Article

# Space-based solar shield to offset greenhouse effect

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## Abstract

The construction of a thin glass shield is proposed to offset the greenhouse effects caused by CO2 buildup in the earth's atmosphere. It is suggested that the shield could be built from lunar materials and should be located near the first Lagrange point of the earth-sun system. Consideration is given to the photon thrust of the shield, the shield size, effective blockage, and possibilities for shield design.

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... This can be achieved in two ways: (1) reducing the amount of solar radiation reaching the Earth and (2) increasing the reflectivity of the planet. Sunlight reaching the Earth can be reduced by space-based reflectors (Angel 2006;Early 1989;Seifritz 1989;Struck 2007). The reflectivity of the planet can be increased by increasing the albedo of persistent marine low clouds (Latham 1990;Latham et al. 2008) or enhancing the reflectivity of the land surface by whitening the roofs in urban areas (Akbari et al. 2009) or making the ocean surface more reflective (Evans et al. 2010). ...
... Placement of reflecting mirrors, sunshades, and a cloud of small spacecrafts at L1 Lagrange point between the Earth and Sun has been suggested (Angel 2006;Early 1989;Seifritz 1989) as one of several space-based SRM options. At the L1 point, the gravitational forces of the Sun and Earth cancel each other exactly, and therefore, it is a stationary point where reflectors could be maintained at a minimal cost. ...
... L1 point is at a distance of 1.5 Â 10 6 km from the Earth, about four times the distance between the Moon and the Earth. Early (1989) proposed the construction of a thin glass shield made from lunar materials and located near the L1 point of the Earth-Sun system (Early 1989). Earlier estimates (Seifritz 1989) suggested that a reduction in surface temperature of the planet by 2.5 K would require the reflection of the solar radiation by 3.5 %. ...
Chapter
The accelerated rate of increase in atmospheric CO2 concentrations in recent years and the inability of humankind to move away from carbon-based energy system have led to the revival of the idea of counteracting global warming through geoengineering schemes. Two categories of geoengineering proposals have been suggested: solar radiation management (SRM) and carbon dioxide removal (CDR) methods. SRM schemes would attempt to reduce the amount of solar radiation absorbed by our planet. Placing reflectors or mirrors in space, injecting aerosols into the stratosphere, and enhancing the albedo of marine clouds are some of the proposed SRM methods. In this section, the various space-based SRM methods which are likely to reduce the incoming solar radiation uniformly across the globe are discussed. In the past decade, the effects of these space sunshades on the climate system have been simulated using climate models by reducing the amount of incoming solar radiation by appropriate amounts (reduced solar constant). Key modeling results on the extent of global and regional climate change mitigation, unintended side effects, and unmitigated effects are briefly discussed.
... Effect of photon pressure Seifritz [8] proposed reflecting 3.5% of the Sun's energy at L1 with a metallic shade covering an area of 4.5 × 10 6 km 2 . Early [12] showed that pressure from sunlight falling on the shade can be significant for the low-density shade structures envisioned. Fortunately, this force can be counterbalanced by moving the shade closer to the Sun than the nominal L1 point, producing a gravity imbalance that offsets the force of photons pushing the shade earthward. ...
... Early [12] also proposed reducing photon pressure by making the shade a transparent possible with a well-designed elliptical orbit. ...
... Several ideas have been proposed for the lightweight membranes needed to refract incident sunlight away from Earth. These include 10 µ thick glass panels using Fresnel prisms for deflection [12], diaphanous metallic mesh gratings [7], and a layered silicon nitride structure to diffract sunlight with low reflectivity [14]. The fabrication and testing of these and other candidates should be a near-term priority. ...
... A lower r allows the starshade to be placed closer to L1, and to be smaller and less massive. Early (1989) showed that the key to low r is to scatter light at an angle just sufficient to miss the planet, rather than reflect it (this will be revisited in Sec. 3.5). ...
