Chapter 13 The earth's changing climate
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
Reconstructing Past Climate • Topic: Ocean Conveyor and Climate Change • Cold, salty water sinks near Greenland driving warm water north. • If the conveyor stops much colder over Europe • Climate During the past 100 years • Little Ice Age • Modern warming
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
Climate Change by Natural Events • 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 (-)
Climate Change by Natural Events • 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 • Milankovich Theory • Eccentricity • Precession • Obliquity
Stepped Art Fig. 13-11, p. 384
Climate Change By Natural Events • Variations in Solar Output • Sunspots cause more radiation to be generated by the sun • Mauncher minimum • Topic: Climate Models • General circulation models (GCMs) are not perfect but extremely sophisticated and serves as the most reliable current predictive tool.
Climate Change by Humans • Atmospheric Particles • Aerosols = natural + anthropogenic • Aerosols in the troposphere (sulfate) may cause cooling due 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
Climate Change by Humans • 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
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.
Climate Change by Humans • 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
Climate Change by Humans • 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
Climate Change by Humans • Consequences of Global Warming • Land areas warm faster • Rise in sea level • Fertilize plants • Land Use Change • Desertification • Plagues and climate