Royal Society - David Keith

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22 I September 2009 I Geoengineering the Climate The Royal Society
3 Solar radiation management techniques 3.1 Introduction The second major class of climate geoengineering methods aims to offset greenhouse warming by reducing the incidence and absorption of incoming solar (short-wave) radiation (often referred to as insolation). Solar radiation management (SRM) methods propose to do this by making the Earth more reflective, that is by increasing the planetary albedo, or by otherwise diverting incoming solar radiation. This provides a cooling affect to counteract the warming influence of increasing greenhouse gases. Various techniques have been proposed to produce this effect; these involve brightening the Earth’s surface, or introducing reflective matter into the atmosphere, or inserting lightscattering material in space between the Sun and the Earth. The concept is illustrated in Figure 3.1, which indicates how the solar radiation streams would respond. 3.2 General characteristics of SRM methods The aim of SRM methods is to produce a reduced (possibly near zero) net radiative forcing by balancing the positive forcing of greenhouse gases with a negative forcing introduced by reducing absorbed solar radiation. To balance the global mean radiative forcing of about + 4 W/m 2 that would arise from a doubling of CO 2 concentration (IPCC 2007a), the method would therefore need to provide a similar reduction in absorbed solar radiation. As can be seen from Figure 1.1, a method that resulted in an extra 1% of solar irradiance being reflected away from Earth would produce a radiative forcing of -2.35 W/m 2 . To balance a positive forcing of 4 W/m 2 therefore requires a reduction of about 1.8%. However, the impact on radiative forcing of a given SRM method is dependent on altitude, that is whether the method is applied at the surface, in the atmosphere, or in space, and on the radiative properties of the atmosphere and surface, as well as on its geographical location. Space-based SRM methods would require a diversion of about 1.8% of the incoming solar radiation. To have an equivalent radiative forcing effect, atmosphere or surfacebased methods would need to increase the planetary Figure 3.1. Schematic showing the impact of different SRM methods on solar radiation fluxes. Solar radiation reflected to space increased by atmosphere-based solar radiation management Solar radiation absorbed by atmosphere increased by surface-based solar radiation management Solar radiation reflected to space increased by cloud albedo solar radiation management Incoming solar irradiance reduced by space-based solar radiation management Solar radiation absorbed by atmosphere may be reduced or increased by stratosphere-based solar radiation management Solar radiation reflected to space increased by surface-based solar radiation management Solar radiation absorbed at surface reduced by all SRM methods The Royal Society Geoengineering the Climate I September 2009 I 23
Page 1 and 2: Geoengineering the climate Science,
Page 3 and 4: Geoengineering the climate: science
Page 5 and 6: Geoengineering the climate: science
Page 7 and 8: Foreword Lord Rees of Ludlow OM Pre
Page 9 and 10: Membership of working group The mem
Page 11 and 12: Summary Background Climate change i
Page 13 and 14: climate and environmental effects a
Page 15 and 16: 1 Introduction 1.1 Background Geoen
Page 17 and 18: Of this, more than 30% is reflected
Page 19 and 20: Box 1.2 Assessment of geoengineerin
Page 21 and 22: are provided for each method in Cha
Page 23 and 24: 2 Carbon dioxide removal techniques
Page 25 and 26: Table 2.2. Land-use and afforestati
Page 27 and 28: Table 2.4. Biochar summary evaluati
Page 29 and 30: Table 2.5. Summary evaluation table
Page 31 and 32: the carbon, converting it back into
Page 33 and 34: It might be argued that one easy wa
Page 35: e distributed effectively to avoid
Page 39 and 40: ightening, and the required change
Page 41 and 42: 3.3.2 Cloud-albedo enhancement It h
Page 43 and 44: eplacement vessels per year along w
Page 45 and 46: from Caldeira & Wood (2008) who hav
Page 47 and 48: These model experiments (also discu
Page 49 and 50: Table 3.6. Comparison of SRM techni
Page 51 and 52: 4 Governance 4.1 Introduction Clima
Page 53 and 54: ocean fertilisation, there may be a
Page 55 and 56: application, modification and exten
Page 57 and 58: • activities (and/or substances)
Page 59 and 60: Submission: Evans; Submission: IOP)
Page 61 and 62: 5 Discussion 5.1 Geoengineering met
Page 63 and 64: Figure 5.1. Preliminary overall eva
Page 65 and 66: egulated are needed. Public attitud
Page 67 and 68: Box 5.1 Research priorities 1. Cros
Page 69 and 70: The two major classes of geoenginee
Page 71 and 72: 6 Conclusions and recommendations D
Page 73 and 74: However SRM methods may provide a p
Page 75 and 76: 6.3 The UNFCCC should establish a w
Page 77 and 78: 7 References Aines R & Fiedmann J (
Page 79 and 80: Ding Y, Griggs DJ, Nouger M, van de
Page 81 and 82: Observations Compared to Projection
Page 83 and 84: 8 Annexes 8.1 Evaluation criteria P
Page 85 and 86: 8.3 Ethics panel The Royal Society
Page 87 and 88:
Dr Dan Lunt and Professor Paul Vald
Page 89 and 90:
9 Glossary AOGCMs Acid rain Aerosol
Page 91 and 92:
DECC Defra Deontological Detritus D
Page 93 and 94:
Peatlands Petagram Ppm Typically a
Page 95 and 96:
10 Acknowledgements We would like t
Page 97 and 98:
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