1. © 2011 Pearson Education, Inc. Chapter 18 Preparation and Our Dynamic Climate AP Environmental Science Mr. Grant Lesson 48

2. © 2011 Pearson Education, Inc. Objectives: Complete Chapter 17 Multiple Choice Questions/Take Quiz Chapter 18 Pre-Reading: In class exercise to help activate background knowledge, make connections, stimulate predictions, and form a purpose for reading. Define the terms greenhouse effect and Milankovitch cycle. Describe Earth’s climate system and explain the many factors influencing global climate. Characterize human influences on the atmosphere and climate. Supplementary: What makes Earth habitable? What exactly explains climate change? LiveScience.com explores the science of global warming and shows how conditions here on Earth came to be "just right."

3. © 2011 Pearson Education, Inc. Greenhouse Effect: The warming of Earth’s surface and atmosphere (especially the troposphere) caused by the energy emitted by greenhouse gasses. Milankovitch Cycle: One of three types of variations in Earth’s rotation and orbit around the sun that results in slight changes in the relative amount of solar radiation reaching Earth’s surface at different latitudes. As the cycles proceed, they change the way solar radiation is distributed over Earth’s surface and contribute to changes in atmospheric heating and circulation that have triggered the ice ages and other climate changes. Define the terms greenhouse effect and Milankovitch cycle.

4. © 2011 Pearson Education, Inc.

5. Orbital Parameters: Precession Perihelion Apehelion

6. © 2011 Pearson Education, Inc. Orbital Parameters: Obliquity 22.5° 24.5°

7. © 2011 Pearson Education, Inc. Orbital Parameters: Eccentricity Perihelion Apehelion Minimum: 0.005 Maximum: 0.061 Not to scale! To Scale!

8. © 2011 Pearson Education, Inc. Orbital Parameters & Earth’s Climate Age (kya) 10009008007006005004003002001000 Eccentricity (100 ky) Temperature Obliquity (41 ky) Precession (22 ky) Orbital Parameters

9. © 2011 Pearson Education, Inc. Describe Earth’s climate system and explain the many factors influencing global climate. Earth’s climate changes naturally over time, but it is now changing rapidly because of human influence. The sun provides most of Earth’s energy. Earth absorbs about 70% of incoming solar radiation and reflects about 30% back into space. Greenhouse gases such as carbon dioxide, methane, water vapor, nitrous oxide, ozone and halocarbons warm the atmosphere by absorbing infrared radiation and re-emitting infrared radiation. Earth is experiencing radiative forcing of 1.6 watts/m 2 of thermal energy above what it was experiencing 250 years ago. Milankovitch cycles influence climate in the long term. Solar radiation, ocean absorption, and ocean circulation also influence climate.

10. © 2011 Pearson Education, Inc. What is climate change? Climate change is the fastest-developing area of environmental science Climate = an area’s long-term atmospheric conditions -Temperature, moisture, wind, precipitation, etc. -Weather = short-term conditions at localized sites Global climate change = describes trends and variations in Earth’s climate -Temperature, precipitation, storm frequency Global warming and climate change are not the same

11. © 2011 Pearson Education, Inc. Global warming Global warming = an increase in Earth’s average temperature -Only one aspect of climate change Climate change and global warming refer to current trends -Earth’s climate has varied naturally through time The current rapid climatic changes are due to humans -Fossil fuel combustion and deforestation Understanding climate change requires understanding how our planet’s climate works

12. © 2011 Pearson Education, Inc. The sun and atmosphere keep Earth warm Four factors exert the most influence on climate The sun = without it, Earth would be dark and frozen -Supplies most of Earth’s energy The atmosphere = without it, Earth’s temperature would be much colder The oceans = shape climate by storing and transporting heat and moisture How Earth spins, tilts, and moves through space influence how climate varies over long periods of time

13. © 2011 Pearson Education, Inc. The fate of solar radiation The atmosphere, land, ice, and water absorb 70% of incoming solar radiation

14. © 2011 Pearson Education, Inc. Greenhouse gases warm the lower atmosphere As Earth’s surface absorbs solar radiation, the surface increases in temperature and emits infrared radiation Greenhouse gases = atmospheric gases that absorb infrared radiation -Water vapor, ozone, carbon dioxide, nitrous oxide, methane, halocarbons [chlorofluorocarbons (CFCs)] After absorbing radiation, greenhouse gases re-emit infrared energy, losing some energy to space Greenhouse effect = energy that travels downward, warming the atmosphere and the planet’s surface

15. © 2011 Pearson Education, Inc. The greenhouse effect is natural Greenhouse gases have always been in the atmosphere We are not worried about the natural greenhouse effect -Anthropogenic intensification is of concern Global warming potential = the relative ability of one molecule of a greenhouse gas to contribute to warming -Expressed in relation to carbon dioxide (potential = 1) -Methane is 25 times as potent as carbon dioxide

