Observations of climate change

1
Lecture 16

• Observations of climate change
• Feedback mechanisms
• Air pollution
• The stratospheric ozone hole
• Changing land surfaces
• Greenhouse gases and global warming
• Global warming and H2O
• Climate modeling
• Climate change assessments

2
Global average surface temperature
3
ive/-ive feedback mechanisms

• Feedbacks occur when one change leads to some
  other change that can act to reinforce or inhibit
  the original change
• Reinforcing, ive feedback, e.g. water vapor
  feedback, ice/albedo feedback
• Inhibiting, ive feedback. Example CO2 and
  photosynthesis end result is equilibrium

4
Ice albedo temperature feedback
5
Air pollution (aerosols and gases that are
harmful to life)

• Natural sources e.g., from volcanoes, soils
• Anthropogenic sources
• Carbon monoxide
• Lead
• Sulfur dioxide, sulfur trioxide (H2O)
• Sulfuric acid
• Nitric oxide, nitrogen dioxide
• hydrocarbons, (volatile organic compounds)
• ozone

6
The stratospheric ozone hole

• Ozone produced photochemically in the
  stratosphere
• Ozone plays a fundamental role in the radiation
  budget and dynamics of life
• Minimum amount of ozone is observed in spring in
  SH (October). Why?
• Discussed ozone depletion as a result of release
  of CFCs.

7

• The winter atmosphere above Antarctica is cold,
  -90C.
• Strong temperature gradient from pole to
  mid-latitudes. From thermal wind arguments, this
  results in strong westerly winds encircling the
  South Pole, so called polar vortex
• Results in isolation of SP air, keeping it very
  cold and chemically isolated
• Polar stratospheric clouds can form
• Add sunlight and the result is rapid destruction
  of ozone

8
Total column ozone over Halley Bay station
Notice change after 1975
9
Oct monthly mean ozone concentration
87, 89, 90, 91
10
Why not a NH ozone hole?

• The NH polar vortex is continually being
  bombarded with Rossby waves that have propagated
  from the troposphere in the NH. This disturbs
  the vortex and does not allow the same chemical
  isolation (nor as strong a vortex) as occurs in
  the SH.

11
Stratospheric polar vortex
12
WMO Scientific assessments of ozone depletion
2002, 1998, 94, 91, 89, 85
13
Life cycle of CFCs Cl and Br compounds in the
atmosphere cause the ozone depletion over
Antarctica
14
Changing land surfaces

• Desertification spreading of a desert region
  because of a combination of climate change and
  human impacts on the land. Examples
  overgrazing, deforestation without reforestation,
  diversion of water away from a formerly fertile
  region, farming on land with unsuitable terrain
  or soil

15

• The Sahel or sub-Sahara (14-18N)
• Partly due to natural variability depends on
  the northernmost location of the ITCZ for rain.
  Shifts by 100 km from year to year
• Enhanced by biogeophysical ive feedback mechanism

16
The incredible shrinking Aral Sea
1973
1987
2000
17
Urban heat island effect
18
Notice the warmth of Pittsburgh compared to the
surrounding rural area
19
Greenhouse gases and global warming

• H2O, CO2, CH4, CFCs are all gh gases
• Humans have changed the amount of gh gases in the
  atmosphere over the past century by 25
• Based on the radiation concepts of the greenhouse
  effect, temperature should have increased a lot
  too. Hard to quantify
• Complex system

20
Global warming and atmospheric water

• Human activities add little H2O to the atmosphere
  directly
• Saturation water pressure increases very rapidly
  with temperature
• Since H2O is a strong gh gas this will lead to
  still warmer temperatures, still more water vapor
  etc
• On the other hand cloudiness may also increase,
  which would be a cooling effect

21
Global warming and atmospheric H2O, continued

• More aerosols can mean more CCN, more droplets
  can form in clouds and the clouds may reflect
  more
• Indirect aerosol effect on climate
• Contrails are airplane-induced clouds

22
Stratus clouds off California, ship tracks can be
seen in the clouds since their reflectance is
enhanced by increased aerosols
23
Climate modeling

• GCMs, global climate models consist of an
  atmospheric model, coupled to an ocean model,
  coupled to a sea ice m., land surface model
• Give statistical estimates of future conditions
• Sensitivity studies to understand processes

24
Schematic of atmospheric processes included in a
GCM