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3 Technical Analysis of Possible Albedo Modification Techniques
3 Technical Analysis of Possible Albedo Modification Techniques
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From page 47... ...
Two more realistic strategies (stratospheric aerosol injection and marine cloud brightening) are then discussed in greater detail because studies suggest they have the potential to produce a significant cooling and/or they have been discussed more widely in the literature.
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From page 48... ...
A spatially uniform decrease in sunlight also leads to more radiative forcing in the tropics than near the poles, because the annual mean incident solar radiation is greater in the tropics. Even if CO2 and albedo changes could cause the same change in the top-of-atmosphere energy balance, they would cause different changes in the surface energy budget; hence, any albedo modification designed to cancel out the top-of-atmosphere CO2 radiative forcing will cause changes in the surface energy budget, relative to the preindustrial state (Bala et al., 2008; Pierrehumbert, 2010, Chap.
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From page 49... ...
focused on four scenarios related to stratospheric aerosol albedo modification (Kravitz et al., 2013a) , but other experiments under this framework will add experiments on marine cloud brightening and cirrus thinning.
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From page 50... ...
This general pattern, which is robust across all solar-constant experiments, occurs because reducing the solar constant in such a way as to offset the global mean CO2 radiative forcing undercompensates this forcing in the high latitudes (where there is comparatively little sunlight to reflect) but makes up for it in the global mean by overcompensating in the more highly illuminated tropical regions.
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From page 51... ...
. Results are for all-model ensemble annual average surface air temperature differences (K)
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From page 52... ...
Figure 3.3 summarizes the global mean precipitation response in the GeoMIP G1 experiment albedo modified states. Energy is required to sustain evaporation and precipitation must ultimately balance evaporation, so the surface energy balance plays an important role in determining precipitation changes.
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One could in principle aim to compensate for CO2-associated temperature changes or precipitation changes (or some combined metric) but one could not simultaneously eliminate both global mean temperature changes and global mean precipitation changes (Ban-Weiss and Caldeira, 2010)
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averaged over years 11-50 of the simulation. Top row shows precipita Bitmappped tion, middle row shows evaporation, and bottom row shows precipitation minus evaporation.
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From page 55... ...
, with less rain falling but less rain evaporating back into the atmosphere. Globally averaged, albedo modification decreased the RMS difference in annual mean precipitation minus evaporation at grid-scale resolution by about 66 percent relative to the high-CO2 case without albedo modification; over land, albedo modification reduced RMS differences in precipitation minus evaporation by about 53 percent, despite the fact that these simulations were not designed to optimize the reduction in water delivery to land (cf.
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From page 56... ...
Figure 3.5 shows the response of the monsoon precipitation and evaporation in various regions to CO2 with and without sunlight reduction at a level that fully offsets the top-of-atmosphere energy balance from increased atmospheric CO2. The figure confirms that increased atmospheric CO2 concentrations tend to increase the strength of the monsoons, and that albedo modification has the tendency to reduce monsoon strength.
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From page 57... ...
. 2 Ocean precipitation changes between Precipitation (mm/day)
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From page 58... ...
This approach is also fairly simple to implement in a wide range of climate models. Other studies, still quite idealized, rescale an externally calculated stratospheric aerosol optical depth, incorporating the effect of inhomogeneity of aerosol distribution, evolution of the particle size, and geographical distribution of aerosols.
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to cause an albedo change sufficient to offset the radiative forcing due to a doubling or even 59
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The top panels in Figure 3.7 show the CO2 radiative forcing in the two RCP scenarios. In both scenarios, the rate of CO2 emission peaks on or before the year 2100, the rate of CO2 emission declines sharply thereafter in such a way as to keep concentration fixed for the next 200 years, and emissions cease entirely by the year 2300.
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The bottom row translates the radiative forcing trajectories of the top row into global mean temperature using the simplified energy balance model described by Pierrehumbert (2014)
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From page 62... ...