16. © 2011 Pearson Education, Inc. Carbon dioxide is of primary concern It is not the most potent greenhouse gas, but it is extremely abundant -The major contributor to the greenhouse effects CO 2 exerts six times more impact than methane, nitrous oxide, and halocarbons combined Deposition, partial decay, and compression of organic matter (mostly plants) in wetlands or marine areas led to formation of coal, oil, and natural gas -These deposits remained buried for millions of years

17. © 2011 Pearson Education, Inc. Radiative forcing expresses change in energy Radiative forcing = the amount of change in thermal energy that a given factor causes -Positive forcing warms the surface -Negative forcing cools it Earth is experiencing radiative forcing of 1.6 watts/m 2 more than it is emitting to space – enough to alter the climate

18. © 2011 Pearson Education, Inc. Milankovitch cycles influence climate Milankovitch cycles = periodic changes in Earth’s rotation and orbit around the sun -Alter the way solar radiation is distributed over Earth These cycles modify patterns of atmospheric heating -Triggering climate variation -For example, periods of cold glaciation and warm interglacial times

19. © 2011 Pearson Education, Inc. Solar output and ocean absorption influence climate Solar output = the sun varies in the radiation it emits -Variation in solar energy (e.g., solar flares) has not been great enough to change Earth’s temperature -Radiative forcing is 0.12 watts/m 2 – much less than human causes Ocean absorption = the ocean holds 50 times more carbon than the atmosphere -Slowing global warming but not preventing it Warmer oceans absorb less CO 2 -A positive feedback effect that accelerates warming

20. © 2011 Pearson Education, Inc. Ocean circulation influences climate Ocean circulation = ocean water exchanges heat with the atmosphere, -Currents move energy from place to place The ocean’s thermohaline circulation system affects regional climates -Moving warm tropical water north, etc. -Greenland’s melting ice sheet will affect this flow El Niño–Southern Oscillation (ENSO) -Shifts atmospheric pressure, sea surface temperature, ocean circulation in the tropical Pacific

21. © 2011 Pearson Education, Inc. Characterize human influences on the atmosphere and climate. Increased greenhouse gas emissions enhance the greenhouse effect. By burning fossil fuels, clearing forests, and manufacturing halocarbons, humans are increasing atmospheric concentrations of many greenhouse gases. Human input of aerosols into the atmosphere exerts a variable but slight cooling effect.

22. © 2011 Pearson Education, Inc. Burning fossil fuels transfer CO 2 from lithospheric reservoirs into the atmosphere -The main reason atmospheric carbon dioxide concentrations have increased so dramatically Deforestation contributes to rising atmospheric CO 2 -Forests serve as reservoirs for carbon -Removing trees reduces the carbon dioxide absorbed from the atmosphere Human activities increased atmospheric CO 2 from 280 parts per million (ppm) to 389 ppm -The highest levels in more than 800,000 years What caused levels of CO 2 to increase?

23. © 2011 Pearson Education, Inc. Fluxes of carbon dioxide

24. © 2011 Pearson Education, Inc. Other greenhouse gases add to warming Methane = fossil fuels, livestock, landfills, crops (rice) -Levels have doubled since 1750 Nitrous oxide = feedlots, chemical manufacturing plants, auto emissions, and synthetic nitrogen fertilizers Ozone levels have risen 36% due to photochemical smog Halocarbon gases (CFCs) are declining due to the Montreal Protocol Water vapor = the most abundant greenhouse gas -Contributes most to the natural greenhouse effect -Concentrations have not changed

25. © 2011 Pearson Education, Inc. U.S. emissions of major greenhouse gases

26. © 2011 Pearson Education, Inc. Feedback complicates our predictions Tropospheric warming will transfer more water to the air -But the effects are uncertain A positive feedback loop = more water vapor … more warming … more evaporation … more water vapor … A negative feedback loop = more water vapor … more clouds … shade and cool Earth OR increase evaporation Minor modifications of the atmosphere can lead to major effects on climate

27. © 2011 Pearson Education, Inc. Most aerosols exert a cooling effect Aerosols = microscopic droplets and particles -They have either a warming or a cooling effect Soot (black carbon aerosols) causes warming by absorbing solar energy -But most tropospheric aerosols cool the atmosphere by reflecting the sun’s rays Sulfate aerosols produced by fossil fuel combustion may slow global warming, at least in the short term -Volcanic eruptions reduce sunlight reaching Earth’s surface and cool the Earth

28. © 2011 Pearson Education, Inc. Supplementary: Goldilocks and the Greenhouse: Science and Climate Change Goldilocks and the Greenhouse: Science and Climate Change (5:54)