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 Class #11 Wednesday, July 21 3

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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 Class #11 Wednesday, July 21 15

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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 (-) Class #11 Wednesday, July 21 17

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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 Class #11 Wednesday, July 21 19

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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 Class #11 Wednesday, July 21 25

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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 20 th 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 Class #11 Wednesday, July 21 32

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 Class #11 Wednesday, July 21 33

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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 Class #11 Wednesday, July 21 39

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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 Class #11 Wednesday, July 21 48

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Fig. 3, p. 465