Even in the lower emission scenario -- for which the unmodified climate exceeds the 2°C target by a small amount -- to permanently avoid CO2-induced warming, the climate intervention actions would need to be maintained to nearly the year 2700. To achieve this goal for the RCP6.0 emissions scenario, albedo modification efforts would need to be maintained at a substantial level even in the year 3000, and it would in fact be several thousand years more before the CO2 radiative forcing decays to the point that climate intervention could be terminated without a substantial temperature increase.
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From page 63... ...
are possible. Because air, land, and the upper ocean respond quickly to changes in radiative forcing, an abrupt termination of albedo modification would result in rapid warming, with global mean temperatures rising within a decade or two to levels close to what would have been experienced without albedo modification (Jones et al., 2013; Matthews and Caldeira, 2007)
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From page 64... ...
Between G2 and conclude that anconditions, but rather an examinationaof the level of agree- rice production G2 Experime abrupt termination would have negligible effect on (Years 61–70) of the ment between current climate models in an idealized terin China.
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(2013) do not find any marked effect of either albedo modification or abrupt termination on the multimode mean global net primary productivity (which is often taken as a rough proxy for agricultural and ecosystem impacts)
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ALBEDO MODIFICATION STRATEGIES Climate Intervention by Stratospheric Aerosol Albedo Modification (SAAM) Climate intervention using realistic strategies involves atmospheric injection of aerosols or aerosol precursors.
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Basic Physics, Chemistry, and the Life Cycle of Stratospheric Aerosols Formation, evolution, and removal of stratospheric aerosols. Most stratospheric sulfate aerosols are formed as a result of transport into the stratosphere of natural and anthropogenic gases that contain sulfur originating nearer the surface (e.g., carbonyl sulfide, sulfur dioxide [SO2] , and sulfuric acid [H2SO4]
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. Modeling studies (Robock et Tropical Tropical Evaporation Polar Stratospheric Pipe Vortex Reservoir Condensation Transport and Coagulation -13 km Nucleation Tropopause Fold Cloud Scavenging -8 km Removal 0O 90O FIGURE 3.9 The life of natural stratospheric aerosols.
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Impacts of stratospheric aerosols on climate. Stratospheric sulfate aerosols scatter and absorb sunlight, and they also absorb and emit energy at infrared wavelengths. Their radiative impact depends on the particle size.
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The heating and changes to ozone associated with increased stratospheric aerosols can also affect tropopause temperatures with consequent effects on water vapor input to the stratosphere. The added water in the stratosphere affects the climate of the stratosphere and strato 70
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Radiative forcing by thin cirrus clouds is dominated by the greenhouse effect that produces a net positive forcing tending to warm the climate. Observations indicate the net impact of high cirrus clouds is to warm the planet, but the effect of the addition of aerosol particles on this net impact is complex to predict.
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From page 72... ...
-- produce a detectable climate response that can be used to test simulations of both aerosol forcing and the consequent response of climate, but even smaller eruptions -- the size of the Sarychev eruption (2009) -- can provide a useful test of our ability to observe and to simulate stratospheric aerosol processes (Kravitz and Robock, 2011; Kravitz et al., 2010, 2011b)
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From page 73... ...
Volcanic eruptions that inject large amounts of sulfur dioxide gas into the stratosphere are believed to have much the same effect (at least initially) as proposed methods to engineer the climate by purposeful injection of stratospheric aerosols and, thus, can serve as natural experiments for testing our understanding of albedo modification processes (Robock et al., 2010, 2013)
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The optical depth of the total stratospheric aerosols had a lifetime (for reduction by a factor of 1/e) of around 1.5 years near 19.5°N (Russell et al., 1996)
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and in cirrus cloud cover (Wylie et al., 1994) , but, ultimately, observational analyses of the aerosol effect on cirrus clouds during inatubo are P inconclusive, as pointed out by Robock et al.
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Because volcanic eruptions occur relatively infrequently, and stratospheric aerosols return to background values within a few years, volcanic impacts do not persist. Since SAAM introduces a persistent source for stratospheric aerosols, and a persistent forcing, it may involve interactions in Earth system components that are not present following volcanic eruptions, so these simulations are only an incomplete test of the relevant interactions (see Box 3.3)
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They found improved winter surface temperature responses using observed aerosol properties, specified sea surface temperatures, and quasi-biennial oscillation phase (see also Stenchikov et al., 2004)
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Notice the different scale in Figures 4a/4b and Figures 4c/4d. findings of S06 based on a selection of seven models partic- during winters following large volcanic eruptions.
