Climate Drivers Global Change Ecology Botany 275

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Climate Drivers Global Change Ecology Botany 275
Climate Drivers
Global Change Ecology
      Botany 275
Climate Drivers Global Change Ecology Botany 275
External and Internal
 Drivers of Climate

   External Drivers
     -Sunspot Cycles
     -Orbital Variations
   Internal Drivers
     -Plate Tectonics
     -Volcanic Activity
     -Albedo
     -Greenhouse Effect
Climate Drivers Global Change Ecology Botany 275
Climate forcing mechanisms

Mechanism                               Time period
1. Solar Forcing
     Solar intensity (sunspots)         (10 s to 100 s of years)
     Orbital Variations                 (Thousands of years)
2. Plate Tectonics                      (Millions of years)
     Mountain building, continent locations
3. Albedo                               (all time scales)
4. Aerosols                             (1-10 years)
     Volcanoes, pollution
5. Greenhouse Effect                     (all time scales)
     CO2, Methane, Water vapor
6. Land use                             (1 to 100 s of years)
Climate Drivers Global Change Ecology Botany 275
Climate Drivers
Incoming solar energy
Climate Drivers Global Change Ecology Botany 275
Radiative

           Forcing of Climate Change

Measured

 in units of watts per square meter (watts/m2)

Average solar radiation reaching the earth at the top of
the atmosphere=1370 watts/m2
This equates to 343 watts/m2 when distributed
uniformly over the earth s surface.

For reference: A doubling of CO2 from pre-industrial
level of 280 ppmv to 560 ppmv results in radiative
forcing of about 4 watts/m2,
Climate Drivers Global Change Ecology Botany 275
Estimated solar irradiance variations
                   1750-2000
One way to measure
solar intensity is from
satellite observations,
which are available only
since the late 1970 s.
These show solar
variations of about 0.2
watts/m2. This graph
shows estimates of
changes in solar output
since 1750.
Climate Drivers Global Change Ecology Botany 275
Figure 2.17
Climate Drivers Global Change Ecology Botany 275
Figure 2.16
Climate Drivers Global Change Ecology Botany 275
Sunspots
Climate Drivers Global Change Ecology Botany 275
Sunspot Cycles
Number of sunspots

                                      Maunder
Climate Drivers
Orbital Variations or Milankovitch
              Cycles
Milutin Milankovitch 1879-1958

     http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
Current Eccentricity
Variation in Axial Obliquity, 40,000 year cycle
 Tilt of the axis

                http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
Precession of the equinoxes, ~19,000 to 23,000 year
Cycle: Direction of tilt Wobbling top

             http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
Orbital Variations:
   Milankovitch Cycles

Orbital Eccentricity. Shape of the
Earth s orbit (cycles ~100,000
years) – changes the distance
between the Earth and Sun

Axial tilt (cycles over 41,000
years) – changes noon day Sun
elevation and daylength

Precession of the equinoxes
(cycles over 19,000-23,000 years)
– changes when winter and
summer occur on Earth.
Insolation at 65 degrees north latitude
from the present to 1 million years ago

                              Berger 1991
Vostok time series and insolation

                                        Atm
                                       Temp
Question:
1. How do Milankovitch cycles (e.g.,
   changes in orbital parameters) lead
   to the onset and termination of ice
   ages? (e.g., warm summers & cold winters,
   cool summers and warm winters, etc.)

2. Propose a sequence of events or
   processes considering that the
   overall change in insolation is small
   (e.g., ~0.25 watts/m2), but that the
   ice ages are global.
-35
                                                               GISP2
                                                               (N. Atlantic SSTs)
per mille
VSMOW

            700                                                Methane
      -45
            ppbv
                                                               CO2
      275
            400

   ppmv     100
                                                               Sea-Level
                                                               (Ice Volume)
             m
     175

       50                                   July (45 deg. N)
             0
                        warm

    W/m2                                                       Insolation

                        cold

            January (45 deg. N)
      -50
                   25        20  15       10     5    0
                                Calendarof
                            Thousands    ka years ago
-35
                                                               GISP2
                                                               (N. Atlantic SSTs)
per mille
VSMOW

              700                                              Methane
        -45
              ppbv
                                                               CO2
       275
              400

   ppmv       100
                                                               Sea-Level
                      Small ice sheets

                      (Ice Volume)
               m
       175

 50            0                            July (45 deg. N)
                      Large ice sheets

      W/m2                                                     Insolation

                                            January (45 deg. N)
 -50
                     25      20  15       10     5    0
                                Calendarof
                            Thousands    ka years ago
-35
                                                             GISP2
                                                             (N. Atlantic SSTs)
per mille
VSMOW

            700                                              Methane
      -45
            ppbv
                                                             CO2 (from ice cores)
      275
            400             High CO2

   ppmv     100
                                                             Sea-Level
                                                             (Ice Volume)
             m
     175                Low CO2

       50    0                            July (45 deg. N)

    W/m2                                                     Insolation

                                          January (45 deg. N)
      -50
                   25     20  15       10     5    0
                             Calendarof
                         Thousands    ka years ago
GISP2
                      warm

