Ozone Hole

1
Ozone Hole

• 1985, British scientists reported a sudden large
  depletion in the Ozone over the south pole
• Simultaneous satellite measurements confirmed the
  decrease, but were rejected by the processing
  software-the decrease seen was so large it was
  rejected by the data quality control algorithms.
• When the data were re-run through the processing
  programs without the data quality flags, the
  ozone hole had been seen all the way back to 1976!

2
Causes

• Unique set of conditions in the atmosphere at
  the south pole.
• Polar Stratospheric Clouds (PSC) are clouds in
  the winter polar stratosphere at altitudes of
  15,00025,000 meters (50,00080,000 ft).
• Due to their high altitude and the curvature of
  the surface of the Earth, these clouds will
  receive sunlight from below the horizon and
  reflect it to the ground, shining brightly well
  before dawn or after dusk.
• PSCs form at very low temperatures, below -78 C.

3
PSCs and Ozone

• Ordinarily, most of the chlorine in the
  stratosphere resides in stable "reservoir"
  compounds, primarily hydrochloric acid (HCl) and
  chlorine nitrate (ClONO2).
• During the Antarctic winter and spring, reactions
  on the surface of the polar stratospheric cloud
  particles convert these "reservoir" compounds
  into reactive free radicals (Cl and ClO).
• The clouds can also remove NO2 from the
  atmosphere by converting it to nitric acid, which
  prevents the newly formed ClO from being
  converted back into ClONO

4
What is being done

• 1976 Report by the National Academy of Science
  that there was credible scientific evidence for
  ozone depletion
• US and several other countries banned the use of
  CFC in aerosol spray cans
• 1985 Vienna Convention for the Protection of the
  Ozone Layer signed
• Established a framework for the negotiation of
  international agreements regulating ozone
  depleting substances
• 1987 Montreal Protocol is signed by 43 nations
• Froze CFC production at 1986 levels and reduce it
  to 50 by 1999
• Follow up meeting in London modified it to to
  phase out CFCs entirely by 2000
• This date was moved up to 1996 in 1992
• CFCs replaced now by HCFCs or HFC (which are
  greenhouse gases)
• Most commonly used in the US is HFC-134a (R-134a)
  which has replaced CFCs in automobile air
  conditioners

5
Effect of these initiatives

• Atmospheric concentrations have been declining
• Antarctic Ozone hole will continue for decades
• Expected to see Ozone concentrations increase by
  5-10 in the lower stratosphere by 2020
• A return to pre 1980 levels is expected by
  2060-2075.
• Eventual complete recovery of the ozone will
  occur
• Delays will be the result of developing countries
  which employ CFCs

6
Global Warming

• The name given to the increase in the average
  temperature of the Earths near surface
  temperature and oceans that has occurred since
  the middle of the 20th century.
• In the graph to the right, panel a gives the
  Earth's surface temperature is shown year by year
  (red bars) and approximately decade by decade
  (black line, panel b gives the year by year (blue
  curve) and 50 year average (black curve)
  variations of the average surface temperature of
  the Northern Hemisphere for the past 1000 years
  have been reconstructed from "proxy" data
  calibrated against thermometer data.

7
Greenhouse effect

• Main culprit behind global warming
• Sunlight enters the atmosphere and warms the
  Earth (UV, visible, IR)
• At night, Earth radiates heat energy it gained
  during the day(mostly at IR wavelengths)
• Not all of this energy escapes the
  atmosphere-some of it is absorbed and re-emitted
  back into the atmosphere, warming the atmosphere
  and the Earth.
• Not necessarily a bad thing-without it the Earth
  would be cold and life (a least as we know it)
  would not be possible

8
Venus

• Hottest planet in the solar system
• But not the closest to the sun
• Atmosphere is 96.5 carbon dioxide
• Venus once had immense amounts of water, but no
  ozone layer-the UV radiation broke up the water
  molecules
• Unfortunate, water absorbs carbon dioxide wand
  mitigates the greenhouse effect
• Resulted in an extreme greenhouse effect

9
Greenhouse effect-What could happen

• Global temperatures rise until boiling point of
  water is reached
• As water boils away, it becomes water vapor in
  the atmosphere, accelerating the heat rise
  (called positive feedback).
• At a few hundred degrees celsius, carbon dioxide
  would be released from the rocks (sublimation),
  accelerating the heating again
• Eventually the Earth would stabilize at surface
  temperatures similar to Venus (T860F)
• Worst case, not realistic scenario

10
Greenhouse Gasses in order of importance

• water vapor
• carbon dioxide
• methane
• nitrous oxide
• ozone
• CFCs

11
Changes in greenhouse gas concentrations

• Historical variations can be tracked via analysis
  of ice cores
• Ice core - a core sample (a cylindrical section
  of a naturally occurring medium consistent enough
  to hold a layered structure) 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 provides a
  picture of the climate at the time.
• Record for over 800,000 years

Gas Preindustrial Level
Current Level Increase since 1750 Carbon
dioxide 280 ppm 387ppm
104 ppm Methane
700 ppb 1,745 ppb
1,045 ppb Nitrous oxide 270 ppb
314 ppb 44 ppb CFC-12
0
533 ppt 533 ppt
12
What do the ice cores tell us?

• Natural variations occur in the greenhouse gas
  concentrations

13
Post industrial revolution
14
Man made sources of greenhouse gasses

• Also called Anthropogenic, which designates an
  effect or object resulting from human activity
• burning of fossil fuels and deforestation
  leading to higher carbon dioxide concentrations.
• Account for one third of total anthropogenic CO2
  emissions.
• livestock enteric fermentation and manure
  management, paddy rice farming, land use and
  wetland changes, pipeline losses, and covered
  vented landfill emissions leading to higher
  methane atmospheric concentrations. Many of the
  newer style fully vented septic systems that
  enhance and target the fermentation process also
  are sources of atmospheric methane.
• use of chlorofluorocarbons (CFCs) in
  refrigeration systems, and use of CFCs and halons
  in fire suppression systems and manufacturing
  processes.
• agricultural activities, including the use of
  fertilizers, that lead to higher nitrous oxide
  (N2O) concentrations.

15
What are we seeing?

• Since 1860-1900, global surface temperatures have
  increased by 1.35 F
• Urban heat island effect only accounts for 0.02 C
  rise
• Since 1979 land T have increased twice as fast as
  ocean temperatures
• Temperatures on the lower troposphere have have
  increased by 0.62 between 1979 and 2000.

16
Hold on, could it be the sun?

• No overall increase in solar brightness in over
  1000 years
• Solar cycles do cause small variations in
  brightness, but not enough to account for what
  has been seen
• No its not the sun

17
Feedback-making the problem worse (or better)

• Positive feedback-when the warming induces
  further warming
• Negative feedback when the warming induces a
  cooling