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Studies involving more realistic aerosol injection scenarios are in their infancy compared to sunlight reduction studies, and details regarding the formulation of the physical processes that control aerosol forcing and response matter a lot to study conclusions. Various modeling approaches have been used to explore SAAM that tend to fall into three distinct classes, or generations, based on their level of complexity in treatment of aerosol processes.
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C L I M AT E I N T E R V E N T I O N : R E F L E C T I N G S U N L I G H T T O C O O L E A R T H FIGURE 3.12 Example of albedo modification aerosols for June, July, and August from a 20-year simulation for a 2 MtS/yr emission: (a, b) aerosol burden (g/m3 and g/m2, respectively)
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From page 81... ...
would be needed annually to maintain a radiative forcing of –4 W/m2, roughly equal to but opposite that associated with a doubling of atmospheric carbon dioxide. Studies have also explored the sensitivity of the albedo modification strategy to the characteristics of the aerosol source, changing the amplitude, source type (SO2 gas, H2SO4 gas, or sulfate particles)
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. This discussion highlights the importance of the treatment of aerosol microphysics for the development of the aerosol size distribution and the sensitivity of the albedo modification for a given injection protocol to highly uncertain aspects of the modeled aerosol microphysics.
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(2013) , which noted that volcanic eruptions that injected aerosols into the Northern Hemisphere preceded three of the four strongest years of Sahelian droughts, and their model also produced a systematic shift in tropical rainfall patterns due to stratospheric aerosol injection.
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From page 84... ...
Temperature, water vapor, and precipitation. As in the idealized experiments, model simulations suggest that if stratospheric aerosol albedo modifications were increased to compensate for a forcing from a doubling or quadrupling of CO2, equatorial surface temperatures would be somewhat cooler than an unperturbed planet, polar temperatures somewhat warmer, global averaged precipitation would likely be reduced, and the planetary response to SAAM termination would be much like that described in 84
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From page 85... ...
(2012) noted that increases in stratospheric aerosol loadings will likely lead to an increased upper tropospheric temperature, stabilizing the upper troposphere, decreasing vertical velocity, and ultimately reducing ice crystal nucleation rates and producing optically thinner cirrus clouds.
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In particular, the high-latitude response to stratospheric aerosol injection was much weaker in the simulations with a resolved stratosphere than in simulations that did not adequately compute the stratospheric response. The weakened polar response implies a less effective offset of CO2-induced 86
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From page 87... ...
not intended to entirely counter the radiative forcing by greenhouse gases. In these simulations, aerosol injection delays, but does not prevent, the ultimate loss of September Arctic sea ice.
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From page 88... ...
, averaged over years 11-50 of the simulation. For these panels, "abrupt4xCO2" is a climate with a quadrupling of the CO2 concentration, "G1" is a climate with a quadrupled CO2 and a reduction in sunlight sufficient to return the global average surface 3-13 Figure temperature to a reference state, and "piControl" is the preindustrial climate.
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From page 89... ...
indicate that, at global scale, albedo modification by stratospheric aerosols in a high-CO2 world would have little detectable effect on land biological productivity in most places but could in some places cause significant increases or decreases in land biological productivity. Relative to the preindustrial state, a high-CO2 world with albedo modification is projected to have higher biological productivity in nearly all land areas, largely due to CO2 fertilization.
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From page 90... ...
This would include quantifying the amount of source material (SO2 or sulfuric acid) injected, its rate and direction of spread with time, the formation of H2SO4, the size of the particles formed, their effect on cirrus clouds, and their effect on Earth's radiation budget.
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As noted in the section examining the processes that produce H2SO4, it might be important to also obtain measurements of the aerosol size distribution in order to 3 Moderate Resolution Imaging Spectroradiometer. 4 Multi-angle Imaging SpectroRadiometer.