         -35                                                      (Oxygen isotopes-
                                                                  Measures air
per mille                                                         temperature)
VSMOW

               700         cold

                                Methane
         -45
               ppbv
                                                                  CO2 (from ice cores)
         275
               400

     ppmv      100
                                                                  Sea-Level
                                                                  (Ice Volume)
                m
         175

    50          0                              July (45 deg. N)

  W/m2                                                            Insolation

                                              January (45 deg. N)
   -50
                      25        20  15       10     5    0
                                   Calendarof
                               Thousands    ka years ago
Milankovitch Theory of Ice Ages
The Milankovitch (1941) theory of the ice ages assumes that
summer insolation anomalies at high latitudes in the Northern
   Hemisphere (NH) drive the ice ages: minimum summer
   insolation allows snow and ice accumulated in the cold
 season to survive, while maximum summer insolation tends
                    to melt the ice sheets.

Hansen et al. 2007. Climate change and trace gases. Phil. Trans. R. Soc. A. 1925-1954.
Alternative Theory of Ice Ages
Hansen et al. 2007 suggest that spring is the critical season for
terminations, because the albedo feedback works via the large
   change in absorbed sunlight that begins once the ice/snow
 surface becomes wet, after which the surface albedo remains
 low until thick fresh snow accumulates. A spring maximum of
   insolation anomaly pushes the first melt earlier in the year,
 without comparable shortening of autumn melt, thus abetting
  ice sheet disintegration. And an increase of GHGs stretches
  the melt season both earlier and later, while also increasing
                         midsummer melt.

 Hansen et al. 2007. Climate change and trace gases. Phil. Trans. R. Soc. A. 1925-1954.
Figure 3. (a) Temperature, CO2, and sea level (SL), (b) late spring
 (April,May,June) insolation at 60 degrees N and (c) late spring (October,
            November, December) insolation at 75 degrees S.

Hansen et al. 2007. Climate change and trace gases. Phil. Trans. R. Soc. A. 1925-1954.
Could both theories contribute to
              glacial cycles?

 Perhaps the Milankovitch theory (summer/winter insolation)
could lead to the initial formation of ice sheets, but the Hansen
            theory leads to the sudden termination.
Vostok Ice Core

Hansen et al. 2007. Climate change and trace gases. Phil. Trans. R. Soc. A. 1925-1954.
Question:
1. The increase in temperature in the
   Vostok ice core seems to preceed
   CO2 rise by several hundred years.
   How do you account for this? What
   does this imply about the role of
   CO2?

2. How do would you respond to a
   sceptic that uses this result to argue
   that we therefore should not be
   concerned about rising CO2 levels?
Question:

1. How do would you respond to a
   sceptic that argues that solar output
   and sunspot activity control global
   temperatures (and therefore we
   should not be concerned about rising
   CO2 levels) ?
Solar forces have affected
   the climate system

 1
     Radiative forcing (W/m2)

 0

-1

-2

-3

-4
  1900                          1950   2000
Figure SPM.2
Question:
What is the role of external forcing
 likely to be in recent warming?
Question:
1. What seasonal distribution of
    insolation do you expect to lead to
onset and end of ice ages?

(e.g., warm summers & cold winters, cool summers
              and warm winters, etc.)

2. Why? Propose a sequence of events
or processes that explain and support
your answer to 1.
Variation in Orbital Eccentricity (~100,000 year cycle)

                                             perihelion

                                              aphelion

             http://earthobservatory.nasa.gov/Library/Giants/Milankovitch/
SPM 3
External and Internal
 Drivers of Climate

External
    -Sunspot Cycles (Decades)
    -Orbital Variations (Thousands of years)
Internal
    -Plate Tectonics (Millions of years)
    -Volcanic Activity (1-3 years)
    -Albedo (All time scales)
    -Greenhouse Effect (All time scales)
What is climate ?

•Climate is average
weather
     and its variability
     for a particular region
     over a period of time
  Climate is what we expect,
  weather is what we get.
What is climate change?
•Climate change is a shift in climate relative to a
given reference time period
•It is caused by:
        Natural factors
            -Solar variability
               -Volcanic dust levels
                   -Internal variability
                       -Geological change
         Human factors
            - Greenhouse gases
               - Aerosols
                  -Ozone depletion
                     -Land use change
Proxy data also indicate that the recent warming is
likely unprecedented in at least the past millennium

        Source: IPCC(2001)
Review
              FAQ 6.1, Figure 1

What are the periodicities associated with each orbital
variation?
Questions:
1. How do you expect orbital eccentricity
and precision to interact to affect
seasonal insolation?

2. How about obliquity and precision?

3. Under what conditions might we
expect most seasonal variation in
insolation?
Record of oxygen isotopes in ocean sediment over
 the last 800,000 years shows several glaciations
    (The last glaciation was 18,000 years ago)

                                      Warm (interglacial)

        Thousands of Years Ago
                                           Cold (glacial)
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