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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

Climate

What is the difference between weather and climate?Arctic Sea ice changes: 1977 (top) to 2007 (bottom)

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


• Thornthwaite System– Classifying based on

moisture– Used often by soil

and water resource scientists

– Potential evapotranspiration

– Actual evapotranspiration


What can you suggest are the causes for the major climate changes as you follow the 40o latitude line from west to east?


What is the Thornthwaite climate type for coastal California?


• 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.


• 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


Simplified Köppen System


• 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)


• Tropical (A) Climate– Aw (dry winter tropical

savanna)– Am (along coast with

tropical monsoon)


World Map of modified Köppen Classification System


• 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


• 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.


• 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


• 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)


• 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)


• Highland (H) Climates– Mountain barriers can

increase and decrease precipitation, cloud cover, and temperature.

– Windward – wetter– Temperature decreases

as you increase in elevation.


• Climate Regions– Region: similar internal

characteristics distinct from other areas.

– Transition

• Scale of Climate– Microclimate– Topoclimates– Lake effect snow– Urban heat-island effect

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?


• Modern Research– Radiometric techniques– Ocean sediment

• Calcium carbonate and shells

• Oxygen-isotope record– Holocene


Q: Has the general trend of temperature on Earth been warmer or colder during the Holocene?


• Methods for Revealing Climates of the Past– Paleoclimates– Oxygen-Isotope Ratio of

Calcium carbonate and shells

– Ice cores– Dendrochronology– Palynology


• 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

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

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


• Changes in Earth’s Atmosphere– Volcanic Activity

• Tambora (1815, 1816)

• Krakatoa (1883)• Mount Pinatubo

(1991)– Greenhouse Gases


• 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)


• Which greenhouse gas has the longest residence time?


• 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


• Impact Events– Asteroids– Comets– Tunguska Event– 65 mya– Near Earth Objects

(NEO)

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.

8.5 Predicting Future Climates

• Global warming– most scientists believe

that global warming is occurring.

– Most mountain glaciers are retreating

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.


• On what continent has the observed temperature fluctuated the most during this time period, and which one the least?


• 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

Physical Geography

End of Chapter 8: Global Climates and Climate Change

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Education

classifying climates

global climates

major climate changes

humid tropical c

climate high temp year

major climate zones

thornthwaite climate

o c et tundra