climate change – greenhouse gases background greenhouse effect gases absorb heat (not light)
DESCRIPTION
Climate Change – Greenhouse Gases Background Greenhouse Effect Gases absorb heat (not light) Natural Greenhouse Effect Mean planetary temperature = 15 o C vs. -6 o C Enhanced Greenhouse Effect Due to GHGs emitted from human activity. Climate Change – Greenhouse Gases Greenhouse Gases - PowerPoint PPT PresentationTRANSCRIPT
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I. Climate Change – Greenhouse Gases
A. 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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I. Climate Change – Greenhouse Gases
B. Greenhouse Gases• Most important GHG is water vapor
• Accounts for ~50% of natural GHE
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Greenhouse GasesGas Sources Residence
Time (y)Radiative Forcing
Relative
Influence
Carbon Carbon DioxideDioxide
FF CombustionFF Combustion
DeforestationDeforestation
Biomass BurningBiomass Burning
50-20050-200 11 63%63%
MethaneMethane Rice PaddiesRice Paddies
Cattle/TermitesCattle/Termites
LandfillsLandfills
FF ProductionFF Production
1010 2121 18%18%
Nitrous Nitrous OxideOxide
FertilizersFertilizers
DeforestationDeforestation
Biomass BurningBiomass Burning
150-170150-170 206206 6%6%
HCsHCs(incl. CFCs)(incl. CFCs)
Aerosol SpraysAerosol Sprays
FoamsFoams
RefrigerantsRefrigerants
15-65015-650 10,700 – 10,700 – 15,80015,800+
13%13%
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After Petit et al. 1999
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I. Climate Change – Greenhouse Gases
B. 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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II. Climate Change – Other Factors
A. Cloud Cover• Reflects incoming radiation• Difficult to estimate in climate models• Effects vary in relation to altitude, thickness,
composition
B. 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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II. Climate Change – Other Factors
C. Sunspots• May affect amount of incoming radiation• Solar output varies – sunspots, solar flares
• 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
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http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml
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II. Climate Change – Other Factors
C. 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/climatechange2/06_3.shtml
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II. Climate Change – Other Factors
D. 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
E. 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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II. Climate Change – Other Factors
D. 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
E. 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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II. Climate Change – Other Factors
F. Soil Characteristics• Affect heat capacity and retention• More hydrated soil leads to
• Darker color (less reflective)• More heat capacity (high heat capacity of water)
G. Albedo (Reflectivity)• Earth’s 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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II. Climate Change – Other Factors
H. Astronomical Factors• Earth’s 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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II. 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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