31 The Changing Face of the Earth Before After Flooding of Mississippi & Illinois Rivers 1993 According to plate tectonic theory, which of these should have the most violent earthquakes, on average? 1. The midocean ridges 2. Subduction zones near continental margins 3. Suture zones at collisions of two continental plates 4. Hot spots PS 100 -- Chapter 31 1 PS 100 -- Chapter 31 2 What is a Natural System? Hydrologic System Group of natural, interdependent parts or components Interactions between parts forms the system Forces drive the system All systems tend toward a state of maximum disorder (entropy) called equilibrium Earth s two major systems are: Tectonic System Hydrologic System System of moving water Rivers Oceans, Lakes Glaciers Groundwater Water Vapor in Atmosphere Effects of Hydrologic System Erosion Transportation of Sediment Deposition of Sediment Creation of Numerous Landforms PS 100 -- Chapter 31 3 PS 100 -- Chapter 31 4 Hydrologic System Where is most of the water in Earth s hydrologic system? 1. In the atmosphere 2. Locked up as glacial ice 3. In freshwater streams and lakes 4. In the oceans PS 100 -- Chapter 31 5 PS 100 -- Chapter 31 6 1
What Forces Drive this System? Solar Radiation Average ~342 W/m 2 = ~342 joules/sec m 2 Causes evaporation Gravity Pulls water down slopes Causing erosion, transportation of sediment Subsystems of Hydrologic System River Systems Glacial Systems Groundwater Systems Ocean/Shoreline Systems Desert Systems PS 100 -- Chapter 31 7 PS 100 -- Chapter 31 8 Rivers Primary mechanism for erosion Move sediment from mountains to oceans Also carry dissolved ions (salts) Can be easily disturbed by human activity Dams Pollution Irrigation PS 100 -- Chapter 31 9 PS 100 -- Chapter 31 10 Glaciers Rivers (or oceans) of ice Very effective agents of erosion Carve different topography than rivers Many glaciers are currently shrinking PS 100 -- Chapter 31 11 PS 100 -- Chapter 31 12 2
2004 1875 Pasterze Glacier, Austria PS 100 -- Chapter 31 13 PS 100 -- Chapter 31 14 Continental Glaciers Iceland Groundwater NOT in underground lakes or rivers; in ROCKS Rocks can hold a lot of water! Porosity Permeability Groundwater is a major source of drinking and irrigation water Groundwater is often affected by human activity Overpumping Pollution Irrigation PS 100 -- Chapter 31 15 PS 100 -- Chapter 31 16 Water Table PS 100 -- Chapter 31 17 A spring in the Grand Canyon PS 100 -- Chapter 31 18 3
Sinking San Joaquin Removal of ground water for agriculture Land subsiding PS 100 -- Chapter 31 19 PS 100 -- Chapter 31 20 Oceans & Shorelines Hurricane Katrina, 2005 Beautiful, but changeable Shorelines are places of active Erosion Transportation Deposition Human activity can have a significant effect on shorelines PS 100 -- Chapter 31 21 PS 100 -- Chapter 31 22 9 th Ward Breach in the Industrial Canal a day after Katrina passed over New Orleans. This neighborhood was built over a cypress swamp. Waves from Lake Ponchartrain and Lake Borgne broke the manmade levees. Vincent Laforet New York Times National Geographic PS 100 -- Chapter 31 NASA23 PS 100 -- Chapter 31 24 4
Deserts Dominated by wind (Eolian system) Carries light-weight particles (sand & dust) Leaves the rest behind Human effects Desertification Overgrazing Poor Farming Practices Destruction of Soil Irrigation adds salts PS 100 -- Chapter 31 Smiley Pool, 25 Dallas Morning News PS 100 -- Chapter 31 26 Global Warming Is Earth getting warmer? What have been trends in the past? How do we know? What causes the changes? Should we do anything? PS 100 -- Chapter 31 27 PS 100 -- Chapter 31 28 Year, A.D. What is Earth s Past Climate History? How do we know? Past Temperatures and Atmospheric CO 2 Levels Correlate Cause or effect? PS 100 -- Chapter 31 29 PS 100 -- Chapter 31 30 5
Natural Climate Cycles: Solar Radiation Orbital eccentricity: 100ky Axial inclination: 41ky Axial precession: 23ky According to these cycles, we should be entering a new ice age PS 100 -- Chapter 31 32 PS 100 -- Chapter 31 31 Clouds, Ash, Pollution PS 100 -- Chapter 31 33 PS 100 -- Chapter 31 34 Greenhouse Gases Certain gases trap heat in the atmosphere (transmit visible light to ground, absorb infrared that ground emits) Water vapor (H 2 O) Carbon dioxide (CO 2 ) Methane (CH 4 ) Venus has a runaway greenhouse due to CO 2 Surface temperatures hot enough to melt lead! PS 100 -- Chapter 31 35 PS 100 -- Chapter 31 36 6
What is the evidence that Earth is warming up? Recent Sea Level Changes Not only are we not entering an ice age, but we are also definitely seeing higher average temperatures. PS 100 -- Chapter 31 37 PS 100 -- Chapter 31 38 Can you figure it out? Melting the continental glaciers on Greenland and Antarctica will cause a rise in sea level. Why won t the north polar ice sheet do the same? Geologic record indicates that past sea level changes when polar glaciers melt have been hundreds of meters. The cost would be catastrophic. PS 100 -- Chapter 31 39 PS 100 -- Chapter 31 40 Atmospheric Methane Levels ICE CORE DATA Possible Human Effects on Climate PS 100 -- Chapter 31 41 Declining CO 2 trend reversed 8000 years ago Correlates with clearing of European forests & beginning of rice cultivation Declining CH 4 trend reversed 5000 years ago Correlates with flooding of lowlands and beginning of rice cultivation PS 100 -- Chapter 31 42 7
Should we do anything? Risk, Cost, & Benefit Cost of reducing greenhouse emissions will certainly be billions of dollars Certainty of global warming is not 100% Current predictions depend on imperfect models Environmental and economic consequences could be truly catastrophic Some say global warming could cause the end of technological civilization As voters & consumers, these are your issues PS 100 -- Chapter 31 43 PS 100 -- Chapter 31 44 Which best describes your opinion on global warming? A. This is just political hype. No action is needed. B. We should wait until the models are better before we do anything. C. I d like beachfront property in Utah. Do nothing and party on! D. We should invest the $billions needed to find ways to reduce greenhouse gas emissions. E. We are already in danger. We should immediately stop driving cars! PS 100 -- Chapter 31 45 PS 100 -- Chapter 31 46 8