Climate Change Greenhouse Gases - PowerPoint PPT Presentation

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Climate Change Greenhouse Gases

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Albedo (Reflectivity) Earth's surface varies considerably (mean = 0.30-0.36) ... Changes in land use affect albedo. Desertification increases albedo. Forest 0.12 ... – PowerPoint PPT presentation

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Title: Climate Change Greenhouse Gases


1
  • 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

4
Greenhouse Gases
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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

9
  • 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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11
  • 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

12
http//calspace.ucsd.edu/virtualmuseum/climatechan
ge2/06_3.shtml
13
  • 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.)

14
http//calspace.ucsd.edu/virtualmuseum/climatechan
ge2/06_3.shtml
15
  • 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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17
  • 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)

18
  • 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

19
  • 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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22
  • 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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