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MET 112 Global Climate Change – Lecture 7
Observations of
Recent Climate Change
Dr. Craig Clements
San Jose State University
Outline
 How do we observe?
 Recent trends in temperature
 Recent trends in GHGs
What does ‘to observe’ mean?
- to watch and record.
Where do our observations come from?
 Measurements
– Of what?
 Who compiles these measurements for
governments and society?
 IPCC:
Intergovernmental Panel on Climate Change
www.ipcc.ch
Temperature stations
Change in surface temperature in 20th century
Bubbles Trapped in ice core
Petit, Jean-Robert, et al (1999). “Climate and atmospheric history of the past
420,000 years from the Vostok ice core, Antarctica”. Nature 399: 429-436.
Ice Core layers
•GISP2 ice core (Greenland Summit)
•Archived at the National Ice Core Laboratory in CO.
•from 1837-1838 meters in which annual layers are clearly visible.
•The appearance of layers results from differences in the size of
snow crystals deposited in winter versus summer
•Counting such layers has been used (in combination with other
techniques) to reliably determine the age of the ice.
•This ice was formed ~16250 years ago during the final stages of
the last ice age and approximately 38 years are represented here.
Ice Cores
Coring Earth’s ice sheets
Coring mountain glaciers
Time Series Analysis: Examples of Temperature
Change
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Trends
Periodic Oscillations
Random Variations
Jumps
Examples of Temperature Change

Draw the following:
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend + Oscillation
Random variations
Random + trend
Jump
Random + jump
Trend
Temperature
0
20
40
Time
60
80
100
This graphs represents
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
1.
2.
3.
4.
5.
6.
7.
0
20
40
Time
60
80
1
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
1.
2.
3.
4.
5.
6.
7.
Trend
Oscillation
Trend+Oscillation
Random variation
Random+Trend
Jump
Random+Jump
Temperature
This graphs represents
0
20
40
Time
60
80
100
Time series of
climate data
Time series of
climate data
Time Frames -- Examples
 Seconds to minutes – Small-Scale Turbulence
 Hours – Diurnal Cycle (Caused by Earth’s
Rotation)
 Hours to Days – Weather Systems
 Months – Seasonal Cycle (Caused by tilt of
axis)
 Years – El Niño
 Decades -- Pacific Decadal Oscillation
 Centuries – Warming during 20th Century
(Increase in greenhouse gases?)
 Tens of thousands of Years – Irregularities in
Earth’s motions
 Millions of Years – Geologic Processes
Time Series Data: High Frequency (10 Hz = 10 samples/sec)
Latest global temperatures
Temperature over the last 10 years
…“Over the last 140 years, the best estimate is that the
global average surface temperature has increased by
0.7 ± 0.2°C” (IPCC 2007)
 So the temperature trend is:
0.7°C ± 0.2°C
 What does this mean?
 Temperature trend is between 0.8°C and 0.4°C
 The Uncertainty (± 0.2°C ) is critical component to the
observed trend
Current CO2: ~383 ppm
What Changed Around 1800?
 Industrial Revolution
– Increased burning of fossil fuels
 Also, extensive changes in land use began
– the clearing and removal of forests
Ice core record
Increase in ocean temperature causes a decrease
in the solubility of CO2 in sea water (outgassing),
which increases the atmospheric loading of CO2
(Stott et al. 2007).
In the Vostok Ice core, carbon dioxide
concentrations lagged behind the temperature by
about 600±400 years (Caillon et al. 1999).
What caused the large temperature changes?
Three cycles of the Earth’s orbit: called Milankovitch cycles
Milankovitch cycles: Eccentricity
Earth’s orbit around the Sun (Earth-Sun Distance)
The closest point to the Sun in a planet's orbit
is called perihelion. The furthest point is called aphelion.
1. Eccentricity: “off-centerdness” of the orbit varies over time
in a complicated way.
• Net result: two main cycles– one averages ~100,000 years
and another about 400,000 years.
• When eccentricity is low there is little change through the
year in the Earth-Sun distance.
• When eccentricity is high-the sunlight reaching Earth is ~20%
stronger at perihelion than at aphelion.
Earth’s orbit around the Sun
Eccentricity
off-centerdness” of the orbit
Milankovitch cycles: Obliquity of the Earth’s Axis
Earth’s tilt: ranges from ~21.8º to 24.4º and changes
over the course of ~41,000 years
When the tilt is most pronounced, it allows for stronger
summer Sun and weaker winter Sun– especially at
high latitudes.
Ice ages often set in as the tilt decreases:
Because the progressively cooler summers can’t melt
the past winter’s snow. At the other extreme, it can
bring the Earth out of an ice age.
Milankovitch cycles: Precession of Earth’s Axis of
Rotation.
Precession: Angular motion (wobble) of the Earth’s
axis of rotation.
- varies ~26,000 years.
0º
Precession
earth
Obliquity
Ice core CO2 record
Retreat of mountain glaciers: ‘visual inspection’
Boulder Glacier, Mt. Baker, Washington
Retreat of mountain glaciers
Melting of Greenland Icesheet
Global rise in sea level last 20,000 years
Global rise in sea level in the 20th century
Shorter winters in Alaska
Latest global temperatures
Instrumental Air Temperature Record
 Averaged by decade
45
Current CO2: ~383 ppm
What Changed Around 1800?
 Industrial Revolution
– Increased burning of fossil fuels
 Also, extensive changes in land use began
– the clearing and removal of forests
Burning of Fossil Fuels
 Fossil Fuels: Fuels obtained from the earth
are part of the buried organic carbon
“reservoir”
– Examples: Coal, petroleum products,
natural gas
 The burning of fossil fuels is essentially
– A large acceleration of the oxidation of
buried organic carbon
Land-Use Changes
 Deforestation:
– The intentional clearing of forests for
farmland and habitation
 This process is essentially an acceleration of
one part of the short-term carbon cycle:
– the decay of dead vegetation
 Also causes change in surface albedo
(generally cooling)
Greenhouse Gases
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Carbon Dioxide
Methane
Nitrous Oxide
CFCs (Chlorofluorocarbons)
Others
Methane
Anthropogenic Methane Sources
 Leakage from natural gas pipelines and coal
mines
 Emissions from cattle
 Emissions from rice paddies
Nitrous Oxide N2O
Anthropogenic Sources of Nitrous
Oxide
 Agriculture
 Bacteria in Soils
 Nitrogen fertilizers
CFCs (Chlorofluorocarbons)
CFC-11
CFC-12
Sources of CFCs
 Leakage from old air conditioners and
refrigerators
 Production of CFCs was banned in 1987
because of stratospheric ozone destruction
– CFC concentrations appear to now be
decreasing
– There are no natural sources of CFCs
The Land and Oceans have both warmed
Precipitation patterns have changed