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Aerosols and Climate

Aerosols and Climate. V. Ramaswamy (“Ram”) U.S. National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory Princeton University [USA]. Human and Natural Drivers of Climate Change. IPCC (2007). Lecture # 3.

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Aerosols and Climate

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  1. Aerosols and Climate V. Ramaswamy (“Ram”) U.S. National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory Princeton University [USA]

  2. Human and Natural Drivers of Climate Change IPCC (2007)

  3. Lecture # 3 • Diagnosing the role of aerosols in the 20th century climate change using models and observations. • Uncertainties associated with aerosols in past and future climate changes, including hints of nonlinearity, and “non-straightforward” climate impacts due to aerosol additions/ removals.

  4. What is a State-of-the-Art Global Climate Model? Unfortunately, we don’t have atwin planet earth that we can use to perform large-scale climatelaboratory experiments.

  5. What is a State-of-the-Art Global Climate Model? • The computer is our lab. • The computer model is our research tool.

  6. Anthro+ Nat forcing Attribution • Asks whether observed changes are consistent with • expected responses to forcings • inconsistent with alternative explanations Most of the observed increase in globally averaged temperatures since mid-20th century is very likely (>90% certainty) due to the observed increase in anthropogenic GHG concentrations TS-23 IPCC (2007)

  7. Radiative Forcing (All forcing agents) Radiative Forcing (BC+OC) Radiative Forcing (Anthro. Aerosol  BC,OC,Sulfate)

  8. If the 20th century had been “driven” by LLGHGs and Ozone only………… 2000 1860

  9. The 20th century climate “driven” by all known forcing agents 2000 1860

  10. Schwarzkopf and Ramaswamy (2008)

  11. Delworth et al. (2005)

  12. Delworth et al. (2005)

  13. Simulated North Atlantic AMOC Index Aerosol only forcing All forcings Greenhouse gas only forcing

  14. UncertaintiesDust aerosols’ roleSensitivity to aerosol microphysicsAerosol-Cloud interaction

  15. Global Dust - the last 50 Years ? Dust concentration at Barbados (Prospero and Lamb, 2003) Factor 4 increase Sahel drought Fuyu Li et al. (2008) {GFDL AM2n} Correlation at Barbados (Prospero and Lamb, 2003) Since 1970ies dust concentration in Caribbean (Prospero and Lamb, 2003) and dust deposition in French Alps (De Angelis and Gaudichet, 1991) have increased by a factor 4-5 Barbados Dust Sahel Precipitation Index (previous year)

  16. Aerosol vs. Dynamics Aerosol Indirect Effects (1st and 2nd) Clean/Maritime Polluted/Continental Ramanathan et al. (2001)

  17. A new paradigm  Treating the ‘direct’ and ‘indirect’ aerosol effect as a TOTAL AEROSOL EFFECT (TAE) How large?? Atmosphere + MIxed-Layer Ocean Equilibrium simulations to compare Greenhouse gas and Aerosol effects WMGG  well-mixed gases d  direct s  semi-direct i  total indirect Ming-Ramaswamy (JC, in press)

  18. Ming and Ramaswamy (J. Climate, in press)

  19. Differing roles of Scattering AND Absorbing AerosolsExperiments with the GFDL Atmospheric Model {a la “Menon-ic” investigations}:- prescribed SSTs- consider aerosol increases over India and China from the 1950 to 1990s (guided byavailable observations)- consider the uncertainty of the scattering and absorbing components

  20. Scattering and Absorbing Aerosol over Asia Jeff Schmaltz/Moderate Resolution Imaging Spectroradiometer Land Rapid Response Team NASA Goddard The SeaWiFS Project and GeoEye, Scientific Visualization Studio NASA Goddard Uncertainties remain regarding: 1. The amount of extinction due to increasing amounts of aerosols. 2. The amount of aerosol absorption. India China Estimated fossil-fuel black carbon emissions since 1875, in GT per year [Chen, Berkeley Lab Science Beat, July 14, 2004]. Changes  1950 to 1990s Sensitivity of climate to changes in aerosol extinction and absorption? Impacts on precipitation and circulation in the Asian region?

  21. Precipitation Rate Change (∆P [mm d-1]) ωo= 0.85 ωo= 0.99 XCa XChW -0.2 -0.2 -1.1 -0.6 Contour interval is 1 mm d-1. Change in JJA precipitation rate [mm d-1] between the BASE and experiments; change in aerosols is the only external forcing. Land-area average given in figure for India (green) and China (red). Low ωo High Absorption High ωo Low Absorption ωo = 0.85 ωo = 0.99

  22. Change in Surface Pressure ωo= 0.85 ωo= 0.99 XCa XChW Contour interval 0.4 hPa. Change in JJA surface pressure (∆Psfc) [hPa] between the BASE and experiments; change in aerosols is the only external forcing. Low ωo High Absorption High ωo Low Absorption ωo = 0.85 ωo = 0.99

  23. XCa ωo = 0.85 XChW ωo = 0.99 India Ocean Land Ocean Land XCa ωo = 0.85 XChW ωo = 0.99 China ωo = 0.85 ωo = 0.99 ωo = 0.85 ωo = 0.99 XCa XChW XCa XChW Ocean Land Ocean Land Cloud Amount & Vertical Velocity Change ΔCloud Amount [%] over Land Zonally averaged change in vertical velocity [hPa s-1× 10-5] relative to the BASE. Red is increased upward motion. Blue is relative subsidence. Contour interval 5 hPa s-1× 10-5. Low ωo High Absorption High ωo Low Absorption ωo = 0.85 ωo = 0.99

  24. Low w High w • Increases (decreases) in cloud amount can reduce (enhance) the surface solar flux reduction to the surface associated with high aerosol extinction optical depths and thus can increase (decrease) surface radiative cooling. • Increased (decreased) aerosol absorption optical depth can enhance (spin-down) the hydrological cycle over the Asian land-mass. • Summary table (right) shows sign change relative to BASE case over land areas. XCa XChW XCa XChW

  25. The FutureWhat will be the impacts of changes in Greenhouse Gases and Aerosols?

  26. Key Points: Most CO2 emission scenarios level off or decrease by 2100 Most sulfate emissions decrease by 2030

  27. A1B Warming (CM 2.1) 2020s ~2050 2070s 2090s

  28. Summer Surface Air Temperature Change A1B Scenario 2090s – 2000s AllForce GHGs only Aerosol Reduction effect Levy et al., (JGR, 2008)

  29. Human Socio-Economic Scales Clouds Aero- sols The “Great Spatial Scaling” problem in Climate and impacts

  30. Principal Sources • Atmospheric Radiation lectures [Boulder, 1986] • “Global Physical Climatology” by D. HARTMANN • Intergovernmental Panel on Climate Change, 2001 and 2007, Working Group I (The Physical Science Basis) • Ming and Ramaswamy (Journal of Climate, in press) • C. Randles Ph. D. thesis (Princeton University, 2007); JGR (2008, in press) • Fuyu Li’s Graduate Research (Princeton University); JGR (2008)

  31. The END Thank you for your attention !

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