"Future climate impacts of direct radiative forcing of anthropogenic aerosols, tropospheric ozone,

and long-lived greenhouse gases"

Chen, W; Liao, H; Seinfeld, J.H.

Journal of Geophysical ResearchPublished 26-July-2007

Presented by Jason EnglishJournal Club

26-September-2007

GHG and Trop. Ozone effect on climate

Climate Effects

Aerosol Effect on climate

Direct effectIndirect effect

Acid Rain (sulfates) Reduced VisibilityHealth Effects

Why are sulfate aerosols important?

Cause of Global Circulations

• Primary cause - uneven heating of the earth causes thermal wind, ocean-atmosphere coupling, Coriolis

• Can aerosols affect regional climate? If they affect global circulation, they might

Global aerosol RF: -0.5 W/m2

Asia aerosol RF: -10 to -50 W/m2

(includes natural)

Everything increases except sulfate, CFCs

A2 scenario: heterog. world, no sustainability, slow technology development - highest year 2100 CO2 and SO2 of all SRES scenarious

2 separate simulations with present climate use, 5 year integ. avg

•c

SO4

NO3

POA

•c

SOA

BC

O3

2000-2100 simulations

• Equilibrium climate used – GISS GCM, 4x5 resolution, 9 vertical layers, 1 hr time step– 80 yr integration; 50 yr spinup, 30 yr comparisons– This involves constant emissions and forcing– More pronounced differences than transient climate

• Aerosol RF– Internal mixtures– Refractive Indices parameterized from volume-weighted

mixing rule– Dry nitrate assumed same refractive index as dry sulfate– Gamma distribution SA-weighted dry r=0.3 um, variance=0.2– Mie theory applied to calculate extinction, SSA, g from

refractive indices and size distribution

•Overall, more energy into the system (TOA), but less directly to the surface

Change in RF 2000 - 2100

BC over snow,ice

Heating through most of the tropopause above the surface

Change in RF 2000 - 2100

Hot hot hot

Change in Surface T 2000 - 2100

BC over snow,ice

Scat.aerosols

Summer,fewerscat. aer.

High latitude GHG warmer due to ice-albedo feedbackHemispheric winter = more emissions

Change in Surface T 2000 - 2100

Change in Atmospheric T 2000 - 2100

Latent heat

•Aerosols weaken hadley cell DJF, strengthen it JJA

•GHG weakens hadley cell

Change in Streamfunction 2000 - 2100

baseline

Absolute humidity

relative humidity

AER & GHG cause increased evap in tropical lower trop = higher absolute humidity

Relative humidity controlled by Clausius Clapyron eqn

Excess precip change

convective precip change

AER hadley cell effect causes precip changes

GHG cause more heating = stronger convection

TOA SW flux

TOA LW flux

TOA SW flux affected by albedo and cloud cover changes

TOA LW flux affected by water vapor, clouds (GHG affects these)

Sea ice melting

More clouds

Surface SW flux

Surface latent heat

AER causes warmer air/cooler surface

GHG cause warmer air and surface

Surface sensible heat

•Why Asia? -> huge AER forcing

Regional WINTER Climate Change 2000 - 2100

•Aerosol composition change causes warming, Ozone causes warming, GHG cause warming….

Hot Hot Hot!