Atmospheric Structure and Dynamics: Motion and Moisture

GeoengineeringCan We Fix Climate Change?

Geoengineering DefinedGeoengineering is the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate changeWhy Geoengineering?CO2 already at 390 ppm and increasingKyoto protocol targets stabilization at 450 ppm to limit temperature change of 2 CNo evidence that nations will meet the emission reduction targets needed to stabilize at 450 ppmEmissions are actually increasing faster than projectedLarge uncertainty about tipping points (sudden thaw of the permafrost for example, very rapid loss of polar ice fields)Continued uncertainty in actual climate sensitivityLarge time lag in climate systemWhy not Geoengineering?Could reduce fragile political and public support for international mitigation effortsDivert resources from adaptation and mitigationPose significant environmental riskslarge unknownsLarge uncertainties in actual effectiveness and feasibilityRange of possible solutionswhich one? Who pays?Ethical issue: Is it morally wrong to use an artifical solution in place of reducing emissions to address climate changeThere is no regulatory frameworkwho decides to implement a geoengineering method?

How do we evaluate geoengineering methods?Royal Society Study; Geoengineering the climate: science, governance and uncertainty, 2009Evaluation criteriaEffectivenessTimelinessSafetyCostReversibilityBrief Review of Earths Energy Budget

Which components could be modified to reduce solar heating?

1% change (2.35 W/m2) produces 1.8 C surface temperature changeThe Global Carbon CycleWhich fluxes could be modified to decrease CO2 in the atmosphereDoubling of CO2 to 550 ppm equals radiative forcing of 4 W/m2 (3 C warming)

Two Primary ApproachesCarbon dioxide removal (CDR) from the atmosphereSolar radiation management (SRM) to reduce net incoming solar energyCarbon Dioxide Removal (CDR) MethodsEnhance uptake and storage by the terrestrial biosphereEnhance uptake and storage by the marine biosphereUse engineered systems to sequester carbonSolar Radiation Management MethodsSurface based modification of albedo (reflectivity) of the land or oceanTroposphere based modification of albedo (cloud modification)Upper atmosphere based modification of reflectivitySpace based engineered interception of incoming solarCarbon Dioxide Removal(CDR)BiologicalAfforestation and land useBiomass/fuels with carbon sequestrationIron/nitrogen/phosphorus fertilization of the oceanEnhance upwelling of deep ocean watersPhysicalAtmospheric CO2 scrubbersChange in ocean overturning circulationChemical (enhanced weathering)In-situ carbonation of silicates on landBasic minerals on soilOceanic alkalinity enhancement

CDR ConsiderationsSpatial scaleChemical and physical methods might require an industry as large as fossil fuel productionBiological methods might require land at a scale similar to global agricultureTemporal scaleMust approach or exceed 8.5 GtC/yr (Current emissions levels)Must be maintained for decades or centuriesMust be implemented soon to be effectiveLand-based CDR

Increase afforestation and reforestation and decrease deforestationat a scale much larger than currently exists 0.8 Gt/yr by 2030offset 2% to 4% of C emissionsBiochar and biomass methods:Harness the growth of biomass to store C

Land C sinkslong term sequestration of C in soilsBioenergy with Carbon Capture & Sequestration (not considered geoengineering)Biomass for sequestrationbury trees, crop wastes, or as charcoal biocharBiocharHeat biomass in a low or no oxygen environment to produce charcoal and syngas and bio-oilC in biochar much more stable than in organic C formsWide range of feedstocksag waste, woody residue, straw, etcAddition of biochar might improve agricultural soil productivityBetter to bury biochar or just burn biomass/biochar as a biofuel for power and heat? Could require large land areas in competition with agricultural usesLack of quantitative information and large uncertaintiesEnhanced weathering (land and oceans)CaSiO3 + CO2 == CaCO3 + SiO2 0.1 GtC/yr currently due to natural weatheringAccelerate weathering artificially on landAdd silicates to agricultural soils (7 km3 per yeartwice current coal mining rates)Impact on soil productivity is unknownCarbonate rocks used in chem engineering plants reacted with CO2 from power plantsdispose of HCO3 solutions in the oceanincreases ocean alkalinity-offsets CO2 aciditySlight increase in alkalinity could take up all excess CO2 in the atmosphereLarge scale mining, transportation, processing will be requiredCosts, environmental impacts could be large

CO2 Capture from the AtmosphereAdsorption 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 catalystfactor of 100 more effectiveAll methods require energy to move air through the adsorption systemResulting material must be transported and sequesteredCosts could be competitive since plants can be located near the sequestration location or at stranded energy sources

Oceanic Uptake of CO2Biological PumpAlgae photosynthesize CO2 in surface watersAlgae and other bio remains sink and take C to deep oceanC is respired at deep levels as CO2Effect is to pump CO2 from the surface to deep watersBiological pump is limited by nutrients needed by surface organismsLimiting 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 uncertainPerhaps 1GtC/yr could be sequestered

Carbon Dioxide Removal SummaryAll 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.Solar Radiation Management Need 1.8% (4W/m2) solar reduction to offset 2xCO2More than 1.8% is needed for lower atmosphere surface SRM SRM should have an immediate effectSRM would have immediate termination impacts

Increase surface albedo (reflectivity)Average albedo is 0.15Globally increase to 0.17, but oceans are most of the surfaceOn land, not all area can be modified so increases to as much as 1.0 are neededWhite roof of the built environmentonly 0.2 W/m2Reflective crops and grasslands1.0 W/m2 might be possiblecould reduce ecosystem productivityDesert reflectorspolyethlene/aluminum sheets2.7 W/m2very expensivecould change global circulation patternsOcean albedono peer reviewed studies at this point

Cloud-albedo enhancementWhiten clouds to increase atmospheric albedoIncrease 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 dropletsDoubling small droplets, compensates for 2xCO2

Generation of sea salt fine particles by 1500 vessels needed to produce double CCNPotential to modify atmosphere/ocean circulationseffects unknown Stratospheric AerosolsInject sulphate aerosols into the stratosphere to scatter more solar radiation back to spacePast volcanic eruptions have demonstrated cooling potentialParticles are long-lived in the stratosphere Need 1 to 5 TgS/yr injection ratePotential large impacts (reductions ) in regional precipitation

Space based Solar Radiation ManagementPlace solar shields in orbit to reflect incoming solar radiationResponse will not be uniform over the globemore reduction in tropics, less in polar regionsLow earth orbitneed 55,000 satellites each with 100 m2 of reflector area Solar wind forces must be offset by mass of satellite reflectorsthey must be large enough to stay in placeL1 high orbit position1.5 million miles from earthequal gravitational force from earth and sun2% solar reduction will require 3 million km2 of reflector area

L2 Orbit Reflector ideasa 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).

SRM methodsquick impact upon earth temperatures

SRM Summary

Geoengineering Evaluation

Geoengineering Evaluation