1 radiative forcing the balance between incoming solar radiation and heat radiation leaving the...

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Radiative Forcing

The balance between incoming solar radiation and

heat radiation leaving the atmosphere.

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Key Findings

1.Extremely likely (> 95%) that humans have exerted a substantial warming influence on climate since 1750.

2.Likely (> 66%) that the human influence by radiative forcing is at least 5 times greater than solar influence since 1750.

3.Exceptionally unlikely (> 99%) that solar + volcanic radiative forcing for 1950-2005 was comparable to anthropogenic radiative forcing.

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Major Types of Radiative Forcings

Changes in …

Greenhouse Gases

Aerosols (particles)

Surface albedo

Contrails

Solar variability

Volcanic activity

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Our Variable Star

Changes of ~ 0.2% (= 2.7 W m-2) reflect 11-year sunspot cycle

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Radiative Forcing: Balanced State

Radiative Balance

Radiative-Dynamic Balance

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Radiative Forcing

Change in net radiative energy flux at the tropopause with …

(a) stratospheric temperatures readjusted to radiative equilibrium

(b) surface and tropospheric temperatures and state held fixed at original values

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Carbon Dioxide (CO2)Pre-

industrial: ~ 280 ppm

Sources:1. Fossil fuels2. Cement

production3. Deforestation4. Biomass

burning

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CO2 Emissions

13C/12C: Atmosphere >

Terrestrial Sources

O2 as CO2 : Combustion Plant respiration/photosy

nthesis

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Methane (CH4)

NOAA Global Monitoring Division (GMD)

Advanced Global Atmospheric Gases Experiments (AGAGE)

Sources:Biogenic:WetlandsRiceBiomass burningRuminantsFossil fuel mining & distribution Living vegetation?

Mt. Pinatubo?

Economic Incentives?

Warm 1998?

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Nitrous Oxide (N2O)

Sources:Coastal areas:continental shelves estuaries riversLand processes

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Halocarbons

Small amounts, but effective absorbers of infrared radiationFactors:Industrial processesPartly regulated by Montreal Protocol

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Other Gases

Stratospheric Ozone Tropospheric Ozone Stratospheric Water Vapor

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Aerosol Effects

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Aerosol Types

Sulphate Organic Carbon from Fossil Fuels Black Carbon from Fossil Fuels Biomass Burning Nitrate Mineral Dust

Aerosol Distributions

Biomass Burning

Optical Depth: Radiative Thickness”

Mineral Dust

Industrial

Sea Salt

White: measurement not possible

Land Use Changes

Albedo DifferencesForest < CroplandSnow-covered forest < Snow-covered cropland

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Other Surface Effects

Black Carbon on Snow/Ice Land-Use Changes on Surface Fluxes Anthropogenic Water Vapor Release Anthropogenic Energy Release CO2 Influence on Plant Physiology

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Solar Heating: Change

Variability due to 1. Changes in sunspots and

faculae2. Changes in solar diameter?

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Reconstructed Solar Heating

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Volcanic Aerosols

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Time Evolution of Forcing (Representative GCM)

Net RF: 1750 to 2005

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Changes in Radiative Forcing