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MET 112 Global Climate Change - Lecture 4
Natural Climate ForcingDr. Eugene Cordero
San Jose State University
Outline – Earth’s early history Evolution of the atmosphere Temperature variations Activity
Articles we’ve been reading…
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In this weeks reading, the main topic of the article from New Zealand is about
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Tra
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Both
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Both
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1. Changes in CO2
2. Changes in CH4
3. Changes in solar radiation
4. Transport of oil
5. Transport of water
6. Changes in air pollution
7. Both 1 and 4
8. Both 1 and 5
9. Both 1 and 6
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Who is the primary funder of the American Enterprise Institute (AEI)
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1. NASA
2. ExxonMobil
3. Google
4. HP
5. PrimeAmerica
6. ESPN
7. CNN
Temperature Graph
Source:
http://www.ruf.rice.edu/~leeman/aNR.html
Water restrictions in Australia
Source:
http://www.melbournewater.com.au/content/water/water_storages/stage_3_water_restrictions_-_questions_and_answers.asp
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Natural Climate Change
External Forcing:–
Internal Forcing:–
The agent of change is outside of the Earth-atmosphere system
The agent of change is within the Earth-atmosphere system itself
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External Forcing
Variations in solar output
Orbital variations
Meteors
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Solar Variations
Sunspots correlate with solar activityMore sunspots, more solar energy
Sunspots are the most familiar type of solar activity.
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SOLAR ACTIVITY
Sunspots are the most familiar type of solar activity.
THE SOLAR CYCLE
Sunspot numbers increase and decrease – over an 11-year cycle
Observed for centuries. Individual spots last from
a few hours to months. Studies show the Sun is
in fact about – 0.1% brighter when
solar activity is high.
SOLAR INFLUENCES ON CLIMATE
Solar activity appears to slightly change the Sun’s brightness and affect climate on the Earth...
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THE MAUNDER MINIMUM
An absence of sunspots was well observed – from 1645 to 1715.
The so-called “Maunder minimum” coincided with a cool climatic period in Europe and North America: – “Little Ice Age”
The Maunder Minimum was not unique. Increased medieval activity
– correlated with climate change.
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Orbital changes
Milankovitch theory:
Serbian astrophysicist in 1920’s who studied effects of solar radiation on the irregularity of ice ages
Variations in the Earth’s orbit– Changes in shape of the earth’s orbit around sun:
Eccentricity (100,000 years)– Wobbling of the earth’s axis of rotation:
Precession (22,000 years)– Changes in the tilt of earth’s axis:
Obliquity (41,000 years)
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Earth’s orbit: an ellipse
• Perihelion: place in the orbit closest to the Sun
• Aphelion: place in the orbit farthest from the Sun
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Eccentricity: period ~ 100,000 100,000 yearsyears
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Precession: period ~ 22,000 years22,000 years
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Axis tilt: period ~ 41,000 years41,000 years
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Temperature: the last 400,000 yearsFrom the Vostok ice core (Antarctica)
Fig 4.5
High summer sunshine, lower ice volume
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Formation of Glaciers
Glaciers - composed of fallen snow that is compressed into a large, thickened mass of ice over many years
Glacier Growth: When over a year snowfall (winter) is larger than snowmelt (summer)
Glacier Decay: When over a year snowfall (winter) is less than snowmelt (summer)
Glacier growth and decay largely influenced by summer temperatures.
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Internal Forcing
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Ocean changes Chemical changes in the atmosphere (i.e. CO2)
– Natural variations
Plate tectonics/mountain building
Volcanoes
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Activity
Consider the fact that today, the perihelion of the Earth’s orbit around the sun occurs in the Northern Hemisphere winter. In 11,000 years, the perihelion will occur during Northern Hemisphere summer. A) Explain how the climate (i.e. temperature of summer compared to temperature of winter) of the Northern Hemisphere would change in 11,000 years just due to the precession.
B) How would this affect the presence of Northern Hemisphere glaciers (growing or decaying)? Assume growth is largely controlled by summer temperature.
If the earth’s tilt was to decrease, how would the summer temperature change at our latitude
War
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Summ
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Impo
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tell
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79%1. Warmer summer
2. Cooler summer
3. Summer would stay the same
4. Impossible to tell
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A: How would climate change
War
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win
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, cool
e...
War
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win
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, war
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Coole
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, war
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..
Coole
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cool
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7%0%
88%
5%
1. Warmer winters, cooler summers
2. Warmer winters, warmer summers
3. Cooler winters, warmer summers
4. Cooler winter, cooler summer
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B: How would glaciers change?
Glaci
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would g
row
Glaci
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would d
ecay
Glaci
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would s
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10%2%
88%1. Glaciers would grow
2. Glaciers would decay
3. Glaciers would stay about constant