class #11: wednesday july 21 earth’s changing climate chapter 16 1class #11 wednesday, july 21
TRANSCRIPT
Class #11 Wednesday, July 21 3
Reconstructing Past Climates
TechniquesGlacial landscapesCLIMAPIce coresOtolithsDendrochronology
Climate Throughout the AgesEarth 8-15ºC warmer than it is todayIce Age/InterglacialsYounger-Dryas, mid-Holocene maximum
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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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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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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 TemperatureIt 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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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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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