© 2011 Pearson Education, Inc. AP Environmental Science Mr. Grant Lesson 45 Chapter 18 Preparation and Our Dynamic Climate

© 2011 Pearson Education, Inc. Mastery Check Why is carbon dioxide considered the main greenhouse gas? Why are carbon dioxide concentrations increasing in the atmosphere? Although carbon dioxide has a lower global warming potential than some other greenhouse gases, its abundance in the atmosphere gives it the most influence over climate of all gases whose concentrations are being increased by human activity. The sudden flux of carbon from lithospheric reservoirs into the atmosphere is the main reason atmospheric carbon dioxide concentrations have increased so dramatically.

© 2011 Pearson Education, Inc. Objectives: Complete Chapter 17 Multiple Choice Questions/Take Quiz 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 on 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."

© 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.

© 2011 Pearson Education, Inc.

Orbital Parameters: Precession Perihelion Apehelion

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

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

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

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

© 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 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, solar radiation, ocean absorption, and ocean circulation all influence climate.

© 2014 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

© 2014 Pearson Education, Inc. What is climate change?  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

© 2014 Pearson Education, Inc. Three factors influence climate  Without the sun, Earth would be dark and frozen  Without the atmosphere, Earth’s temperature would be much colder (as much as 33  C [59  F] colder)  The oceans store and transport heat and moisture  Together, they influence climate  The sun supplies most of the planet’s energy  The atmosphere and water absorb abut 70% of the incoming solar radiation (and reflect 30% into space)  The absorbed energy powers wind, waves, evaporation, and photosynthesis

© 2014 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])

© 2014 Pearson Education, Inc. Greenhouse gases warm the lower atmosphere  After absorbing radiation, greenhouse gases re-emit infrared energy, losing some energy to space  Greenhouse effect  phenomenon in which energy travels downward, warming the atmosphere and the planet’s surface

© 2014 Pearson Education, Inc. Greenhouse gases warm the lower atmosphere  Greenhouse gases differ in their ability to cause warming  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 more potent than carbon dioxide  Nitrous oxide is 298 times more potent than carbon dioxide

© 2014 Pearson Education, Inc. Greenhouse gases warm the lower atmosphere  Carbon dioxide is not the most potent greenhouse gas  It is present in the largest concentrations  It exerts six times more impact than methane, nitrous oxide, and halocarbons combined

© 2014 Pearson Education, Inc.

Characterize human influences on the atmosphere and on climate.  By burning fossil fuels and clearing forests, people are increasing atmospheric concentrations of greenhouse gases.  Increased greenhouse gas emissions enhance the greenhouse effect.  Input of aerosols into the atmosphere exerts a variable but slight cooling effect.

© 2014 Pearson Education, Inc. Greenhouse gas concentrations are rising fast  T he greenhouse effect is a natural phenomenon  Greenhouse gases have always been in the atmosphere  We are not worried about the natural greenhouse effect  Anthropogenic intensification is of concern  We have added new gasses (CFCs) and increased concentrations of others  Human activities increased atmospheric CO 2 from 280 parts per million (ppm) to 396 ppm in 2013  The highest levels in more than 800,000 years  Likely the highest in 20 million years

© 2014 Pearson Education, Inc.

Greenhouse gas concentrations are rising fast  Most carbon is stored in the upper lithosphere  Deposition, partial decay, and compression of organic matter led to formation of coal, oil, and natural gas  These deposits remained buried for millions of years  Burning fossil fuels transfers CO 2 from lithospheric reservoirs into the atmosphere  The main reason atmospheric carbon dioxide concentrations have increased so dramatically

© 2014 Pearson Education, Inc. Greenhouse gas concentrations are rising fast  Deforestation contributes to rising atmospheric CO 2  Forests serve as reservoirs for carbon  Removing trees reduces the carbon dioxide absorbed from the atmosphere

© 2014 Pearson Education, Inc.

Greenhouse gas concentrations are rising fast  Methane levels have increased 2.5-fold since 1750  Highest level in over 800,000 years  Released by tapping into fossil fuel deposits and from livestock, landfills, and crops such as rice  Nitrous oxide has increased nearly 20% since 1750  Produced by feedlots, chemical manufacturing plants, auto emissions, and synthetic nitrogen fertilizers

© 2014 Pearson Education, Inc. Greenhouse gas concentrations are rising fast  Tropospheric ozone levels have risen 36%  Halocarbon gases (CFCs) are declining  Water vapor is the most abundant greenhouse gas  Contributes most to the natural greenhouse effect  Concentrations have not changed

© 2014 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

© 2014 Pearson Education, Inc. Radiative forcing expresses change in energy input  Radiative forcing  the amount of change in thermal energy that a given factor causes  Positive forcing warms the surface  Negative forcing cools it  Pre-industrial Earth in 1750 was in balance—it had the same amount of energy entering as leaving  Earth is experiencing radiative forcing of 1.6 watts/m 2 more than it is emitting to space  Enough to alter the climate

© 2014 Pearson Education, Inc.

Feedback complicates our predictions  Tropospheric warming will transfer more water to the air  The effects of increased water vapor are uncertain. Two possible feedback loops could result  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 …less evaporation  Because of the feedback loops, minor modifications of the atmosphere can lead to major effects on climate

© 2014 Pearson Education, Inc. Climate varies naturally for several reasons  Milankovitch cycles  periodic changes in Earth’s rotation and orbit around the sun  Alter the way solar radiation is distributed over Earth  Modify patterns of atmospheric heating, triggering climate variation: periods of cold and ice (glaciation) and warm interglacial times  Solar output: the sun varies in the radiation it emits  Variation in solar energy has not been great enough to change Earth’s temperature  Radiative forcing is 0.12 watts/m 2 —much less than human causes  Solar radiation has been decreasing since 1970

© 2014 Pearson Education, Inc.

Climate varies naturally for several reasons  Ocean absorption: the ocean holds 50 times more carbon than the atmosphere  Gas dissolves directly in ocean water  Not absorbing as much CO 2 as we are emitting  Slowing, but not preventing, global warming  Warmer oceans absorb less CO 2  Rate of CO 2 absorption is slowing down  A positive feedback effect that accelerates warming

© 2014 Pearson Education, Inc. Ocean circulation  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  Moves 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