... that avoids the planet but minimizes the transfer of momentum to the starshade (proportional to θ 2 ) and thus minimizes the required mass (Early 1989, Fig. 1). This will contribute to the lightcurve at phases outside of transit. ...
Article
All water-covered rocky planets in the inner habitable zones of solar-type stars will inevitably experience a catastrophic runaway climate due to increasing stellar luminosity and limits to outgoing infrared radiation from wet greenhouse atmospheres. Reflectors or scatterers placed near Earth's inner Lagrange point (L1) have been proposed as a 'geo-engineering" solution to anthropogenic climate change and an advanced version of this could modulate incident irradiation over many Gyr or "rescue" a planet from the interior of the habitable zone. The distance of the starshade from the planet that minimizes its mass is 1.6 times the Earth-L1 distance. Such a starshade would have to be similar in size to the planet and the mutual occultations during planetary transits could produce a characteristic maximum at mid-transit in the light-curve. Because of a fortuitous ratio of densities, Earth-size planets around G dwarf stars present the best opportunity to detect such an artifact. The signal would be persistent and is potentially detectable by a future space photometry mission to characterize transiting planets. The signal could be distinguished from natural phenomenon, i.e. starspots or cometary dust clouds, by its shape, persistence, and transmission spectrum.
... They envision large space-based objects, which might be manufactured on the moon, mining local materials, or using material from asteroids. Concepts of giant lenses (Early 1989), dust rings (Bewick et al. 2013), and sunshades (Kosugi 2010) to block part of the Sun's incoming radiation using the effects of reflection, absorption, and diffraction were worked out. A convex lens with 1,000 km in diameter is considered sufficient, and in a Fresnel embodiment, it would only be a few millimeters thick (Early 1989). ...
... Concepts of giant lenses (Early 1989), dust rings (Bewick et al. 2013), and sunshades (Kosugi 2010) to block part of the Sun's incoming radiation using the effects of reflection, absorption, and diffraction were worked out. A convex lens with 1,000 km in diameter is considered sufficient, and in a Fresnel embodiment, it would only be a few millimeters thick (Early 1989). Shading the Sun by approx. ...
Chapter
Full-text available
Engineering the climate by means of carbon dioxide removal (CDR), Earth radiation management (ERM), and/or solar radiation management (SRM) approaches has recaptured the attention of scientists, policy makers, and the public. Climate engineering is being assessed as a set of tools to deliberately, and on a large scale, moderate or retard global warming. There are several concepts available, like injecting aerosol-forming SO2 into the stratosphere or placing huge objects in orbit to partly shade Earth from incoming radiation or fertilizing the ocean with iron for increased algae growth and creation of carbon sinks. Such concepts are highly speculative, and irrespective of whether they would work, they bear huge risks, from adversely affecting the complex climate system on a regional or global scale to potentially triggering droughts, famine, or wars. More research is needed to better understand promising concepts and to work them out in depth, so that options are made available in case they should become necessary in the future, when climate change mitigation and adaptation measures do not suffice and fast action becomes imperative. Apart from the technological hurdles, which are anyhow mostly far beyond today’s engineering capabilities, huge social, moral, and political issues would have to be overcome. The purpose of this chapter is to highlight a few common concepts of CDR, ERM, and SRM for climate engineering to mitigate climate change.
... Here, we use an atmosphere-ocean chemistry-climate model to study atmospheric composition changes for one of the most common geoengineering modelling experiments: the reflection of solar energy before it can enter the Earth's atmosphere, an idea often depicted by the use of space mirrors (Early, 1989;Seifritz, 1989). This idealized geoengineering experiment belongs to methods subsumed under the term solar radiation management (SRM). ...
