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Dr. Michael MacCracken Is Climate Enginering an Option for Dealing with Climate Change? 9/25/09

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Title: Greenhouse Effect Climate Change Global Warming Author: James Fleming Last modified by: James Fleming Created Date: 9/29/2009 4:09:36 AM Document presentation ... – PowerPoint PPT presentation

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Title: Dr. Michael MacCracken Is Climate Enginering an Option for Dealing with Climate Change? 9/25/09


1
Dr. Michael MacCracken Is Climate Enginering an
Option for Dealing with Climate Change? 9/25/09
  • http//www.colby.edu/sts/20090925MaccrackenGeoengi
    neeringColby.pdf

2
Why the Earth has Seasons
3
Seasons
  • A season is a period of time during the calendar
    year characterized by or associated with a set of
    coherent weather or climate phenomena.
  • Seasons are terrestrial responses to solar
    heating inequalities that are governed by the
    tilt of the Earths axis and the shape of its
    orbit around the Sun.

4
Basic Earth-Sun Geometry
  • Fig 3.5

5
Angle and Duration of Sunlight
  • Angle of the suns rays changes over the course
    of the year.
  • In our latitude, the noontime sun angle varies
    from 68.5o on June 21 to 21.5o on December 21
  • Duration of the day changes over the course of
    the year.
  • Above the Arctic circle, the duration of the day
    on June 21 is 24 hours on December 21 it is 0
    hours.

6
ANGLE Earth from Space, June 21 Fig. 3.6
suitably tilted
7
Duration
8
Other Factors
  • The fact that the Earths orbit is not a perfect
    circle makes little difference at all.
  • The Earth is farther from the Sun in summer in
    the Northern Hemisphere (aphelion on July 5) and
    closer to the Sun in the Winter (perihelion on
    Jan. 5).
  • The difference of 3.5 in distance results in 7
    greater solar insolation in Winter than Summer.
  • Overall, the angle and duration factors far
    outweigh this difference in distance.
  • Moreover, Summer is actually longer than Winter!
    There are 185 days between March 21 and Sept. 22
    but only 180 days between Sept. 22 and March 21.
  • Why?

9
Basic Earth-Sun Geometry
  • Fig 3.5

10
Annual Radiation Surplus and Deficit as a
Function of Latitude
11
Greenhouse Effect Climate Change Global
Warming READ Somerville Chapter 3
12
Is the Greenhouse Effect Real?
  • YES!
  • Without greenhouse gases in the atmosphere (CO2
    and H2O) the Earth would be about 33 degrees
    cooler than at present
  • The average global temperature is now 287 K
  • Without greenhouse gases it would be 254 K
  • We would have an ice-covered planet!

13
The Greenhouse Effect
14
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15
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16
Is the Climate Changing?
  • YES!
  • It has always been changing!
  • And it is expected to continue to change

17
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18
Temperature Trends, 1850-1995
19
What is Humanity Doing to Enhance the Natural
Greenhouse Effect?
  • The composition of the earth's atmosphere is
    undergoing a major global change
  • Human activities, such as air pollution,
    deforestation, the burning of fossil fuels, and
    even agricultural practices are now starting to
    alter the balance of radiatively active gases in
    our atmosphere

20
Atmospheric CO2 concentrations
21
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