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Geoengineering Defined Geoengineering is the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change.

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Presentation on theme: "Geoengineering Defined Geoengineering is the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change."— Presentation transcript:


2 Geoengineering Defined Geoengineering is the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change

3 Why Geoengineering? CO2 already at 390 ppm and increasing Kyoto protocol targets stabilization at 450 ppm to limit temperature change of 2 C No evidence that nations will meet the emission reduction targets needed to stabilize at 450 ppm Emissions are actually increasing faster than projected Large uncertainty about tipping points (sudden thaw of the permafrost for example, very rapid loss of polar ice fields) Continued uncertainty in actual climate sensitivity Large time lag in climate system

4 Why not Geoengineering? Could reduce fragile political and public support for international mitigation efforts Divert resources from adaptation and mitigation Pose significant environmental risks—large unknowns Large uncertainties in actual effectiveness and feasibility Range of possible solutions—which one? Who pays? Ethical issue: Is it morally wrong to use an artifical solution in place of reducing emissions to address climate change There is no regulatory framework—who decides to implement a geoengineering method?

5 How do we evaluate geoengineering methods? Royal Society Study; Geoengineering the climate: science, governance and uncertainty, 2009 Evaluation criteria Effectiveness Timeliness Safety Cost Reversibility

6 Brief Review of Earth’s Energy Budget Which components could be modified to reduce solar heating? 1% change (2.35 W/m2) produces 1.8 C surface temperature change

7 The Global Carbon Cycle Which fluxes could be modified to decrease CO2 in the atmosphere Doubling of CO2 to 550 ppm equals radiative forcing of 4 W/m2 (3 C warming)

8 Two Primary Approaches Carbon dioxide removal (CDR) from the atmosphere Solar radiation management (SRM) to reduce net incoming solar energy

9 Carbon Dioxide Removal (CDR) Methods Enhance uptake and storage by the terrestrial biosphere Enhance uptake and storage by the marine biosphere Use engineered systems to sequester carbon

10 Solar Radiation Management Methods Surface based modification of albedo (reflectivity) of the land or ocean Troposphere based modification of albedo (cloud modification) Upper atmosphere based modification of reflectivity Space based engineered interception of incoming solar

11 Carbon Dioxide Removal(CDR) Biological Afforestation and land use Biomass/fuels with carbon sequestration Iron/nitrogen/phosphorus fertilization of the ocean Enhance upwelling of deep ocean waters Physical Atmospheric CO2 scrubbers Change in ocean overturning circulation Chemical (enhanced weathering) In-situ carbonation of silicates on land Basic minerals on soil Oceanic alkalinity enhancement

12 CDR Considerations Spatial scale Chemical and physical methods might require an industry as large as fossil fuel production Biological methods might require land at a scale similar to global agriculture Temporal scale Must approach or exceed 8.5 GtC/yr (Current emissions levels) Must be maintained for decades or centuries Must be implemented soon to be effective

13 Land-based CDR Increase afforestation and reforestation and decrease deforestation—at a scale much larger than currently exists 0.8 Gt/yr by 2030—offset 2% to 4% of C emissions

14 Biochar and biomass methods: Harness the growth of biomass to store C Land C sinks—long term sequestration of C in soils Bioenergy with Carbon Capture & Sequestration (not considered geoengineering) Biomass for sequestration—bury trees, crop wastes, or as charcoal biochar

15 Biochar Heat biomass in a low or no oxygen environment to produce charcoal and syngas and bio-oil C in biochar much more stable than in organic C forms Wide range of feedstocks—ag waste, woody residue, straw, etc Addition of biochar might improve agricultural soil productivity Better to bury biochar or just burn biomass/biochar as a biofuel for power and heat? Could require large land areas in competition with agricultural uses Lack of quantitative information and large uncertainties

16 Enhanced weathering (land and oceans) CaSiO3 + CO2 == CaCO3 + SiO2 0.1 GtC/yr currently due to natural weathering Accelerate weathering artificially on land Add silicates to agricultural soils (7 km3 per year—twice current coal mining rates) Impact on soil productivity is unknown Carbonate rocks used in chem engineering plants reacted with CO2 from power plants dispose of HCO3 solutions in the ocean increases ocean alkalinity-offsets CO2 acidity Slight increase in alkalinity could take up all excess CO2 in the atmosphere Large scale mining, transportation, processing will be required Costs, environmental impacts could be large