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. Environmental Consequences of SAAM A variety of consequences are anticipated to arise from significant changes in stratospheric aerosols.
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Advanced preparation will be needed if scientists are to make the best use of the next major volcanic eruption. Although Pinatubo is the best characterized eruption to date, ironically our ability to monitor stratospheric aerosols has deteriorated since that time, with the loss of the Stratospheric Aerosol and Gas Experiment (SAGE)
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. There may also be a role for selective deployment of ground-based and airborne radiometers for the purposes of refining estimates of the amount of solar radiation transmitted through the stratospheric aerosol mass.
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Sunlight reduction could also affect home heating and solar power facilities. • Introduction of stratospheric aerosols is likely to slightly increase the acid ity of the snow and rain reaching the surface.
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as the plume disperses. These characteristics influence decisions about the strategy of delivery and govern the efficacy of the strategy (radiative forcing per unit emission of sulfur)
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The cost of a responsible deployment strategy involves not just the cost of aerosol injection, but the cost of observing systems and infrastructure to detect and attribute the magnitude of and response to albedo changes from stratospheric aerosol injection. Estimating the full costs of an observing system and infrastructure to do this was beyond the charge of this committee, but these costs are generally estimated to be significant, as typical satellite deployment costs often run into the billions of dollars.
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; • impacts on chemistry (particularly ozone) ; • impacts on water vapor in the upper troposphere and lower stratosphere; and • effects of additional aerosol on upper tropospheric clouds.
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From page 99... ...
interactions of SAAM with dominant modes of interannual variability, volcanic eruptions, and other unpredictable or unpredicted events; (d) dynamic influences of the stratosphere on the troposphere, as they seem to have the capability for profoundly influenc ing the nature of high-latitude response, and therefore sea ice and glaciers.
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This capability would involve space-borne capabilities for monitoring stratospheric aerosols (which would of necessity be multiple use, since large volcanic eruptions are infrequent) and rapidly deploy able ground-based and airborne instruments.
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From page 101... ...
Albedo Modification by Marine Cloud Brightening Low clouds, particularly over dark ocean surfaces, play a very important role in Earth's energy budget by scattering sunlight back to space that would otherwise reach and warm the surface. Because of the low albedo of the ocean surface and the "whiteness" of ocean clouds that very efficiently reflect sunlight back to space, rather modest changes in cloud albedo, cloud lifetime, or cloud areal extent might produce significant changes to both local and planetary albedo (Slingo, 1990)
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From page 102... ...
are called cloud condensation nuclei. Aerosol particles that take up water vapor more readily form cloud drops more easily than those that do not, and larger hydrophilic particles "compete" with other particles, growing to cloud drops rapidly in a saturated air mass and eventually either forming precipitation or evaporating after they are exposed to unsaturated air for a time.
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From page 103... ...
. The short particle lifetimes make it possible to produce big local changes to the cloud albedo and radiative forcing that vary significantly in space and time, a signature that is quite different from the idealized forcing distributions discussed in sunlight reduction studies and stratospheric aerosol albedo modification strategies where the aerosol forcing can spread globally or across most of a hemisphere.
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From page 104... ...
. Purple indicates regions where clouds are not particularly susceptible to aerosol effects; red indicates clouds that are susceptible.
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From page 105... ...
experiments in the atmosphere are likely to provide better constraints for comparison to model behavior. Observations of Marine Cloud Brightening There is ample evidence that cloud albedo is strongly affected by aerosol particles and that mankind is able to influence the albedo of clouds.
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From page 106... ...
. There are existing commercial and experiment-specific examples of cloud albedo modification that can be used to provide both an observational signature of cloud albedo modification and proof of concept of the particle emission and scavenging rates that can be expected in typical marine boundary layers.
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From page 107... ...
One interesting result of this study is that the cloud albedo modification was effective only a very small fraction of the time, even in clouds that are classified by satellite and models as likely to be susceptible. This provides preliminary but nonscalable data on how much additional particle emissions would be needed to achieve the intended effect on planetary albedo compared to what is currently implemented in global models.
