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

Class #11 Wednesday, July 21 1

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

Chapter 16


The earth's changing climate

Chapter 16


Reconstructing Past Climates Techniques

Glacial landscapesCLIMAPIce coresOtolithsDendrochronology

Climate Throughout the AgesEarth 8-15ºC warmer than it is todayIce Age/InterglacialsYounger-Dryas, mid-Holocene maximum

Class #11 Wednesday, July 21 4Fig. 16-CO, p. 438

Class #11 Wednesday, July 21 5Fig. 16-1, p. 440






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.


Class #11 Wednesday, July 21 12Fig. 1, p. 444

Class #11 Wednesday, July 21 13Stepped Art

Fig. 1, p. 444



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



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 (-)




• 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








• 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







• 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.



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


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





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.



Global Warming

• Consequences of Global Warming– Land areas warm faster– Rise in sea level– Fertilize plants

• Land Use Change– Desertification– Plagues and climate

Class #11 Wednesday, July 21 40Table 16-1, p. 460


Class #11 Wednesday, July 21 42Fig. 16-21a, p. 461

Class #11 Wednesday, July 21 43Fig. 16-21c, p. 461






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