nutrient poor soils
nutrients stored in the vegetation itself
basis of swidden (“slash and burn”) agriculture

18. Tropical Monsoon (Am)
Feature a distinct wet season and dry season
Significant rainfall for 9-12 months of the year ( > 6cm)
ITCZ brings rain from the moist onshore flow of winds
wet summers
Continental subtropical highs create dry seasons through the
dry offshore flow of winds
dry winters
Monthly average rainfall < 6 cm for 1 -3 months per year
Very high amount of rainfall during wet season
Fairly high average monthly temperatures with a small
annual range
Ecosystem
Broadleaf rainforest grading to thorn scrub on margins with
tropical savanna
Soils are nutrient poor, similar to those of the Tropical
Rainforest climate

20. Tropical Savanna (Aw)
Lie poleward of Tropical Rainforest and
Monsoon climates
Features a distinct wet and dry season
ITCZ affects these areas for less than six
months of the year
wet summers
Average Monthly precipitation > 6 cm for 6 – 9
months
Subtropical highs create dry conditions during
the rest of the year
dry winters
Average monthly rainfall < 6 cm for 3 – 6 months
moisture budget deficit during this time
Ecosystem: Savanna (grasslands)

22. Mesothermal Climates
General Characteristics (C)
Mild Mid-latitude climates
Low mid-latitudes
Variable weather patterns
continental and maritime air masses brought into conflict from
shifting pressure systems (e.g., midlatitude wave cyclones during
the winter)
Ocean currents exert strong influence on air masses
East coast currents are warm and strengthen airmasses
West coast currents are cold and weaken air masses
Summers cool with higher latitude (warm – cool)
Summers are humid except under subtropical highs
Monthly average temperatures are above freezing
Monthly average temperature for coldest month between 18 oC and -
3 oC
Monthly average temperature for warmest month above 10 oC
Annual temperature range from 5 – 20 oC

23. Subcategories
Humid Subtropical Climates
Cfa
Cwa
Cwb
Marine West Coast Climates
Cfb
Cfc
Mediterranean Climates
Csa
Csb

25. Humid Subtropical
Occur on the East coast of continents, just
poleward of the tropics
Humid subtropical – hot summer pattern (Cfa)
Winter weather patterns dominated by midlatitude
cyclonic storm tracks which bring precipitation
winter storm tracks follow routes at lower latitudes
Summer patterns dominated by subtropical highs which
bring mT air masses over the continents
Heating by warm ocean currents create instability and
precipitation
Rainfall occurs year-round
Humid subtropical - winter dry pattern (Cwa, Cwb)
Mainly in Asia – “temperate monsoons”: wet-dry
seasons
ITCZ brings rainfall during the summer
Less rainfall during the winter (subtropical highs)
Wettest summer month has 10 times the precipitation of
driest winter month

29. Marine West Coast (Cfb, Cfc)
Occur on West coast of continents
Mild winters, cool summers
mP air masses dominate
Cyclonic storm systems occur throughout the year
rainfall occurs year-round
In Western Hemisphere, mountains along the
West Coast restrict the extent of this climate
region (rain shadow effect)
Exception: Appalachians
Elevation moderates summer temperatures
Cyclonic storms bring rainfall during the winter and
rainfall is enhanced in the summer due to convectional
heating and cooling and orographic effects as well.

33. Mediterranean (Csa, Csb)
Characterized by a distinct wet-dry
seasonal pattern
winter-wet, summer-dry
Wettest winter month has at least 3 times the
precipitation as the warmest summer month
Dominated by Subtropical Highs
Continental (dry) air masses in the summer
Cyclonic storm tracks in the winter (wet)
Moisture deficits in the summer
vegetation adapted to these conditions
hard, waxy leaves retain moisture
chaparral, maquis, mattoral, mallee scrub

