Climate Intervention Reflecting Sunlight to Cool Earth (2015) / Chapter Skim
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2 Climate Intervention by Modifying Earth's Albedo
2 Climate Intervention by Modifying Earth's Albedo
Pages 29-46
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From page 29... ...
For example, in the temperate and polar regions, winter temperatures are generally colder than summer temperatures, because those regions receive less sunlight in the winter. The energy principles controlling temperature on a hot day or cool night result from and influence weather on a day-to-day local scale and also operate on climate at seasonal through millennial timescales over the globe.
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From page 30... ...
. Many early weather modification proposals did not move beyond the discussion stage, and the ones that did mostly did not produce the desired effects on the physical environment.
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From page 31... ...
Proposed weather modification projects included ideas such as cloud-seeding techniques, weakening hurricanes with biodegradable oil slicks, and breaking up polar ice with nuclear weapons, often as part of the Cold War quest to militarize the atmosphere (Fleming, 2010b; Hoffman, 2002, 2004)
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From page 32... ...
SOME BASIC PHYSICS CONCERNING CLIMATE INTERVENTION BY ALBEDO MODIFICATION It has been known since the work of Fourier in the early 1800s that the temperature of Earth is determined by the requirement that, in steady state, the rate at which energy is lost to space in the form of outgoing infrared radiation balances the rate at which energy in the form of incoming solar radiation is absorbed by Earth. A mismatch in this balance would cause Earth to warm or cool.
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From page 33... ...
is reduced relative to the preindustrial climate, but the effect on the energy budget is offset by a corresponding reduction in the amount of solar energy absorbed. The solar absorption is reduced by increasing the albedo so as to reflect more sunlight back to space.
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From page 34... ...
In differing ways, they also influence regional temperatures, the global hydrological cycle, land plants, and other components of the Earth system. So, turning up one knob and turning down the other might be able to restore Earth's global mean temperature but could nevertheless produce substantial changes to Earth's environment (see Chapter 3 for further discussions)
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From page 35... ...
Figure 2-2 Bitmapped change in albedo can in theory be accomplished by maintaining a small mass of aerosols in the atmosphere; this is the chief appeal of climate intervention by aerosol injections. To put the required increase in albedo into perspective, the 1991 Pinatubo eruption, which is estimated to have been the largest eruption since Krakatau in 1883, led to a radiative forcing of approximately −3 W/m2 within a month following the eruption, decreasing to nearly zero over the subsequent 2 years (IPCC, 2007b, Fig.
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From page 36... ...
The longwavelength component refers to changes in the amount of infrared radiation emitted by Earth to space and is controlled primarily by changes in the greenhouse gas content of the atmosphere. The short-wavelength component refers to changes in the amount of solar energy absorbed by Earth and is controlled primarily by the proportion of sunlight reflected back to space by the atmosphere and the surface.
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From page 37... ...
Should it ever become important for society to cool Earth rapidly, albedo modification approaches (in particular stratospheric aerosol injection and possibly marine cloud brightening) are the only ways that have been suggested by which humans could potentially cool Earth within years after deployment. Over the past 15 years, stratospheric aerosol injection and marine cloud-brightening ideas were tested in modern climate models, and results for an idealized set of scenarios across a broad spectrum of models (Kravitz et al., 2013a)
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From page 38... ...
Finally, as a matter of physical and economic capability, a single nation, a large corporation, or a group of individuals with sufficient means could potentially deploy albedo modification in the absence of an international consensus or coordination (Bodansky, 2011; Victor et al., 2009)
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From page 39... ...
COMPARISON OF SOME BASIC RISKS ASSOCIATED WITH ALBEDO MODIFICATION The increase in greenhouse gas concentrations from anthropogenic emissions intro duces many risks to the planet. Deploying albedo modification could produce a generally cooler climate, but it would introduce risks of a different type.
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From page 40... ...
The atmosphere and ocean respond to radiative forcing by redistributing the heat in a way that alleviates the mismatch, but this requires changes in circulation patterns and also can leave regional climate anomalies uncompensated to one extent or another. Additionally, increasing albedo alters the surface energy budget by reflecting sunlight that would otherwise sustain evaporation (and hence precipitation)
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From page 41... ...
The magnitude of ocean acidification and biological impacts is related to the concentration and growth rate of excess atmospheric carbon dioxide. Thus, approaches for mitigating future ocean acidification impacts require curbing human carbon dioxide emissions to the atmosphere and/or developing atmospheric carbon dioxide removal and sequestration methods.
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From page 42... ...
Additional considerations apply specifically to albedo modification techniques that involve stratospheric aerosols. Stratospheric aerosols heat the stratosphere at the same time they cool the surface, which can have important implications for the climate of both the stratosphere and the surface, as well as for stratospheric chemistry (see further discussion in Box 3.2 and stratospheric aerosol modeling sections in Chapter 3)
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From page 43... ...
These issues are discussed at length in Chapter 3. OVERVIEW OF THE ALBEDO MODIFICATION ASSESSMENT Rather than discuss every potential means of modifying Earth's albedo that has been proposed, this report focuses on the two strategies that have received the most attention and which may most feasibly have a substantial climate impact: stratospheric aerosol injection and marine cloud brightening.
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From page 44... ...
As described in the Chapter 3 section "Other Methods," these other proposed techniques are generally either prohibitively expensive or difficult to scale to the point where they could offset a substantial amount of CO2 radiative forcing. Proposals to modify cirrus clouds, which are not formally an albedo modification method but use another means to modify the planet's energy balance, have received less attention thus far and are also discussed briefly in this section.
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From page 45... ...
Though the chief recommended actions in this report are to move forward with research but not with deployment, expansion of research in albedo modification is not without risk, and most of the risks are sociopolitical in nature; on the other hand, ignorance (through failure to carry out research) of consequences of albedo modification deployment also entails considerable risk.
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