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Chapter 8: Global Climates and Climate Change
Physical Physical GeographyGeographyNinth EditionNinth Edition
Robert E. Gabler
James. F. Petersen
L. Michael Trapasso
Dorothy Sack
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Climate
What is the difference between weather and climate?Arctic Sea ice changes: 1977 (top) to 2007 (bottom)
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8.1 Classifying Climates
• Early Greeks (Aristotle): Torrid, Temperate, and frigid
• Two weather variables most often used today:– Temperature (minimum of 30 years of data)– Precipitation (minimum of 30 years of data)
• Classify Climate– Atmospheric elements (statistics and math) =
empirical– Based on the cause = genetic
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8.1 Classifying Climates
• Thornthwaite System– Classifying based on
moisture– Used often by soil
and water resource scientists
– Potential evapotranspiration
– Actual evapotranspiration
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8.1 Classifying Climates
What can you suggest are the causes for the major climate changes as you follow the 40o latitude line from west to east?
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8.1 Classifying Climates
What is the Thornthwaite climate type for coastal California?
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8.1 Classifying Climates
• Köppen System– Most widely used– Based on regional temperature and precipitation– Advantages:
• Easy to measure• Measured most often• Most important
– Disadvantages:• Only average monthly temp and precip.• Ignored winds, clouds, intensity of precip.
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8.1 Classifying Climates
• Simplified Köppen System– Divided into six major climate zones
• A = Humid Tropical• C = humid mesothermal (mild winter)• D = humid microthermal (severe winter)• E = polar• BW and BS = arid and semiarid• H = Highland
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8.1 Classifying Climates
Simplified Köppen System
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8.1 Classifying Climates
• Tropical (A) Climate– High temp year round– Near equator– No winter season
(average temp of coldest month above 18oC (64.4oF)
– ITCZ– Af (tropical rainforest)
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8.1 Classifying Climates
• Tropical (A) Climate– Aw (dry winter tropical
savanna)– Am (along coast with
tropical monsoon)
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8.1 Classifying Climates
World Map of modified Köppen Classification System
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8.1 Classifying Climates
World Map of modified Köppen Classification System
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8.1 Classifying Climates
• Polar (E) Climate– No month has an average temp grater
than 10oC (50oF)
– EF (ice sheet): no month > 0oC
– ET (tundra): at least 1 month averages > 0oC
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8.1 Classifying Climates
• Mesothermal (C) Climate– 1 month below average temp
grater than 18oC (64.4oF) and 1 month below 10oC (50oF)
– Csa and Csb (Mediterranean)• Dry summer• Along west coasts between 30o and
40o latitude
– Cfa (humid subtropical)• Wet year round• Southeast U.S.
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8.1 Classifying Climates
• Mesothermal (C) Climate– Cfb and Cfc (marine west
coast)– Wet year round– Summer’s cooler than Cfa– Along west coasts often
extending up to 40o latitude
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8.1 Classifying Climates
• Microthermal (D) Climates– Usually year round precip.– Shorter summers and colder
winters than “C”– Found only in N. hem.– Dfa and Dwa (humid continental,
hot summer)– Dfb and Dwb (humid continental,
mild summer)– Dfc, Dfd, Dwc, and Dwd
(subarctic)
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8.1 Classifying Climates
• Arid (B) Climates– Year round moisture deficiency– Precip received < potential ET– 15o to 30o latitude – BW (desert, annual precip. is less
than half of annual potential ET)– BS (steppe; annual precip. is less
than potential ET, but more than half)
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8.1 Classifying Climates
• Highland (H) Climates– Mountain barriers can
increase and decrease precipitation, cloud cover, and temperature.
– Windward – wetter– Temperature decreases
as you increase in elevation.
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8.1 Classifying Climates
• Climate Regions– Region: similar internal
characteristics distinct from other areas.
– Transition
• Scale of Climate– Microclimate– Topoclimates– Lake effect snow– Urban heat-island effect
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8.2 Climates of the Past
• Ice Ages– Glaciation (cold period)– Interglacial (warmer
period)– Pleistocene
Q: Why does the ice move in various directions in difference regions of the continent?
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8.2 Climates of the Past
• Modern Research– Radiometric techniques– Ocean sediment
• Calcium carbonate and shells
• Oxygen-isotope record– Holocene
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8.2 Climates of the Past
Q: Has the general trend of temperature on Earth been warmer or colder during the Holocene?
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8.2 Climates of the Past
• Methods for Revealing Climates of the Past– Paleoclimates– Oxygen-Isotope Ratio of
Calcium carbonate and shells
– Ice cores– Dendrochronology– Palynology
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8.2 Climates of the Past
• Methods for Revealing Climates of the Past (con’t)– Palynology:
• pollen-analysis• A core is drilled and
removed to show the layers of the sediment.
• Organic material can be radiocarbon dated.
• Paleoclimatologists reconstruct the climate
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8.3 Rates of Climate Change
• Altithermal– 7000 ya (years ago)– Warmer than today
• What was the evidence?– Ice record from Antarctica
and Greenland (oxygen-isotope.
– Rapid change (few years or a decade)
– Positive feedback system
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8.4 Causes of Climate Change
• Orbital Variations (Milankovitch Cycles)– Eccentricity:
• 100,000 years• Shape of Earth’s orbit
– Obliquity• 41,000 years• Tilt of Earth’s axis 24.5o - 22o
– Precession• 21,000 years• Distance to the sun
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8.4 Causes of Climate Change
• Changes in Earth’s Atmosphere– Volcanic Activity
• Tambora (1815, 1816)
• Krakatoa (1883)• Mount Pinatubo
(1991)– Greenhouse Gases
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8.4 Causes of Climate Change
• Greenhouse Gases– Carbon Dioxide (CO2)
• Blocks outgoing longwave radiation
• CO2 and ice sheets
• Increasing trend (~ 380 ppm as of 2007).
– Methane (CH4)
• Very effective, however, currently very low.
– CFC’s
– Nitrous Oxides (N2O)
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8.4 Causes of Climate Change
• Which greenhouse gas has the longest residence time?
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8.4 Causes of Climate Change
• Changes in the Ocean– ENSO– Thermohaline Circulation
• Changes in Landmasses– Shifting land masses (e.g.
Continent over the poles)– New land blocking oceanic
or atmospheric circulation– Change in albedo
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8.4 Causes of Climate Change
• Impact Events– Asteroids– Comets– Tunguska Event– 65 mya– Near Earth Objects
(NEO)
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8.5 Predicting Future Climates
• Little Ice Age (1560-1850)
• General Circulation Models (GCM’s)
• Milankovitch Cycles
• Greenhouse Gases
• Global warming: most scientists believe that global warming is occurring.
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8.5 Predicting Future Climates
• Global warming– most scientists believe
that global warming is occurring.
– Most mountain glaciers are retreating
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8.6 The Issue of Global Warming
• The climate changes naturally
• However, the vast majority of scientists content that humans are affecting our atmosphere.
• IPCC (Intergovernmental Panel on Climate Change)“very likely that emissions of greenhouse gases
from anthropogenic activities have caused” … most of the observed increase in globally-averaged temperature since the mid-20th century.
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8.6 The Issue of Global Warming
• On what continent has the observed temperature fluctuated the most during this time period, and which one the least?
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8.6 The Issue of Global Warming
• Recommendations for the Future– Global Scale– Simple things we can do that will help reduce
our negative impact on Earth’s fragile environment:• Use car pools and mass transit• Drive smaller cars• Use more energy-efficient lighting and
appliances• Recycle
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Physical Geography
End of Chapter 8: Global Climates and Climate Change