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From page 108... ...
DYCOMS II Stevens et al., 2003 Characterization of POCs in nocturnal marine boundary layers. (Nocturnal)
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From page 109... ...
2012 Coggon et al., 2012 Wide-reaching impacts of ship-emitted particles. Chen et al., 2012 Reversed cloud albedo effect in some ship tracks.
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, and aerosols would need to be replenished on an ongoing basis over a large area. The footprint of cloud albedo modification of stratocumulus clouds by controlled emissions could involve just one ship (with speed 10 to 20 kts)
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From page 111... ...
suggested that seawater might be exploited as a source of small seawater droplets to be injected into the boundary layer, where they could evaporate and form small sea salt particles; sulfate aerosols produced by fertilization of arine biota, and organic aerosols produced by combustion have also been sug m gested (Wingenter et al., 2007)
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From page 112... ...
that their reflectance may be modified by aerosol particles, the formation of "tracks" with 112
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. Modeled Climate System Responses to Marine Cloud Brightening Producing a realistic representation of clouds and aerosols (and their interactions)
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(2013) used ultrahigh-resolution and plume models to account for coagulation of aerosol particles after they were emitted and concluded that plume-scale coagulation could reduce the efficacy of marine cloud brightening by almost 50 percent.
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From page 115... ...
and found that up to 35 percent of the radiative forcing due to current levels of greenhouse gases could be offset by a very aggressive level of stratocumulus modification (~1 W/m2) that delayed the warming by ~25 years (average reduction in energy reaching the surface of the seeded regions of about 30 W/m2)
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Some models prescribed aerosol distributions and did not allow cloud processes to remove aerosols; others allowed those interactions to take place and used more complex treatments of aerosol-cloud interactions. Each model accounted for some direct and indirect radiative effects of the emitted sea salt aerosol particles.
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(2011) directly compared the model differences in forcing and response between stratospheric aerosols and marine cloud brightening.
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From page 118... ...
Global models disagree in their predictions about MCB effects on the spatial distribution and intensity of precipitation, particularly when the MCB global average forcing exceeds 0.5 W/m2 annual average. Observational Requirements for Characterizing Marine Cloud Brightening There are three types of observations that are needed to track and quantify the radiative effects of particles on cloud albedo: satellite reflectance sensors, described elow; b in situ aerosol and cloud instrumentation; and logistical metrics.
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com) , the most obvious evidence for cloud albedo modification can be collected from emissions from controlled ships that "zig-zag" back and forth instead of transiting effi ciently from one port to another (typically along standard shipping routes)
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(2011) estimated that using MCB at amplitudes sufficient to alter climate would decrease annual mean sunlight reaching the surface by 30 to 50 W/m2 (~20 percent, approximately doubling cloud radiative forcing)
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From page 121... ...
Theory, modeling, and observations indicate that the susceptibility of cloud albedo to increases in aerosol particle concentrations saturates, but the point of diminishing returns varies with cloud type and background aerosol amount. The natural variability of clouds is high, and many different cloud regimes exist that may respond differently to aerosol increases, complicating signature detection and making quantitative characterization of cloud susceptibility and effective radiative forcing (ERF)
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From page 122... ...
Delivery mechanisms. Although aerosol production and delivery issues are not expected to be the limiting factor for implementing MCB albedo modification strategies (Russell et al., 2013) , at least three methods have been considered for delivering suitable aerosols into the marine boundary layer to brighten clouds.
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From page 123... ...
due to the engineering considerations in marine conditions, such as clogging from impurities of source material. Efficacy. Current estimates of the long-term and large-scale efficacy of the MCB strategy (e.g., the radiative forcing per unit aerosol emission for different marine cloud regions)
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From page 124... ...
Costs. Table 3.3 provides estimates of the potential costs and resources required for various levels of cloud albedo modification activity. Summary and Statement of Research Needs for Marine Cloud Brightening Research beyond the use of computational models is needed to address some of the key open questions on the potential for marine cloud brightening to be useful for a lbedo modification purposes.
