The climate cooling potential of different geoengineering options - PowerPoint PPT Presentation

The climate cooling potential of different geoengineering options Tim Lenton & Naomi Vaughan G eo E ngineering A ssessment & R esearch ( GEAR ) initiative School of Environmental Sciences, University of East Anglia, Norwich, UK www.gear.uea.ac.uk G eo E ngineering A ssessment & R esearch

Overview Climate context Method Cooling potential Side effects Conclusion G eo E ngineering A ssessment & R esearch

Prevention versus medicine Mitigation - Reducing greenhouse gas (especially CO 2 ) emissions Geoengineering “…large scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry.” National Academy of Sciences (1992) 1. Solar radiation management 2. Carbon dioxide removal G eo E ngineering A ssessment & R esearch

Future projections IPCC (2007) = High growth = Mid growth = Low growth G eo E ngineering A ssessment & R esearch

Potential climate tipping points Lenton et al. (2008) PNAS 105(6): 1786-1793 G eo E ngineering A ssessment & R esearch

Some tipping points may be too close Lenton and Schellnhuber (2007) Nature Reports Climate Change G eo E ngineering A ssessment & R esearch

Geoengineering options G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Geoengineering options Reflect more sunlight back to space Remove CO 2 from atmosphere and store it G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

How to quantify and compare them? Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561 Use radiative forcing (RF in W m -2 ) Linearly related to surface temperature change  T s =  RF Uncertain climate sensitivity parameter  = 0.6 – 1.2 K W -1 m 2 (best guess  = 0.86) Useful reference points: Current anthropogenic RF ~ 1.6 W m -2 Doubling CO 2 gives RF = 3.71 W m -2 G eo E ngineering A ssessment & R esearch

Solar radiation management Sunshades Reflect more sunlight back to space Stratospheric aerosols Increase cloud albedo Increase surface albedo G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Quantification Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561 Radiative forcing at top of atmosphere Depends on change in planetary albedo Change in planetary albedo depends on: Albedo change of layer affected Fraction of Earth’s area affected Prior absorption/reflection Changes in subsequent absorption/reflection Use global mean energy balance (land or ocean) G eo E ngineering A ssessment & R esearch

Reduce sunlight reaching the surface Sunshades Sunshades Stratospheric aerosols Cloud albedo Stratospheric aerosols - CCN biological, mechanical Increase cloud albedo G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Sunshades in space At L1 point (Angel 2006) 4.7 million km 2 Multiple ‘flyers’ ~0.3m 2 800,000 flyers/launch Just to counteract CO 2 rise of 2 ppm yr -1 requires: 35,700 km 2 yr -1 Cartoon of reflectors in space ~150,000 launches yr -1 RF = -3.71 W m -2 In principle but not in practice G eo E ngineering A ssessment & R esearch

Stratospheric aerosol injection Depends on aerosol type, amount, effective radius Inject into lower stratosphere over tropics 1.5–5 Mt S yr -1 to offset doubling CO 2 c.f. current ~50 Mt S yr -1 Stratospheric aerosols injection added to troposphere Mt Pinatubo eruption 1991 RF = -3.71 W m -2 Feasible G eo E ngineering A ssessment & R esearch

Enhancing cloud albedo Cloud albedo depends on density of cloud droplets Enhance this by adding condensation nuclei Sea salt, dimethyl sulphide Mechanically enhance cloud albedo Sensitivity depends on: – Stephen Salter Hygroscopicity of aerosol RF = -3.71 W m -2 Optical depth of cloud Feasible but uneven Changes in entrainment… G eo E ngineering A ssessment & R esearch

Increase reflection at the surface Cropland, Grassland Urban, human settlement Desert Increase surface albedo G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Increase surface albedo Desert Reflective cover over Cropland, grassland Variegated species, light shrubs, leaf waxes Human settlement, urban areas Reflective roof surfaces Paved surfaces, roofs… – Californian legislation Urban heat island Urban RF = -0.047 W m -2 50% global population G eo E ngineering A ssessment & R esearch

