Transcript Class #11: Wednesday July 21 Earth’s changing climate

Class #11: Wednesday July 21
Earth’s changing climate
Chapter 16
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Chapter 16
The earth's changing climate
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Reconstructing Past Climates
 Techniques
 Glacial landscapes
 CLIMAP
 Ice cores
 Otoliths
 Dendrochronology
 Climate Throughout the Ages
 Earth 8-15ºC warmer than it is today
 Ice Age/Interglacials
 Younger-Dryas, mid-Holocene maximum
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Fig. 16-CO, p. 438
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Fig. 16-1, p. 440
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Reconstructing Past Climate
• Climate During the past 100 years
– Little Ice Age
– Modern warming
• Topic: Ocean Conveyor and Climate Change
– Cold, salty water sinks near Greenland driving
warm water north .
– If the conveyor stops much colder over Europe.
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Fig. 1, p. 444
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Stepped Art
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Fig. 1, p. 444
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Fig. 16-6, p. 445
Reconstructing Past Climate
• Temperature Trend During the Past 100+ Years
– Largest increase in temperature of any century
during the past 1000 years
– 0.6ºC is significant when compared to the last
1000 years
– Scientists point to carbon dioxide and greenhouse
gases as the cause
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Possible Causes of Climate Change
• External Causes
– Change in incoming radiation
– Change in composition of the atmosphere
– Change in Earth’s surface
• Feedback Mechanisms
– Water vapor-greenhouse gas feedback (+)
– Snow-albedo feedback (+)
– Infrared radiation (-)
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Possible Causes of Climate Change
• Plate Tectonics and Mountain Building
– Theory of plate tectonics
– Ridge and subduction
– Mountain interaction with airflow and ocean
currents
• Variation on the Earth’s Orbit
– Milankovitch Theory
• Eccentricity
• Precession
• Obliquity
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Possible Causes of Climate Change
• Atmospheric Particles
– Aerosols = natural + anthropogenic
– Aerosols in the troposphere (sulfate) may cause
cooling die to reflection of radiation
– Topic :Nuclear winter
• Explosions cause debris to rise and circulate absorbing
sunlight creating darkness and cold.
– Volcanic Explosions: ash and dust in the
stratosphere reflect light and cool
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Fig. 16-14, p. 451
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Fig. 16-15, p. 453
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Possible Causes of Climate Change
• Variations in Solar Output
– Sunspots cause more radiation to be generated by
the sun
– Maunder minimum
• Topic: Climate Models
– General circulation models (GCMs) are not perfect
but extremely sophisticated and serves as the
most reliable current predictive tool.
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Global Warming
• Recent Global Warming: Perspective
– Since the beginning of the 20th century average
global surface temperature has increase 0.8ºC
• Radiative Forcing Agents
– Carbon dioxide and other greenhouse gases
disrupt radiative equilibrium, forming an increase
in temperature
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Global Warming
 Advanced Topics:
 Radiative Forcing
 Any change in average net radiation that occurs at the
top of the atmosphere which is due to some change in
the climate system is called radiative forcing.
 Climate Models and Recent Temperature
 It is difficult to unequivocally prove greenhouse
forcing due to the noise in the system.
 Model well sulfate aerosols, greenhouse gases, change
in solar radiation
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Fig. 16-19, p. 457
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Fig. 2, p. 458
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Global Warming
• Future Global Warming: Projections
– Double carbon dioxide levels will cause a surface
warming of 2-4.5ºC
– Uncertainties:
• The effect of water and land on rising levels of carbon
dioxide
• Amount or greenhouse gases
– Question of Clouds
• Clouds reflect radiation and emit infrared radiation,
positive and negative feedbacks.
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Global Warming
• Consequences of Global Warming
– Land areas warm faster
– Rise in sea level
– Fertilize plants
• Land Use Change
– Desertification
– Plagues and climate
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Table 16-1, p. 460
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Fig. 16-21, p. 461
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Fig. 16-21a, p. 461
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Fig. 16-21c, p. 461
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Global Warming
• Topic: The Sahel
– Recent studies suggest that the dry periods were
due to a cooler North Atlantic Ocean and aerosols
from North America may exacerbate
desertification
• Efforts to Curb
– Kyoto Protocol
– Target emissions, credits, sinks
– US has yet to sign protocol
– California implementing protocol
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Fig. 3, p. 465