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"Keith, David W"
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Solar geoengineering as part of an overall strategy for meeting the 1.5°C Paris target
Solar geoengineering refers to deliberately reducing net radiative forcing by reflecting some sunlight back to space, in order to reduce anthropogenic climate changes; a possible such approach would be adding aerosols to the stratosphere. If future mitigation proves insufficient to limit the rise in global mean temperature to less than 1.5°C above preindustrial, it is plausible that some additional and limited deployment of solar geoengineering could reduce climate damages. That is, these approaches could eventually be considered as part of an overall strategy to manage the risks of climate change, combining emissions reduction, net-negative emissions technologies and solar geoengineering to meet climate goals. We first provide a physical-science review of current research, research trends and some of the key gaps in knowledge that would need to be addressed to support informed decisions. Next, since few climate model simulations have considered these limited-deployment scenarios, we synthesize prior results to assess the projected response if solar geoengineering were used to limit global mean temperature to 1.5°C above preindustrial in an overshoot scenario that would otherwise peak near 3°C. While there are some important differences, the resulting climate is closer in many respects to a climate where the 1.5°C target is achieved through mitigation alone than either is to the 3°C climate with no geoengineering. This holds for both regional temperature and precipitation changes; indeed, there are no regions where a majority of models project that this moderate level of geoengineering would produce a statistically significant shift in precipitation further away from preindustrial levels.
This article is part of the theme issue 'The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.
Journal Article
A history of continental philosophy
Beginning with Kant and the earliest responses to his critical philosophy and ending with the latest developments in continental thinking across a range of disciplines, these volumes present the first coherent and comprehensive history of the continental tradition of philosophy. Divided, chronologically and thematically, into eight volumes, the \"History of Continental Philosophy\" is an indispensable resource for anyone conducting research or teaching in philosophy and related fields inthe humanities and social sciences where the influence of continental theory has been widespread. Alan Schrift has brought together an internationally renowned team of volume editors and contributors to provide an unrivalled analysis of the complex and interconnected history of continental philosophy that will become a reference point for all future work in the field.
Book
An air-liquid contactor for large-scale capture of CO2 from air
We present a conceptually simple method for optimizing the design of a gas-liquid contactor for capture of carbon dioxide from ambient air, or 'air capture'. We apply the method to a slab geometry contactor that uses components, design and fabrication methods derived from cooling towers. We use mass transfer data appropriate for capture using a strong NaOH solution, combined with engineering and cost data derived from engineering studies performed by Carbon Engineering Ltd, and find that the total costs for air contacting alone-no regeneration-can be of the order of $60 per tonne CO2. We analyse the reasons why our cost estimate diverges from that of other recent reports and conclude that the divergence arises from fundamental design choices rather than from differences in costing methodology. Finally, we review the technology risks and conclude that they can be readily addressed by prototype testing.
Journal Article
Observation-based solar and wind power capacity factors and power densities
Power density is the rate of energy generation per unit of land surface area occupied by an energy system. The power density of low-carbon energy sources will play an important role in mediating the environmental consequences of energy system decarbonization as the world transitions away from high power-density fossil fuels. All else equal, lower power densities mean larger land and environmental footprints. The power density of solar and wind power remain surprisingly uncertain: estimates of realizable generation rates per unit area for wind and solar power span 0.3-47 We m−2 and 10-120 We m−2 respectively. We refine this range using US data from 1990-2016. We estimate wind power density from primary data, and solar power density from primary plant-level data and prior datasets on capacity density. The mean power density of 411 onshore wind power plants in 2016 was 0.50 We m−2. Wind plants with the largest areas have the lowest power densities. Wind power capacity factors are increasing, but that increase is associated with a decrease in capacity densities, so power densities are stable or declining. If wind power expands away from the best locations and the areas of wind power plants keep increasing, it seems likely that wind's power density will decrease as total wind generation increases. The mean 2016 power density of 1150 solar power plants was 5.4 We m−2. Solar capacity factors and (likely) power densities are increasing with time driven, in part, by improved panel efficiencies. Wind power has a 10-fold lower power density than solar, but wind power installations directly occupy much less of the land within their boundaries. The environmental and social consequences of these divergent land occupancy patterns need further study.
Journal Article
Photophoretic levitation of engineered aerosols for geoengineering
Aerosols could be injected into the upper atmosphere to engineer the climate by scattering incident sunlight so as to produce a cooling tendency that may mitigate the risks posed by the accumulation of greenhouse gases. Analysis of climate engineering has focused on sulfate aerosols. Here I examine the possibility that engineered nanoparticles could exploit photophoretic forces, enabling more control over particle distribution and lifetime than is possible with sulfates, perhaps allowing climate engineering to be accomplished with fewer side effects. The use of electrostatic or magnetic materials enables a class of photophoretic forces not found in nature. Photophoretic levitation could loft particles above the stratosphere, reducing their capacity to interfere with ozone chemistry; and, by increasing particle lifetimes, it would reduce the need for continual replenishment of the aerosol. Moreover, particles might be engineered to drift poleward enabling albedo modification to be tailored to counter polar warming while minimizing the impact on equatorial climates.
