Stratospheric sulfate geoengineering has limited efficacy and increases tropospheric sulfate burdens

Transcription

1 Stratospheric sulfate geoengineering has limited efficacy and increases tropospheric sulfate burdens Jason English PhD Candidate Laboratory for Atmospheric and Space Physics, and Department of Atmospheric and Oceanic Sciences University of Colorado at Boulder June 21, 2011 Advisor: Brian Toon Collaborator: Michael Mills Funding: NASA, NSF

2 The stratospheric sulfate geoeng. approach Why the stratosphere? Aerosols stay aloft 100x longer Inject ~5 to 20 Tg SO 2 /yr Balloons, tall pipes, aircraft, artillery Cost: <$2 to 200 billion/yr This may be economical Drawing by Brian West. Robock et al., 2009

3 Mt. Pinatubo (1991) demonstrated cooling ~20 Tg SO 2 into stratosphere 1992: Temperature dropped 0.5 C; coolest year in the past 25 years We also saw ozone loss, hydrological changes

4 WACCM/CARMA Coupled Model 2. Chemistry 3. Nucleation Nuc: Zhao and Turco 1995 H 2 O vp: Lin & Tabazadeh 2001 H 2 SO 4 vp: Giauque/Ayers/Kulmala WACCM CARMA 4 x 5 resolution Dynamics/Transport WACCM CARMA 4. Growth H 2 SO 4 vp: Giauque/Ayers/Kulmala Wt %: Tabazadeh 1997 CARMA 5. Coagulation H 2 SO 4 formed Oxidants OH, O, O 3,NO 3 WACCM 1. Emissions CARMA 42 bins r dry = 0.2 nm-2.6 µm Brownian, convective, & gravitational effects Toon et. al WACCM CARMA 6. Deposition, Sedimentation SO 2 (UT source only) OCS (510 pptv boundary condition) Aerosol radiative effects not coupled, but het chem is 5 year simulations; 5 th year analyzed

5 Five SO 2 injection schemes (50 mb, 4N-4S, all longitudes)

6 Geoengineered effective radius is larger

7 Simulated Pinatubo R eff reaches peak sooner than obs; Simulated Geoeng R eff larger than Pinatubo Jan-91 Feb-91 Mar-91 Apr-91 May-91 Jun-91 Jul-91 Aug-91 Sep-91 Oct-91 Nov-91 Dec-91 Jan-92 Feb-92 Mar-92 Apr-92 May-92 Jun-92 Jul-92 Aug-92 Sep-92 Oct-92 Nov-92 Dec-92 Jan-93 Feb-93 Mar-93 Apr-93 May-93 Jun-93 Jul-93 Aug-93 Sep-93 Oct-93 Effective Radius (microns) 1.0 Pinatubo Obs (35-45 N, mb) 10 Tg Geoeng (30S-30N, mb) 0.9 Pinatubo Sim (35-45 N, mb) Pinatubo Sim (30S-30N, mb)

8 Larger particles fall faster and RF less effective Pinatubo Obs (35-45 N, mb) Pinatubo Sim (35-45 N, mb) 10 Tg Geoeng (30S-30N, mb) Pinatubo Sim (30S-30N, mb) Particle radius (microns) V fall (mm/s) Mass scattering efficiency (m 2 /g) Effective Radius (microns) Jan-91 Feb-91 Mar-91 Apr-91 May-91 Jun-91 Jul-91 Aug-91 Sep-91 Oct-91 Nov-91 Dec-91 Jan-92 Feb-92 Mar-92 Apr-92 May-92 Jun-92 Jul-92 Aug-92 Sep-92 Oct-92 Nov-92 Dec-92 Jan-93 Feb-93 Mar-93 Apr-93 May-93 Jun-93 Jul-93 Aug-93 Sep-93 Oct-93

9 Two microphysical studies compare well, and differ significantly from GCM-only simulations 10 Aerosol Burden (Tg S) Rasch et al. Heckendorn et al. This Work Stratospheric Sulfur Injection (Tg S/yr)

10 Continuous injection has lower AOD than a Volcano

11 1/3 of total burden is in the troposphere; 1/3 of that is in the first 100 hpa below the tropopause Aerosol Burden (Tg S) Rasch et al. Troposphere Heckendorn et al. First 100 hpa Whole Atmos hpa Stratosphere Second 100 hpa Stratospheric Sulfur Injection (Tg S/yr)

12 Continuous injection adds more burden to troposphere Trop Strat Trop Strat

13 Geoeng increases tropospheric burden in the upper troposphere and high latitudes up to 100x

14 Geoeng increases aerosol number, area, and volume in the upper troposphere

15 Our 3D microphysical simulations of stratospheric SO 2 injection suggest Geoengineered effective radius is larger than Pinatubo; shorter lifetime limits aerosol burden to ~6 Tg burden (~2 W m -2 ) Results compare favorably to Heckendorn et al. Geoeng increases tropospheric aerosol burden, especially high altitude and latitude Troposphere increases 5x; upper troposphere by 30x; high latitudes by 30x Could impact tropospheric clouds, radiative forcing, and chemistry Other consequences previously identified: Ozone destruction / stratospheric chemistry changes Acid deposition in mid/high latitudes Hydrological changes/reduced precipitation Stratospheric lifetime may be increased by Sulfur sources with slower conversion to aerosol Other aerosol types Higher injection / more spread out

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17 Why are sulfate aerosols so special? Sulfates have high extinction (ability to reflect and absorb radiation) Takemura et al Sulfates have high Single Scattering Albedo (they prefer to reflect radiation rather than absorb it) What does SO 2 have to do with sulfate aerosols?

18 And the particles that are there, aren t as effective at scattering radiation Pinatubo: 6 m 2 /g 13 Tg geoeng: 2 m 2 /g Particle diameter (microns) IPCC, 2001

19 The sulfate aerosol life cycle 1. emissions 2. chemistry 3. nucleation 4. growth 5. coagulation 6. deposition Mt. Pinatubo (20 Tg SO 2 ), geoengineering (? Tg SO 2 ) Sulfuric acid is made an aerosol is born evaporation, condensation particles collide and combine particles fall to the earth 0.1 nm H 2 O H 2 O 1 nm SO 2 H 2 SO 4 SO 2 (g) + OH (g) H 2 SO 4 (g) H 2 SO nm Most climate models parameterize some of these processes (esp. nucleation, growth, coagulation)