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mcb.berkeley.educoursesmcb31Lect22-23.ppt

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					Global Warming - Evidence
  Warming of the climate
system is unequivocal, as is
      now evident from
 observations of increases
  in global average air and
     ocean temperatures,
    widespread melting of
   snow and ice, and rising
  global average sea level.
         IPCC 2007
       Changes in Air Temperature Over the Past 400,000 Years




   Temperature deduced from isotopic analysis of Antarctic ice cores.
An ice core is a sample from the accumulation of snow and ice over many
years that have re-crystallized and have trapped air bubbles from previous
time periods. The composition of these ice cores, especially the presence of
hydrogen and oxygen isotopes, provides a picture of the climate at the time.
Because water molecules containing heavier isotopes have a lower vapor
pressure, when the temperature falls, the heavier water molecules condense
faster than the normal water molecules. The relative concentrations of the
heavier isotopes in the condensate indicate the temperature at the time.
                                                                                     7 Ma
                                                                chimpanzee



                                                                    “human”
                                                                                     5 Ma
 The genus
   Homo

Homo habilis

                                        Homo erectus
                                                                                     3 Ma
               Neanderthal



                 “human”
                                                                                     1 Ma


                             mitochondrial eve             speech    Y-chrom Adam

                             Homo sapiens




                                                       migration to Europe      agriculture
                                                   migration to S. Asia
Eleven of the last twelve years (1995 -2006) rank among the 12 warmest years
in the instrumental record of global surface temperature (since 1850). In the
last 100 years we’ve gained 0.74 °C. The warming trend over the last 50 years
(0.13 °C per decade) is nearly twice that for the last 100 years.
Loss of glaciers
Comparison photos
    showing the
     decline of
 Pedersen Glacier
  in Kenai Fjords
   National Park,
      Alaska.
 Comparison photos of Muir
     and Riggs Glaciers in
  Glacier Bay National Park
 and Preserve, Alaska. Muir
glacier, parts of which were
   greater than 65 meters
thick in 1941, has retreated
  out of the image in 2004
  (towards the upper left).
The distance to the visible
Riggs glacier in 2004 is ~3
 km. During this time, the
  Muir Glacier retreated
 more than 20 km (Benson
     and Field 1995).
Whitechuck glacier
  Washington



          About 1930




               2005
 This image shows the termini of the glaciers in the Bhutan-Himalaya. Glacial
lakes have been rapidly forming on the surface of the debris-covered glaciers
   in this region during the last few decades. There is a strong correlation
      between increasing temperatures and glacial retreat in this region.
                               QuickTime™ and a
                      TIFF (Uncompressed) decompressor
                         are neede d to see this picture.




The loss of glaciers is a general, not isolated, phenomenon
       that has been accelerating in recent years.
The Greenland icecap contains 1/8th of the total global ice-mass.
 The Greenland icecap
 is rapidly thinning at
    lower elevations

If the entire 2.85 million
km³ of ice were to melt,
 global sea levels would
   rise 7.2 m (23.6 ft)

   Recently, fears have
   grown that continued
    global warming will
    make the Greenland
     Ice Sheet cross a
      threshold where
   long-term melting of
      the ice sheet is
         inevitable.
Surface river of
meltwater on the
Greenland icecap
 plunging into a
 vertical chute.
 An area of Arctic sea ice the size of
Florida has melted away in just the last
 six days as melting at the top of the
   planet continues at a record rate.
        - ABC News 9/10/2007
  Arctic Sea ice reached
record lows in September,
  2007. The Northwest
 Passage opened for the
first time during satellite
        recordings.
  This satellite image
    shows the 2002
    breakup of the
Larsen B Ice Shelf in
comparison of the US
    state of Rhode
  Island. This region,
        covering
 approximately 3250
 km2 with 200 meter
  thick ice, had been
continuously glaciated
 since before the end
   of the last glacial
period (Domack et al.
         2005).
On February 28, 2008 a
part of the Wilkins Ice
Shelf collapsed and was
 “hanging by a thread”.
This area is about three
   times the area of
      Manhattan.
Sea level measurements from 23 long tide gauge records in
 geologically stable environments show a rise of around 20
           centimeters per century (2 mm/year).
       CO2 and Global Warming

 In 1896, a Swedish chemist, Svante Arrhenius
  predicted that changes in CO2 concentration
      could substantially alter the surface
     temperature of the earth through the
               greenhouse effect.

 Although the motivation for his work was an
explanation of the ice ages, he did predict that
 human emissions of CO2 would lead to global
 warming, though he thought that would be a
                positive change.


 His ideas were not generally accepted, in part
because there was not enough understanding of
the climate and the effects of photosynthesis
    and absorption of CO2 into the oceans.
   Greenhouse gases like
carbon dioxide, water and
methane naturally blanket
   the Earth and keep it
about 33° C warmer than
it would be without these
 gases in the atmosphere.
  This is called the green
       house effect.



Light from the sun is not
absorbed by these gases,
but a portion of the heat
coming from the surface
of the earth is absorbed
    by the gases and
     reradiated in all
directions, trapping some
    of the heat in our
       atmosphere.
       CO2 and Global Warming

 In 1896, a Swedish chemist, Svante Arrhenius
  predicted that changes in CO2 concentration
      could substantially alter the surface
     temperature of the earth through the
               greenhouse effect.

 Although the motivation for his work was an
explanation of the ice ages, he did predict that
 human emissions of CO2 would lead to global
 warming, though he thought that would be a
                positive change.


 His ideas were not generally accepted, in part
because there was not enough understanding of
the climate and the effects of photosynthesis
    and absorption of CO2 into the oceans.
Keeling’s accurate measurements over the last 50 years
 demonstrated that CO2 concentrations were actually
         increasing as Arrhenius had predicted.
* Global atmospheric concentrations of carbon dioxide, methane,
and nitrous oxide have increased markedly as a result of human
activities since 1750 and now far exceed pre-industrial values
over the past 650,000 years - IPCC, 2007
Variations in CO2
concentration in
the atmosphere
 during the last
 400 thousand
    years as
 measured from
   ice cores.




                     Since the Industrial Revolution, circa 1800, the burning of fossil fuels
                    has caused a dramatic increase of CO2 in the atmosphere, reaching levels
                       which are likely unprecedented in the last 20 million years [1]. This
                       increase has been implicated as a primary cause of global warming.
The timescales for removal of
emitted carbon dioxide from
the atmosphere. Mixing in the
biosphere and oceans removes
70-85% of emissions after 200
years, but the remainder
establishes a new equilibrium
that may persist for hundreds
of thousands of years.
                       Climate Change Summary

* Warming of the climate system is unequivocal.
* Most of the increase in global temperatures since the mid-20th century is
  due to the increased concentration of anthropogenic greenhouse gases.
* Anthropogenic warming and sea level rise will continue for centuries even if
  greenhouse gas concentrations are stabilized.

* The probability that this is caused by natural climatic processes alone is
  less than 5%.

* World temperatures will rise by 1.1 and 6.4 °C during the 21st century.
* Sea levels will probably rise by 18 to 59 cm (7.08 to 23.22 in).
* There will likely be more frequent warm spells, heat waves and heavy
  rainfall (>90% chance).

* There will probably be an increase in droughts, tropical cyclones and
  extreme high tides (>66% chance).

                                                     Slightly edited from IPCC 2007

				
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posted:12/11/2012
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