35. Microthermal Climates
General characteristics (D)
High mid-latitude climates with severe winters
Increasing seasonality: greater variability in day length
and temperature range
Polar high pressure and subtropical lows are the main
motivators of air masses (cP, mP)
Rainfall follows convectional patterns
At lowest latitudes of this region, cyclonic storm tracks
influence rainfall patterns
Continental effects create dry winter conditions in Asia
Average monthly temperatures decrease with
increasing latitude
1 – 7 months with average below freezing
Warmest month above 10 oC, coldest month below -3 oC
Annual range of temperatures increases dramatically
with increasing latitude
20 – 65 oC differences possible

36. Subcategories
Humid continental hot-summer climates
Dfa
Dwa
Humid continental mild-summer climates
Dfb
Dwb
Subarctic climates
Dfc
Dfd
Dwc
Dwd

38. Humid Continental Hot-Summer (Dfa)
Few months with monthly average
temperatures below freezing
North America
Cyclonic storm tracks from interaction of mT
and cP air masses provide precipitation year-
round, sustained in the summer by
convectional rainfall as well
Asia (Dwa)
Winters dominated by strong dry cP air mass,
producing monsoonal rain patterns
Vegetation
Forests (where precipitation is high)
Grasslands (where precipitation is low)

40. Humid Continental Mild-Summer
Climates Dfb)
Roughly half the year experiences average
monthly temperatures below freezing
Weather patterns dominated by cP air
mass
Rainfall follows a convectional pattern
Summers wetter than winters
Dry winters more pronounced in Asia (Dwb)
Spring melt of winter snows provides additional
moisture input
Thin soils with moderate fertility

42. Subarctic Climates (Dfc, Dfd, Dwc,
Dwd)
Over half the year experiences average
monthly temperatures below freezing
Summers are cool and winters harsh
Extremely high range of temperatures
Weather patterns are dominated by cP air
mass
Rainfall follows a convectional pattern (highest
in the summer)
Low total annual precipitation
Ecosystem features
Boreal forests (taiga forest)
permafrost (soils frozen beneath the surface
year round)

45. Polar Climates
General characteristics (E)
Above 66.5o N/S Latitude
Low levels of insolation
Low sun angle all year
High albedo of snow and ice
Extreme variation in day length
Dominated by Polar High Pressure systems
Low humidity, little precipitation
No true summer
Subcategories
Tundra (ET)
Ice Caps/Sheets (EF)
Polar Marine

47. Tundra Climate (ET)
Average monthly temperatures below
freezing with continuous snow cover for 8
– 10 months each year
Maximum summer temperature no more
than 10oC
Short burst of vegetation when snow melts
lichen, moss, sedges, some flowering plants, no
trees
Permafrost

48. Ice Cap/Ice Sheet Climate (EF)
All monthly average temperatures below
freezing
-78oC has been recorded in Antarctica
Polar high pressure system
Cold, dry air, little precipitation
Ice has accumulated for hundreds of
thousands of years
900,000 years maximum age recorded in an ice
core
dissolved gases in the ice give a profile of changes to
Earth’s atmospheric composition.
Ice sheets can be several kilometers thick

49. Polar Marine Climate
Oceans moderate temperatures
-7oC is maximum low
Colder than Tundra Climates on average
Small annual temperature range (no more than
15oC)
More precipitation than other Polar
climates
sleet
Predominant in coastal areas at the
southern extreme of the Polar range

50. Arid and Semiarid Climates
General Characteristics (B)
Climate Region defined by permanent moisture deficits
The potential demand for water exceeds its availability
throughout the entire year
Deserts: Available moisture is less than half of demand
Steppe: Available moisture is greater than half, but less than the
total demand
Genetic factors
Subtropical highs dominate
Continental effect dominates
Asia
Rain shadows
Vegetation
Xerophytes: plants adapted to retain moisture, such as cacti
Phreatophytes: plants with roots that penetrate deep down to
where the water is

51. Subgroups
Low Latitude Hot Desert Climates
BWh
Midlatitude Cold Desert Climates
Bwk
Low Latitude Hot Steppe Climates
BSh
Midlatitude Cold Steppe Climates
BSk