... In the G1 experiment the effect of an abrupt quadrupling of atmospheric carbon dioxide (CO 2 ) on the global mean surface temperature is approximately offset by reducing the model's solar constant. This can be thought of as an experiment in which space-mirrors reflect sunlight before it enters the Earth's atmosphere (Early, 1989;Seifritz, 1989). Starting from approximately pre-industrial concentrations with atmospheric CO 2 at ∼ 285 ppmv (piControl), we thus carried out, firstly, an abrupt 4 × CO 2 experiment, in which atmospheric CO 2 is instantaneously quadrupled to ∼ 1140 ppmv and, secondly, a G1 type experiment in which the global warming caused by 4 × CO 2 was offset by a solar irradiance reduction of 49.0 Wm −2 (∼ 3.6 %). ...
Article
Full-text available
Various forms of geoengineering have been proposed to counter anthropogenic climate change. Methods which aim to modify the Earth's energy balance by reducing insolation are often subsumed under the term solar radiation management (SRM). Here, we present results of a standard SRM modelling experiment in which the incoming solar irradiance is reduced to offset the global mean warming induced by a quadrupling of atmospheric carbon dioxide. For the first time in an atmosphere–ocean coupled climate model, we include atmospheric composition feedbacks for this experiment. While the SRM scheme considered here could offset greenhouse gas induced global mean surface warming, it leads to important changes in atmospheric composition. We find large stratospheric ozone increases that induce significant reductions in surface UV-B irradiance, which would have implications for vitamin D production. In addition, the higher stratospheric ozone levels lead to decreased ozone photolysis in the troposphere. In combination with lower atmospheric specific humidity under SRM, this results in overall surface ozone concentration increases in the idealized G1 experiment. Both UV-B and surface ozone changes are important for human health. We therefore highlight that both stratospheric and tropospheric ozone changes must be considered in the assessment of any SRM scheme, due to their important roles in regulating UV exposure and air quality
... At the same time, moving the sunshade towards the Sun increases the minimum area for reducing solar radiation and the overall mass of the system. Researchers (Early, 1989;McInnes, 2000McInnes, , 2006McInnes, ,2010Angel, 2006;Fuglesang and Herreros, 2021) have proposed different designs for sunshade systems composed of swarms of small occulting membranes. The main difference of their designs is the value of the reflectivity "k", from equation 3, which is a function of the optical properties of the sunshade. ...
... When η and ε are zero, k equals 0.17. The authors Early (1989) and Angel (2006) reduced k, and thus sunshade radiation pressure and mass, by increasing transmissivity in their occulting membrane designs. In Figure 2, the weight and location of different sunshade designs with different "k" values are compared. ...
Preprint
Limiting climate change to within the 2 {\deg}C limit requires net zero emissions of CO2 by 2050. However, the window of opportunity is closing fast. Geoengineering is the intentional and large-scale manipulation of the environment and the climate, in particular. It is increasingly discussed as a complement to ongoing mitigation efforts. As a particular geoengineering approach, space-based geoengineering blocks or dissipates a fraction of incoming sunlight via a large number of occulting membranes, located close to the Sun and the Earth Lagrange 1 point. However, the mass of these sunshades, around $10^7$-$10^8$ tons, and their deployment cost and effort render them about $10^3$ times more costly than terrestrial alternatives. In this article, an affordable zero-radiation pressure sunshade to be positioned in L1 of the Earth-Sun system is proposed, which is between $10^2$ to $10^3$ times lighter than the lightest existing sunshade concepts. This is achieved via a net zero-radiation pressure design, allowing for using extremely lightweight materials. The whole sunshade system has a total mass of approximately $6.2 \times 10^5$ tons and its deployment requires between $10^2$ to $10^3$ annual launches during a ten-year period.
... For purely radiation management purposes, we do not really care if we have a million small sails a kilometre square each or one great monolithic sail of a million square kilometres. For example, Early (1989) estimated that a single sail made of lunar glass on the order of 2000 km diameter at SEL1 would be necessary to overcome a forecast +2% increase (~+27 W m -2 ) in Earth's total "radiative forcing function" [44]. Hudson (1991) estimated a parasol mass of 150 million tonnes for a notional 1% reduction, not inconsistent with our mass estimates in Table 2, as well as figured out the important drivers and dependencies. ...
