MET 112 Global Climate Change – Lecture 7
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 20 th 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.

• 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.

Coring Earth’s ice sheets

Coring mountain glaciers

Time Series Analysis: Examples of Temperature
Change
 Trends
 Periodic Oscillations
 Random Variations
 Jumps

 Draw the following:
1. Trend
2. Oscillation
3. Trend + Oscillation
4. Random variations
5. Random + trend
6. Jump
7. Random + jump

0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

1. Trend
2.
Oscillation
3. Trend+Oscillation
4.
Random variation
5.
Random+Trend
6.
Jump
7.
Random+Jump
0 20 40
Time
60 80 100

Time series of climate data

Time series of climate data

 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 20 th 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)

…“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 CO
2
: ~383 ppm

 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 CO
2 in sea water (outgassing), which increases the atmospheric loading of CO
2
(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 offcenterdness” 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.

Precession
0 º earth
Obliquity

Ice core CO
2 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 20 th century

Shorter winters in Alaska

Instrumental Air Temperature Record
 Averaged by decade
45

Current CO
2
: ~383 ppm

 Industrial Revolution
– Increased burning of fossil fuels
 Also, extensive changes in land use began
– the clearing and removal of forests

 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

 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)

 Carbon Dioxide
 Methane
 Nitrous Oxide
 CFCs (Chlorofluorocarbons)
 Others

 Leakage from natural gas pipelines and coal mines
 Emissions from cattle
 Emissions from rice paddies

2

 Agriculture
 Bacteria in Soils
 Nitrogen fertilizers

CFCs (Chlorofluorocarbons)
CFC-11
CFC-12

 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