Transcript Sep 25 - University of San Diego

Climate Change – Greenhouse Gases
I.
A.
Background
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Greenhouse Effect
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B.
Gases absorb heat
Natural Greenhouse Effect
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Mean planetary temperature = 15 oC vs. -6 oC
Enhanced Greenhouse Effect
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Due to GHGs emitted from human activity
Greenhouse Gases
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Most important GHG is water vapor
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Accounts for ~50% of natural GHE
Greenhouse Gases
Gas
Carbon
Dioxide
Methane
Nitrous
Oxide
Halocarbons
Sources
Residence Radiative Influence
Time (y)
Forcing
FF Combustion
Deforestation
Biomass Burning
50-200
1
55%
Rice Paddies
Cattle/Termites
Landfills
FF Production
10
21
15%
Fertilizers
Deforestation
Biomass Burning
150-170
206
6%
Aerosol Sprays
Foams
Refrigerants
15-650
10,700 –
15,800
24%
http://calspace.ucsd.edu/virtualmuseum/climatechange2/07_2.shtml
Climate Change – Greenhouse Gases
I.
B.
Greenhouse Gases
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Long residence times indicate atmospheric
concentrations will remain high even if
emissions stop
Other factors besides GHGs may influence
global climate
Climate Change – Other Factors
II.
A.
Cloud Cover
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B.
Reflects incoming radiation
Difficult to estimate in climate models
Effects vary in relation to altitude, thickness,
composition
Atmospheric Dust
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Important factor in cool period from 1930s to 1960s
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Produced by volcanic eruptions, dust from areas
experiencing drought
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Overwhelmed effects of rising CO2 during this period
Cool period following eruption of Mt. Pinatubo in 1992
Mechanism behind “Nuclear Winter” scenario
Climate Change – Other Factors
II.
C.
Sunspots
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May affect amount of incoming radiation
Solar output varies – sunspots, solar flares
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Sunspots are magnetic storms that appear as dark
patches on sun’s surface
Number and size are maximal every 11 years
Solar output ca. 0.1% higher than normal during
maxima
http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml
Climate Change – Other Factors
II.
C.
Sunspots
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May affect amount of incoming radiation
Solar output varies – sunspots, solar flares
Researchers have correlated minima with
“Little Ice Age” in Europe during 17th and
early 18th centuries when sun was 0.25%
dimmer than normal
20th century dominated by sunspot maxima
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Some predictions that 21st century will see minima
Estimated that sunspot variability may have
contributed to half of 0.55 oC warming since
1860 and one third of warming since 1970
(Lean et al.)
http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml
Climate Change – Other Factors
II.
D.
Volcanism
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Affects water vapor, particles, sulfides, nitrates
Generally leads to planetary cooling
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E.
Theory about extinctions at P/T & K/T boundaries
Mt. St. Helens and Mt. Pinatubo eruptions caused
planetary cooling, and those were small eruptions
Photosynthesis & Transpiration
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Affect CO2, water vapor
As [CO2] rises, some plants
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Photosynthesize more rapidly
Grow faster
Incorporate more CO2 into biomass
Keep their stomata open less
Transpiration releases water vapor into atmosphere
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Less transpiration when [CO2] is higher (stomata)
Climate Change – Other Factors
II.
F.
Soil Characteristics
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Affect heat capacity and retention
More hydrated soil leads to
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G.
Darker color (less reflective)
More heat capacity (high heat capacity of water)
Albedo (Reflectivity)
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Earth’s surface varies considerably (mean = 0.30-0.36)
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Ice/Snow highly reflective (0.9)
Clouds vary in reflectivity
Land generally less reflective
Changes in land use affect albedo
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Desertification increases albedo
Forest – 0.12
Grassland – 0.19
Desert – 0.30
Climate Change – Other Factors
II.
H.
Wind Patterns
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Affect atmospheric circulation and heat flux
Affect circulation of oceans and lakes
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I.
Wind mixes warm water down and brings cooler,
nutrient-rich water to surface
May affect photosynthesis & removal of CO2 from
atmosphere
Ex – El Niño results from changes in wind patterns
Astronomical Factors
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Earth’s axis precesses on a 26,000 year cycle
Axial tilt varies on a 41,000 year cycle
Orbital eccentricity has a 100,000 year cycle
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Correlated with glacial periods over past 750,000 years
http://www.clearlight.com/~mhieb/WVFossils/ice_ages.html
Climate Change – Other Factors
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Many factors affect global climate in multiple
ways
Ex – Clouds absorb re-radiated longwavelength radiation but also may reflect
incoming short-wavelength radiation
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Ex – Particles in the atmosphere reduce the reradiation of long-wavelength radiation but also
reflect incoming short-wavelength radiation
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Net effect is cooling
Net effect is probably warming at low levels but
cooling at high levels (e.g. following a large volcanic
eruption)
Uncertainty about impact of many factors
IPCC AR4