53. Low Latitude Hot Desert Climates
(BWh)
Tropical and Subtropical
High temperatures (Average annual
temperature above 18oC)
0 – 38 cm rainfall annually
Dominated by Subtropical Highs,
Continental Effect
Typically occur on western edges of continents,
but desert conditions extend across North
Africa into Saudi Arabia
When the subtropical highs depart, instead of moist
wind being brought in from the east, dry wind off the
Asian steppes and deserts is brought in instead
Rainfall follows a convectional pattern

54. ITCZ?

55. Midlatitude Cold Desert Climate (BWk)
Occur at higher latitudes and elevations
than hot deserts
Average precipitation is below 25cm
annually
Average annual temperature is below 18 oC
Rainfall comes with convectional patterns
and midlatitude cyclonic storm systems
Locations
Southwest US into Nevada
Asia (Gobi Desert and Mongolia)
Patagonian Desert in Argentina

57. Low-Latitude Hot Steppe Climates (BSh)
Occur on the margins of hot deserts where
precipitation is a little higher
Average annual precipitation is between 38 – 76 cm
Convectional rainfall pattern
Average annual temperature is above 18 oC
Midlatitude Cold Steppe Climate (BSk)
Occur on the poleward margins of cold deserts
25 – 64 cm of precipitation per year
Precipitation is both convectional and cyclonic
in origin
Average annual temperature is below 18 oC

59. Highland Climates
Not one single climate, but a gradual
gradation of climate types as one
moves up a mountain slope
Increases in altitude correspond to
increases in longitude
Vegetation changes correspondingly
Orographic rainfall plays a crucial role in
the climate
Wet/dry climate conditions with rain
shadow effect
Mountain-Valley breezes are important
regulators of temperature

61. C
A D
B
E

62. Global Climate Change
Evidence
Global average temperatures since 1998 have
been the highest on record
Rate of increase of temperatures is highest on
record
Within 1oC of meeting the highest temperatures of
the last 125,000 years (which are the highest on
record over the last 440,000 years)
Concentration of CO2 is the highest over the last
440,000 years
Challenge: what warming effects are
anthropogenic forcing, and which are natural
forcing?

65. Data sources
Contemporary climatology
Direct atmospheric monitoring
Paleoclimatology
Ice cores
Tree-ring density
Sediments
Coral reefs
Pollen

66. Causes
Greenhouse gases
90-99% certainty that global warming is from the build-up
greenhouse gases
Carbon dioxide (CO2)
Accounts for 64% of warming
33% increase over pre-industrial levels
Attributed to the burning of fossil fuels and net loss of forest
Methane (CH4)
Accounts for 19% of warming
over 100% increase over pre-industrial levels
Attributed to anaerobic oxidation of organic compounds
50% from livestock digestion and organic processes in rice fields
Nitrous oxide (N2O)
Up 17% over pre-industrial period
Attributed to fertilizer use – with some uncertainty
Halocarbons (CFCs)
Absorb a different wavelength of infrared radiation than carbon dioxide
reduction in stratospheric ozone creates more surface warming
Directly attributable to human activity

68. Predicted changes
Based on General Circulation Models
Three scenarios (1990-2100)
Low Forecast – 1.4oC
Middle Forecast – 3.6oC
High Forecast – 5.8oC
The Arctic is warming at a rate greater
than that predicted by the high forecast

69. Effects of global warming
Droughts that threaten food supply
crops very sensitive to climatic conditions
Shifting climatic regions
species redistribution
Polar species especially are at risk
Melting of ice sheets/caps and glaciers
11% of Antarctica is composed of ice shelves
8000 km2 have disintegrated since 1993
Changes in sea level
Low forecast – 0.09 m
Medium forecast – 0.48 m
High forecast – 0.88 m
25% in rise attributable to thermal expansion of water

70. Kyoto Protocol
Calls for an overall reduction in carbon
dioxide levels of 5.2% (1990 levels)
between 2008-2012
Some countries favor a 15% reduction by 2010
Individual country contributions
European Union – 8%
Australia – 8%
Canada – 6%
USA – 7%, but never ratified the treaty and
withdrew from the process in 2001