1

Radiative Forcing

The balance between incoming solar radiation and

heat radiation leaving the atmosphere.

2

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.

3

Major Types of Radiative Forcings

Changes in …

Greenhouse Gases

Aerosols (particles)

Surface albedo

Contrails

Solar variability

Volcanic activity

4

Our Variable Star

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

5

Radiative Forcing: Balanced State

Radiative Balance

Radiative-Dynamic Balance

6

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

7

Carbon Dioxide (CO2)Pre-

industrial: ~ 280 ppm

Sources:1. Fossil fuels2. Cement

production3. Deforestation4. Biomass

burning

8

CO2 Emissions

13C/12C: Atmosphere >

Terrestrial Sources

O2 as CO2 : Combustion Plant respiration/photosy

nthesis

9

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?

10

Nitrous Oxide (N2O)

Sources:Coastal areas:continental shelves estuaries riversLand processes

11

Halocarbons

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

12

Other Gases

Stratospheric Ozone Tropospheric Ozone Stratospheric Water Vapor

13

Aerosol Effects

14

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

17

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

18

Solar Heating: Change

Variability due to 1. Changes in sunspots and

faculae2. Changes in solar diameter?

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Reconstructed Solar Heating

20

Volcanic Aerosols

21

Time Evolution of Forcing (Representative GCM)

Net RF: 1750 to 2005

23

Changes in Radiative Forcing