Climate Engineering with Stratospheric Aerosols and Associated Engineering Parameters. Ben Kravitz

Transcription

1 Climate Engineering with Stratospheric Aerosols and Associated Engineering Parameters Ben Kravitz

2 Colleagues Jason Blackstock Ken Caldeira Chris Fletcher David Keith Jane Long Doug MacMartin Alan Robock Everyone involved with GeoMIP

3 Why Stratospheric Aerosols? GISTEMP Tropospheric aerosols mask warming (global dimming) Recovery from volcanic eruptions dominates

4 Robock et al., 2008 Summer Monsoon Precipitation

5 Reasons geoengineering may be a bad idea (Slide courtesy of Alan Robock) Climate system response 1. Regional climate change, including temperature and precipitation 2. Rapid warming when it stops 3. How rapidly could effects be stopped? 4. Continued ocean acidification 5. Ozone depletion (Tilmes et al., 2008) 6. Enhanced acid precipitation (Kravitz et al., 2009) 7. Whitening of the sky (but nice sunsets) (Kravitz et al., 2012) 8. Less solar radiation for solar power, especially for those requiring direct radiation (Murphy, 2009) 9. Effects on plants of changing the amount of solar radiation and partitioning between direct and diffuse (Mercado et al., 2010) 10. Effects on cirrus clouds as aerosols fall into the troposphere 11. Environmental impacts of aerosol injection, including producing and delivering aerosols (Robock et al., 2009; McClellan et al., 2010) Robock, Alan, 2008: 20 reasons why geoengineering may be a bad idea. Bull. Atomic Scientists, 64, No. 2, 14-18, 59, doi: / Alan Robock Department of Environmental Sciences

6 Geoengineering Model Intercomparison Project GeoMIP Experiments G1-G4 for SRM with Stratospheric Aerosols G1 4 x CO 2 increase G2 Radiative Forcing Control run net forcing Radiative Forcing Control run net forcing solar constant reduction Time (yr) 0 50 Time (yr) G3 G4 Radiative Forcing net forcing Radiative Forcing SO 2 injection Time (yr) Time (yr) Kravitz et al., 2011

7 Geoengineering could reduce impacts of climate change on... Agriculture Water resources Weather extremes Sea level Biodiversity (and more)

8 Potential Climate Impacts of Geoengineering Potential Goals of Geoengineering (next few slides) Agriculture Water resources Weather extremes Sea level Biodiversity

9 scattering transmission absorption

10 Some tunable aerosol parameters Altitude Aerosol composition Aerosol size distribution Time of Year

11 less spatial control of radiative impacts Altitude space mesosphere longer atmospheric lifetime stratosphere ozone depletion? cirrus clouds? water vapor? chemistry? more spatial control of radiative impacts troposphere health impacts? acid rain? shorter atmospheric lifetime

12 Composition Sulfate Black Carbon scatters very well (mostly forward) surface chemistry acid deposition coagulation cloud nuclei highly absorbing surface chemistry (unknown!) health effects warming as it settles circulation changes Designer 1.0

13 Kravitz et al., 2012 Stratospheric Heating from Black Carbon

14 Kravitz et al., 2012 Ozone Loss?

15 Keith, 2010, PNAS

16 Size Distribution Cooling vs. warming effect Fall speed Surface area for chemical reactions Coagulation

17 Pierce et al., 2010, GRL

18 Time of Year 90 N Insolation (W m 2 ) N N Latitude S S S Mar 1 Jun 1 Sep 1 Dec 1 Time of Year 0 MacMartin et al., submitted

19 Shortwave radiative forcing at the surface (Northern Hemisphere average) for 5 Tg SO2 volcanic eruptions at different times of year December 1 March 1 June 12 August 8 W m-2 Kravitz and Robock, 2011

20 Feasibility Putting 1 Tg of stuff in the stratosphere would likely be cheap (a few billion dollars per year) IF it could be done in a way that achieves the desired effects

21 Parameters Climate Impacts Values altitude aerosol size composition surface cooling stratospheric warming ozone circulation cirrus clouds surface chemistry deposition effects health effects global vs. local effects... Agriculture Water resources Weather extremes Sea level Biodiversity

22 Conclusions ere are large uncertainties in the climate impacts of geoengineering. ere will always be uncertainties in the climate impacts of geoengineering. Decisions about geoengineering goals depend on both science and values. We are entering territory where there aren t comfortable answers. Under what conditions will geoengineering be used?

23 anks!