Journal Article
Halving warming with stratospheric aerosol geoengineering moderates policy-relevant climate hazards
Stratospheric aerosol geoengineering is a proposal to artificially thicken the layer of reflective aerosols in the stratosphere and it is hoped that this may offer a means of reducing average climate changes. However, previous work has shown that it could not perfectly offset the effects of climate change and there is a concern that it may worsen climate impacts in some regions. One approach to evaluating this concern is to test whether the absolute magnitude of climate change at each location is significantly increased (exacerbated) or decreased (moderated) relative to the period just preceding deployment. In prior work it was found that halving warming with an idealized solar constant reduction would substantially reduce climate change overall, exacerbating change in a small fraction of places. Here, we test if this result holds for a more realistic representation of stratospheric aerosol geoengineering using the data from the geoengineering large ensemble (GLENS). Using a linearized scaling of GLENS we find that halving warming with stratospheric aerosols moderates important climate hazards in almost all regions. Only 1.3% of land area sees exacerbation of change in water availability, and regions that are exacerbated see wetting not drying contradicting the common assumption that solar geoengineering leads to drying in general. These results suggest that halving warming with stratospheric aerosol geoengineering could potentially reduce key climate hazards substantially while avoiding some problems associated with fully offsetting warming.
Journal Article
A temporary, moderate and responsive scenario for solar geoengineering
Solar radiation management – a form of geoengineering – could be used to cool the planet but has potential risks. A scenario for solar radiation management is proposed that is temporary, moderate and can be adjusted in light of new information.
The risks and benefits of solar geoengineering, or solar radiation management (SRM), depend on assumptions about its implementation. Claims that SRM will reduce precipitation, increase ocean acidification or deplete stratospheric ozone, or that it must be continued forever once started, are not inherent features of SRM; rather, they are features of common scenarios for its implementation. Most analyses assume, for example, that SRM would be used to stop the increase in global temperature or restore temperature to pre-industrial values. We argue that these are poor scenario choices on which to base policy-relevant judgements about SRM. As a basis for further analysis, we provide a scenario that is temporary in that its end point is zero SRM, is moderate in that it offsets only half of the growth in anthropogenic climate forcing and is responsive in that it recognizes that the amount of SRM will be adjusted in light of new information.
Journal Article
End the Deadlock on Governance of Geoengineering Research
Can scientific self-regulation control small-scale research, or is governmental regulation needed? Proposals for research on geoengineering methods to offset greenhouse-gas–driven climate change have attracted controversy ( 1 – 6 ). Multiple methods have been proposed ( 7 ), but attention and controversy have centered on methods to reduce incoming sunlight—for example, spreading reflective aerosols in the stratosphere or spraying condensation nuclei to increase low ocean clouds ( 1 , 2 ). Such high-leverage interventions offer the dual prospect of large benefits and harms. They may reduce climate-change risks faster than any other response. Yet they may also cause environmental harm or worsen policy failures—for example, undermining emissions cuts or triggering international conflict. Research is needed to develop capabilities and assess effectiveness and risks (field research as well as model and laboratory studies), but geoengineering requires competent, prudent, and legitimate governance ( 1 , 2 , 8 ). We propose specific steps to advance progress on research governance.
Journal Article
Under a not so white sky: visual impacts of stratospheric aerosol injection
Stratospheric aerosol injection (SAI) could change the sky’s appearance. This could play a role in shaping public perception of SAI. Noticeability depends strongly on tropospheric aerosol optical depth (AOD) and the amount of SAI used. We aim to quantify the noticeability of changes in sky color and brightness due to SAI. We use a 3D visible light radiative transfer package to generate cloudless sky images during high sun, sunset, and twilight under SAI from the reference point of a ground observer. We consider three aerosol types: H2SO4, CaCO3, and diamond. We consider stratospheric aerosol loadings required to produce radiative forcings of −1, −2, and −4 W m−2. We use population density and AOD data to compute the distribution of AODs people experience and then simulate sky images for the 10th, 50th, and 90th percentiles of that distribution. We compare the simulated changes in color and brightness to experimental measurements of minimum thresholds humans can detect. The three aerosol types cause similar changes, except most notably the diamond aerosol increases brightness of the solar aureole by roughly three to five times less than do H2SO4 or CaCO3. During high sun, sky whitening from sulfate SAI at −2 W m−2 is undetectable for roughly half of observers chosen randomly from the global population. For the remainder of the population, we expect whitening to still be unnoticeable for all but perhaps the most astute observers aided by color samples. Brightening and enlargement of the solar aureole is the most visible feature during high sun for H2SO4 and CaCO3, while changes near twilight would be the most noticeable impact of SAI. We cannot evaluate the fraction of the population who would notice these changes.
Journal Article