CO 2 removal from the atmosphere Remove CO 2 from atmosphere and store it Afforestation & Air reforestation capture Enhance Nutrient Carbonate downwelling Biochar addition addition Bio-energy capture Enhance upwelling G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Quantification Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561 Radiative forcing a logarithmic function of CO 2 RF = 5.35 ln(CO 2 /CO 2 ref ) Must specify reference concentration; CO 2 ref Any perturbation to atmospheric CO 2 decays away over time due to exchange with the ocean and land f(t) = 0.18 + 0.14 e –t/420 + 0.18 e –t/70 + 0.24 e –t/21 + 0.26 e –t/3.4 Removal flux of CO 2 is itself a function of time Must specify timescale of interest, chose 2050 and 2100 G eo E ngineering A ssessment & R esearch

Removal of CO 2 - Land BioEnergy Capture & Storage Air capture - ‘Artificial trees’ Biochar Afforestation Afforestation & Air reforestation capture Enhance Nutrient Carbonate downwelling Biochar addition addition Bio-energy capture Enhance upwelling G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Air capture and storage of CO 2 Chemical air capture More costly Biomass energy with carbon capture & storage (BECS) Maximum estimate Biofuels replace oil in transport Biomass replaces coal for electricity production Direct air capture 11.8 PgC yr -1 in 2100 – Klaus Lackner’s ‘artificial trees’ 771 PgC stored by 2100 RF (2050) = -0.74 W m -2 RF (2100) = -2.5 W m -2 G eo E ngineering A ssessment & R esearch

Biochar CO 2 removal Pyrolysis converts up to 50% of carbon in biomass to charcoal Maximum estimate 0.56 PgC yr -1 at present Scaling up using biomass energy production 3.15 PgC yr -1 in 2100 Total biochar reservoir Biochar – biomass burnt in near 148 PgC by 2100 zero oxygen (pyrolysis) Long term storage potential: RF (2050) = -0.12 W m -2 224 PgC global cropland RF (2100) = -0.40 W m -2 175 PgC temperate grassland G eo E ngineering A ssessment & R esearch

Removal of CO 2 - Ocean Addition of Iron, Nitrate, Phosphorus Ocean pipes Add carbonate Increase downwelling Afforestation & Air reforestation capture Enhance Nutrient Carbonate downwelling Biochar addition addition Bio-energy capture Enhance upwelling G eo E ngineering A ssessment & R esearch Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Ocean fertilisation Macronutrient addition Nitrate, Phosphate Micronutrient addition Iron fertilisation 12 Fe-addition patch experiments to date Assume removal of iron Iron addition to Fe-limited surface limitation globally waters to stimulate productivity Consider increase of sinking Iron Fertilisation organic carbon flux below RF (2050) = -0.11 W m -2 the depth of winter mixing RF (2100) = -0.20 W m -2 G eo E ngineering A ssessment & R esearch

Radiative forcing potential (in 2100) All blue values are in W m -2 >-3.1 All green values are in ppm of CO 2 >-3.1 -2.1 desert -0.51 grassland -0.35 cropland ~-3.1 500 ppm -0.15 settlements -0.05 urban areas +3.1 W m -2 ~-3.1 -34 -186 -0.2 -2 -37 -14 -19 -0.3 -0.37 -0.40 -2.5 -0.002 -0.20 -0.025 G eo E ngineering A ssessment & R esearch -0.15 -0.003 Lenton & Vaughan (2009) Atmospheric Chemistry and Physics 9: 5539-5561

Radiative forcing potential G eo E ngineering A ssessment & R esearch

Radiative forcing potential 1.6 3.7 G eo E ngineering A ssessment & R esearch

Side effects of reflecting sunlight Weakens the water cycle Promotes drought in monsoon regions e.g. India Commitment to long-term maintenance Sudden stop of activity causes rapid warming Ocean acidification Does not address this impact (may increase it) Regional climate changes Residual differences in global climate G eo E ngineering A ssessment & R esearch

Side effects of CO 2 removal Land Possible conflicts with other land uses Other greenhouse gases and albedo effects Ocean Ecosystem impacts Difficult verification and monitoring G eo E ngineering A ssessment & R esearch

Conclusion Climate change is a problem of risk management Already a risk of dangerous climate change even with strong mitigation Need to weigh up the risks of using or not using geoengineering 2 types of geoengineering with very different side effects and risks Sunlight reflection options could be reserved for use in emergency Carbon dioxide removal could complement mitigation efforts It is the only way to return to the pre-industrial atmospheric CO 2 level G eo E ngineering A ssessment & R esearch