18 CO2 Capture from the Atmosphere Adsorption on solids (similar to current methods being tested for Carbon Capture & Sequestration) Adsorption into alkaline solutions (NaOH in high concentrations) Adsorption into alkaline solutions (moderate concentrations) with a microbial enzyme catalyst—factor of 100 more effective All methods require energy to move air through the adsorption system Resulting material must be transported and sequestered Costs could be competitive since plants can be located near the sequestration location or at ‘stranded’ energy sources


20 Oceanic Uptake of CO2 Biological Pump Algae photosynthesize CO2 in surface waters Algae and other bio remains sink and take C to deep ocean C is respired at deep levels as CO2 Effect is to pump CO2 from the surface to deep waters Biological pump is limited by nutrients needed by surface organisms Limiting nutrients include Nitrogen, Phosphorus and Iron (location varies) C:N:P:Fe ratios 106 : 16 : 1 : 0.001 (1 mole P could lock up 106 moles of C) Efficiency of adding nutrients to C stored is highly uncertain Perhaps 1GtC/yr could be sequestered



23 Carbon Dioxide Removal Summary All of the CDR methods have the dual benefit that they address the direct cause of climate change and also reduce direct consequences of high CO2 levels including surface ocean acidification (but note that the effect of ocean fertilisation is more complex). However, they have a slow effect on the climate system due to the long residence time of CO2 in the atmosphere and so do not present an option for rapid reduction of global temperatures. If applied at a large enough scale and for long enough, CDR methods could enable reductions of atmospheric CO2 concentrations (or negative emissions) and so provide a useful contribution to climate change mitigation efforts. Significant research is however required before any of these methods could be deployed at a commercial scale. In principle similar methods could also be developed for the removal of non-CO2 gases from the atmosphere.

24 Solar Radiation Management Need 1.8% (4W/m2) solar reduction to offset 2xCO2 More than 1.8% is needed for lower atmosphere surface SRM SRM should have an immediate effect SRM would have immediate termination impacts

25 Increase surface albedo (reflectivity) Average albedo is 0.15 Globally increase to 0.17, but oceans are most of the surface On land, not all area can be modified so increases to as much as 1.0 are needed White roof of the built environment—only 0.2 W/m2 Reflective crops and grasslands—1.0 W/m2 might be possible—could reduce ecosystem productivity Desert reflectors—polyethlene/aluminum sheets—2.7 W/m2—very expensive—could change global circulation patterns Ocean albedo—no peer reviewed studies at this point

26 Cloud-albedo enhancement Whiten clouds to increase atmospheric albedo Increase Cloud Condensation Nuclei (CCN) to change cloud albedo in marine stratus clouds (25% of ocean coverage)—more small droplets scatter more radiation than few large droplets Doubling small droplets, compensates for 2xCO2


28 Generation of sea salt fine particles by 1500 vessels needed to produce double CCN Potential to modify atmosphere/ocean circulations—effects unknown

29 Stratospheric Aerosols Inject sulphate aerosols into the stratosphere to scatter more solar radiation back to space Past volcanic eruptions have demonstrated cooling potential Particles are long-lived in the stratosphere Need 1 to 5 TgS/yr injection rate Potential large impacts (reductions ) in regional precipitation



32 Space based Solar Radiation Management Place solar shields in orbit to reflect incoming solar radiation Response will not be uniform over the globe—more reduction in tropics, less in polar regions Low earth orbit need 55,000 satellites each with 100 m2 of reflector area Solar wind forces must be offset by mass of satellite reflectors—they must be large enough to stay in place L1 high orbit position—1.5 million miles from earth—equal gravitational force from earth and sun 2% solar reduction will require 3 million km2 of reflector area

33 L2 Orbit Reflector ideas a refractor made on the Moon of a hundred million tonnes of lunar glass (Early 1989); a superfine mesh of aluminium threads, about one millionth of a millimetre thick (Teller et al.1997); a swarm of trillions of thin metallic refl ecting disks each about 50 cm in diameter, fabricated in space from near- Earth asteroids (McInnes 2002); a swarm of around ten trillion extremely thin high specification refracting disks each about 60 cm in diameter, fabricated on Earth and launched into space in stacks of a million, one stack every minute for about 30 years (Angel 2006).

34 SRM methods—quick impact upon earth temperatures


36 SRM Summary

37 Geoengineering Evaluation


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