Climate Change

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• Climate Change Greenhouse Gases
• Background
• Greenhouse Effect
• Gases absorb heat (not light)
• Natural Greenhouse Effect
• Mean planetary temperature 15 oC vs. -6 oC
• Enhanced Greenhouse Effect
• Due to GHGs emitted from human activity

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• Climate Change Greenhouse Gases
• Greenhouse Gases
• Most important GHG is water vapor
• Accounts for 50 of natural GHE

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Greenhouse Gases
Gas Sources Residence Time (y) Radiative Forcing Relative Influence
Carbon Dioxide FF Combustion Deforestation Biomass Burning 50-200 1 63
Methane Rice Paddies Cattle/Termites Landfills FF Production 10 21 18
Nitrous Oxide Fertilizers Deforestation Biomass Burning 150-170 206 6
HCs (incl. CFCs) Aerosol Sprays Foams Refrigerants 15-650 10,700 15,800 13
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After Petit et al. 1999
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• Climate Change Greenhouse Gases
• Greenhouse Gases
• Long residence times indicate atmospheric
  concentrations will remain high even if emissions
  stop
• Other factors besides GHGs may influence global
  climate

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• Climate Change Other Factors
• Cloud Cover
• Reflects incoming radiation
• Difficult to estimate in climate models
• Effects vary in relation to altitude, thickness,
  composition
• Atmospheric Dust Aerosols
• Important factor in cool period from 1930s to
  1960s
• Overwhelmed effects of rising CO2 during this
  period
• Dust from volcanic eruptions, drought areas
• Cool period following eruption of Mt. Pinatubo in
  1991
• Anthropogenic aerosols from sulfate, nitrate,
  black carbon, etc. (mostly from combustion)
• Also may influence cloud lifetime, precipitation

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• Climate Change Other Factors
• Sunspots
• May affect amount of incoming radiation
• Solar output varies sunspots, solar flares
• Sunspots are magnetic storms that appear as dark
  patches on suns surface
• Number and size are maximal every 11 years
• Solar output ca. 0.1 higher than normal during
  maxima

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http//calspace.ucsd.edu/virtualmuseum/climatechan
ge2/06_3.shtml
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• Climate Change Other Factors
• Sunspots
• 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
• 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.)

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http//calspace.ucsd.edu/virtualmuseum/climatechan
ge2/06_3.shtml
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• Climate Change Other Factors
• Volcanism
• Affects water vapor, particles, sulfides,
  nitrates
• Generally leads to planetary cooling
• 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
• Affect CO2, water vapor
• As CO2 rises, some plants
• Photosynthesize more rapidly
• Grow faster
• Incorporate more CO2 into biomass
• Keep their stomata open less
• Transpiration releases water vapor into
  atmosphere
• Less transpiration when CO2 is higher (stomata)

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• Climate Change Other Factors
• Volcanism
• Affects water vapor, particles, sulfides,
  nitrates
• Generally leads to planetary cooling
• 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
• Affect CO2, water vapor
• As CO2 rises, some plants
• Photosynthesize more rapidly
• Grow faster
• Incorporate more CO2 into biomass
• Keep their stomata open less
• Transpiration releases water vapor into
  atmosphere
• Less transpiration when CO2 is higher (stomata)

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• Climate Change Other Factors
• Soil Characteristics
• Affect heat capacity and retention
• More hydrated soil leads to
• Darker color (less reflective)
• More heat capacity (high heat capacity of water)
• Albedo (Reflectivity)
• Earths surface varies considerably (mean
  0.30-0.36)
• Ice/Snow highly reflective (0.9)
• Clouds vary in reflectivity
• Land generally less reflective
• Changes in land use affect albedo
• Desertification increases albedo
• Forest 0.12
• Grassland 0.19
• Desert 0.30

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• Climate Change Other Factors
• Astronomical Factors
• Earths axis precesses on a 23,000 year cycle
• Axial tilt (obliquity) varies on a 41,000 year
  cycle
• Orbital eccentricity has a 100,000 year cycle
• Correlated with glacial periods over past
  1,000,000 years

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• Climate Change Other Factors
• Many factors affect global climate in multiple
  ways
• Ex Clouds absorb re-radiated long-wavelength
  radiation but also may reflect incoming
  short-wavelength radiation
• Net effect is cooling
• Ex Particles in the atmosphere reduce the
  re-radiation of long-wavelength radiation but
  also reflect incoming short-wavelength radiation
• 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

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