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From page 125... ...
Opportunities to improve understanding of relevant processes that can potentially be revealed much more clearly with small-scale controlled emissions studies include the following: • Comparing to a control. Monitoring adjacent air masses or air masses prior to and following emissions would serve as an experimental control to contrast with the seeded clouds, and monitoring both the perturbed and control air masses would help identify the sensitivity to preexisting air mass properties (e.g., aerosol amount)
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From page 126... ...
Studies using deliberately controlled emissions for hours or possibly for days, covering regions of varying areas, differing release durations and start times, or changing particle types would provide observations of the resulting differences in dynamic responses to s eeding, providing information on cloud clearing, sensitivity to diurnal varia tion in the boundary layer, sensitivity to composition or size distribution of emissions, and so on. These effects probably operate nonlinearly to dampen or increase the brightening.
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From page 127... ...
Other Methods There are a number of other proposed techniques that are often considered in discussions of climate intervention broadly that also have to do with modifying the albedo and/or radiation balance of the planet. The proposals in this section have generally shown less promise in initial studies, are less developed than the ones described in the earlier sections of this chapter, or are only mentioned in passing in the literature.
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From page 128... ...
All published estimates in the previous literature suggest that changing planetary albedo by whitening rooftops cannot compensate for a significant fraction of the forcing produced by present or future anthropogenic forcing by greenhouse gas emissions (e.g., GAO, 2011; The Royal Society, 2009)
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There are also serious unanswered questions about how this would affect desert ecosystems as well as atmospheric circulation and precipitation patterns, including potential effects on monsoons (The Royal Society, 2009)
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From page 130... ...
suggest that small increases to long-wavelength radiation to space could offset the enhanced radiative forcing due to a CO2 doubling. As discussed by Cotton (2008)
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From page 131... ...
Research supporting possible cirrus cloud modification will also be relevant to better understanding the effects of stratospheric aerosol injection -- either from volcanic eruptions or from stratospheric albedo modification efforts -- because these aerosols will eventually settle out of the stratosphere into the upper troposphere where cirrus clouds reside (Cirisan et al., 2013; K uebbeler et al., 2012)
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From page 132... ...
Satellite Monitoring of Large-Scale Direct Effects of Albedo Modification A minimal requirement for controlled deployment of a climate intervention involving albedo modification is that one be able to detect and characterize the actual change in albedo achieved by the intervention. This is crucial, because the chain of physical processes linking the controlled injection of a substance into the atmosphere to the resulting change in albedo is so complex, and involves so many stacked uncertainties, that it is unlikely to prove possible to accurately compute the albedo change a priori.
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From page 133... ...
Since that finding is made in the context of an approximate 2.4 W/m2 of radiative forcing by anthropogenic greenhouse gases, it is clear that the current monitoring capabilities fall far short of what would needed in the −1 W/m2 gradualist scenario, let alone smaller-scale field trials, and would be of questionable adequacy even for a full-scale deployment. Currently, monitoring of Earth's top-of-atmosphere radiation budget relies primarily on the CERES instrument, which has flown on a series of satellites and is still operational on NASA's Aqua and Terra satellites and the Suomi NPP satellite at the time of writing.
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From page 134... ...
underlying snow and ice cover. Information of this type would be valuable in assessing the changes in cloud albedo achieved by boundary layer cloud-brightening schemes, as well as for characterizing unintended effects of stratospheric aerosol injection on upper tropospheric clouds.
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From page 135... ...
Albedo feedbacks arising from changes in clouds and sea ice are addressed by the measurements described in the previous section, but beyond that it is necessary to monitor the outgoing infrared radiation, which determines the rate at which Earth loses energy to space. The outgoing infrared flux is affected by the response of clouds, water vapor, and temperature of both the surface and the atmosphere, and accurate monitoring is a crucial part of determining the way a climate intervention has altered Earth's energy budget.
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Consequently it is necessary to have a system that observes such p arameters as ecosystem health (stress) and dynamics, soil moisture, precipitation, oceanic thermodynamic and dynamic response to a modified energy balance, and other variables.