... For purely radiation management purposes, we do not really care if we have a million small sails a kilometre square each or one great monolithic sail of a million square kilometres. For example, Early (1989) estimated that a single sail made of lunar glass on the order of 2000 km diameter at SEL1 would be necessary to overcome a forecast +2% increase (~+27 W m -2 ) in Earth's total "radiative forcing function" [44]. Hudson (1991) estimated a parasol mass of 150 million tonnes for a notional 1% reduction, not inconsistent with our mass estimates in Table 2, as well as figured out the important drivers and dependencies. ...
Article
No study of coping with climate change is complete without considering geoengineering. A Dyson Dot is one or more large (Earea ̃700 K km 2, >200 megatonne) lightsail(s) in a radiation-levitated non-Keplerian orbit(s) just sunward of the Sun-Earth Lagrange-1 point. The purpose of this syncretic concept is twofold: (I) As a parasol, it would reduce insolation on Earth by at least one-quarter of a percent (-3.4 W nr -2), same as what caused 1.5°C drop during the Little Ice Age (̃1550-1850) and same as the IPCC Third Report's mid-range value for global warming by 2050. The parasol transforms the solar constant to a controlled solar variable. (II) Hosting a ̃50K km2 photovoltaic power station on its sunny side and relaying beamed power via maser to rectennas on a circumpolar Dymaxion grid, the system could displace over 300 EJ/a (̃100 trillion kWh/yr) of fossil-fired power (total global demand for electricity forecast by 2050), while providing USD trillions in revenue from cheap clean energy sales (@1-3¢/kWh) to amortize the scheme. Total system efficiency compares favorably to automobiles; total system power density is comparable to nuclear power. This approach- self-funding, pay-as-you-go, minimally intrusive, scalable, complementary with a portfolio of other measures and above all reversible-is not precluded by international treaty. Indeed geoengineering may be the best killer app to bootstrap orbital industry and humanity ad astra, because the terawattscale product is comparable to the power required for interstellar travel. If Tellurian spacefaring civilization bootstraps its exponential growth with multi-terawatt maser beams from such lightsails, there might eventually be enough of them to have a detectable effect on Sol's apparent luminosity at certain wavelengths, as seen from far away, similar to the eponymous Dyson Sphere, hence the moniker.
... Here, we use an atmosphere-ocean chemistry-climate model to study atmospheric composition changes for one of the most common geoengineering modelling experiments: the reflection of solar energy before it can enter the Earth's atmosphere, an idea often depicted by the use of space mirrors (Early, 1989;Seifritz, 1989). This idealized geoengineering experiment belongs to methods subsumed under the term solar radiation management (SRM). ...
... In the G1 experiment the effect of an abrupt quadrupling of atmospheric carbon dioxide (CO 2 ) on the global mean surface temperature is approximately offset by reducing the model's solar constant. This can be thought of as an experiment in which space-mirrors reflect sunlight before it enters the Earth's atmosphere (Early, 1989;Seifritz, 1989). Starting from approximately pre-industrial concentrations with atmospheric CO 2 at ∼ 285 ppmv (piControl), we thus carried out, firstly, an abrupt 4 × CO 2 experiment, in which atmospheric CO 2 is instantaneously quadrupled to ∼ 1140 ppmv and, secondly, a G1 type experiment in which the global warming caused by 4 × CO 2 was offset by a solar irradiance reduction of 49.0 Wm −2 (∼ 3.6 %). ...
