I. I.Climate Change – Greenhouse Gases A. A.Background Greenhouse Effect Gases absorb heat Natural...

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I. Climate Change – Greenhouse Gases A. Background Greenhouse Effect Gases absorb heat Natural Greenhouse Effect Mean planetary temperature = 15 o C vs. -6 o C Enhanced Greenhouse Effect Due to GHGs emitted from human activity B. Greenhouse Gases Most important GHG is water vapor Accounts for ~50% of natural GHE

Transcript of I. I.Climate Change – Greenhouse Gases A. A.Background Greenhouse Effect Gases absorb heat Natural...

Page 1: I. I.Climate Change – Greenhouse Gases A. A.Background Greenhouse Effect Gases absorb heat Natural Greenhouse Effect Mean planetary temperature = 15 o.

I. Climate Change – Greenhouse Gases

A. Background• Greenhouse Effect

• Gases absorb heat• Natural Greenhouse Effect

• Mean planetary temperature = 15 oC vs. -6 oC• Enhanced Greenhouse Effect

• Due to GHGs emitted from human activity

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

Influence

Carbon Carbon DioxideDioxide

FF CombustionFF Combustion

DeforestationDeforestation

Biomass BurningBiomass Burning

50-20050-200 11 55%55%

MethaneMethane Rice PaddiesRice Paddies

Cattle/TermitesCattle/Termites

LandfillsLandfills

FF ProductionFF Production

1010 2121 15%15%

Nitrous Nitrous OxideOxide

FertilizersFertilizers

DeforestationDeforestation

Biomass BurningBiomass Burning

150-170150-170 206206 6%6%

Halo-Halo-carbonscarbons

Aerosol SpraysAerosol Sprays

FoamsFoams

RefrigerantsRefrigerants

15-65015-650 10,700 – 10,700 – 15,80015,800

24%24%

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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• Important factor in cool period from 1930s to 1960s

• Overwhelmed effects of rising CO2 during this period

• Produced by volcanic eruptions, dust from areas experiencing drought

• Cool period following eruption of Mt. Pinatubo in 1992

• Mechanism behind “Nuclear Winter” scenario

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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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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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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. Wind Patterns• Affect atmospheric circulation and heat flux• Affect circulation of oceans and lakes

• 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

I. Astronomical Factors• 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

• Correlated with glacial periods over past 750,000 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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IPCC AR4