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. Current Observational Capabilities and Needs for Future Continuity of Observations Monitoring of Earth's TOA energy budget is at present provided primarily by the CERES suite of instruments, flying on NASA's Terra and Aqua satellites and the Suomi NPP 137
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The failure of the current observing capability to quantify the radiative forcing associated with anthropogenic emissions is consistent with the conclusion that the current observational capability to observe and understand climate forcing associated with albedo modification strategies is lacking (see also Robock, 2014)
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From page 139... ...
introduction of stratospheric aerosols and (2) increasing the reflectivity of low clouds (marine cloud brightening)
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From page 140... ...
Research and observational programs in this category include improved monitoring of Earth's radiation budget and improved understanding of aerosols and their effect on clouds. An extensive set of recommendations describing modeling and field studies that can be used to improve understanding of relevant processes, and potential consequences from albedo modification, can be found in the earlier sections titled "Summary and Statement of Research Needs for SAAM" and "Summary and Statement of Research Needs for Marine Cloud Brightening" and in Box 5.1 of Chapter 5.
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From page 141... ...
For support of albedo modification research, hyperspectral short-wavelength measurements are particularly important, but hyperspectral long-wavelength measurements can help discriminate cloud changes and may also be useful in monitoring stratospheric heating due to aerosols. • Maintaining continuity of the existing Argo float system for continued and sustained monitoring of ocean heat uptake is a crucial part of monitoring the energy budget, as it is the prime source of information about heat exchange between the atmosphere and ocean.
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From page 142... ...
The entries on the tables are the product of committee deliberation based on an understanding of the available literature. The table goes into detail for the two strategies that were discussed in detail: stratospheric sulfate aerosol injection and marine cloud brightening.
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From page 143... ...
: technology exists at scale Intermediate-maturity technology: prototypes exists, not to scale Immature technology (not ready to deploy quickly, high technical risk) : needs prototyping Technological readiness (device level maturity)
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From page 144... ...
Slow: centuries (i.e., >100 years) Time for direct radiative effects to dissipate if albedo modification activity is suddenly stoppedc Slow: 1-5 years Medium: 1-5 months Fast: 1-5 days Relative costs of an albedo modification deviced (orders of magnitude; when building at scale)
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From page 145... ...
Technical Analysis of Possible Albedo Modification Techniques TABLE 3.4 Continued Stratospheric Marine Aerosol Albedo Cloud Modification Brightening Ability to detect unsanctioned albedo modification at scalef Easily verifiable: existing and planned observation systems can verify without retasking Moderately easy to verify: existing observation systems would need retasking or known technology would need to be deployed Difficult to verify: new technology/methods would need to be developed/deployed Ability to measure the radiative forcing of a large-scale, decade-long albedo modification deployment with sufficient accuracy Easily verifiable: existing and planned observation systems can verify without retasking Moderately easy to verify: existing observation systems would need retasking or known technology would need to be deployed; using substantial additional resources employing existing technology Difficult to verify: new technology/methods would need to be developed/deployed Ability to monitor and attribute the climate response of a large-scale, decade-long albedo modification deployment with sufficient accuracy Easily verifiable: existing and planned observation systems can verify without retasking Moderately easy to verify: existing observation systems would need retasking or known technology would need to be deployed; using substantial additional resources employing existing technology Difficult to verify: new technology/methods would need to be developed/deployed continued 145
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C L I M AT E I N T E R V E N T I O N : R E F L E C T I N G S U N L I G H T T O C O O L E A R T H TABLE 3.4 Continued Stratospheric Marine Aerosol Albedo Cloud Modification Brightening Environmental consequences and risks (geographic extent of impact, adverse consequences, co-benefits) g,h Local-scale consequences Regional-scale consequences Global-scale consequences Addresses nonwarming effects of CO2 (e.g., ocean acidification, CO2 fertilization)
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From page 147... ...
f This is likely not a climate signal, but would rather be a logistical signal (i.e., deployment of large numbers of planes to the stratosphere or large numbers of ships) and the resulting stratospheric aerosol cloud (with lidar)
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