Article
Full-text available
Various forms of geoengineering have been proposed to counter anthropogenic climate change. Methods which aim to modify the Earth's energy balance by reducing insolation are often subsumed under the term Solar Radiation Management (SRM). Here, we present results of a standard SRM modelling experiment in which the incoming solar irradiance is reduced to offset the global mean warming induced by a quadrupling of atmospheric carbon dioxide. For the first time in an atmosphere–ocean coupled climate model, we include atmospheric composition feedbacks such as ozone changes under this scenario. Including the composition changes, we find large reductions in surface UV-B irradiance, with implications for vitamin D production, and increases in surface ozone concentrations, both of which could be important for human health. We highlight that both tropospheric and stratospheric ozone changes should be considered in the assessment of any SRM scheme, due to their important roles in regulating UV exposure and air quality.
... Typically, these proposals require deploying the occulting structure close to the L 1 Lagrange equilibrium point on the Sun-Earth line, as shown in Fig 1, some 1.5x10 6 km sunward of the Earth. The estimated mass of the deployed structure is in the order of 10 7 -10 8 tonnes [9][10][11][12]. While this is clearly a vast space-based endeavour, its mass is already at the same engineering scale as terrestrial civil engineering projects (e.g., the Chinese Three Gorges Dam). ...
... Previous work in astronautics [9][10][11][12] has already discussed the feasibility of implementing the sunshade concept to counteract the increase of global mean temperature. On the other hand, the potential for spatio-temporal shading patterns to regionally suppress anthropogenic climate variability has also been demonstrated using fully-coupled atmosphere-ocean general circulation models [19,21]. ...
Article
Full-text available
Within the context of anthropogenic climate change, but also considering the Earth’s natural climate variability, this paper explores the speculative possibility of large-scale active control of the Earth’s radiative forcing. In particular, the paper revisits the concept of deploying a large sunshade or occulting disk at a static position near the Sun-Earth L1 Lagrange equilibrium point. Among the solar radiation management methods that have been proposed thus far, space-based concepts are generally seen as the least timely, albeit also as one of the most efficient. Large occulting structures could potentially offset all of the global mean temperature increase due to greenhouse gas emissions. This paper investigates optimal configurations of orbiting occulting disks that not only offset a global temperature increase, but also mitigate regional differences such as latitudinal and seasonal difference of monthly mean temperature. A globally resolved energy balance model is used to provide insights into the coupling between the motion of the occulting disks and the Earth’s climate. This allows us to revise previous studies, but also, for the first time, to search for families of orbits that improve the efficiency of occulting disks at offsetting climate change on both global and regional scales. Although natural orbits exist near the L1 equilibrium point, their period does not match that required for geoengineering purposes, thus forced orbits were designed that require small changes to the disk attitude in order to control its motion. Finally, configurations of two occulting disks are presented which provide the same shading area as previously published studies, but achieve reductions of residual latitudinal and seasonal temperature changes.
... The most direct geoengineering strategy is to reduce the amount of incoming sunlight reaching the surface, which is referred to as "solar radiation management" or SRM (Caldeira, Bala, & Cao, 2013). 1 One of the widely discussed methods for SRM is the injection of reflective particles into the stratosphere (Crutzen, 2006;Wigley, 2006;Matthews & Caldeira, 2007;Rasch et al., 2008;Brovkin et al., 2009;Keith, 2010;Pidgeon, Parkhill, Corner, & Vaughan, 2013) because it provides a "fast, cheap, and easy" (Caldeira, 2015) way to cool the planet. A similar effect could be achieved by deploying an orbiting solar shield to reflect away a portion of sunlight from space (Early, 1989;Angel, 2006), although this option is orders of magnitude more expensive than aerosol injection. Cloud seeding to enhance the reflectivity of marine stratocumulus clouds is another SRM option that can provide significant cooling to particular regions (Jones, Haywood, & Boucher, 2009;Rasch, Latham, & Chen, 2009;Korhonen, Carslaw, & Romakkaniemi, 2010). ...
... However, intentional SRM geoengineering could be used to create strong global cooling that persists for thousands of years and damps out any variations from ice-age cycles. Aerosol SRM geoengineering is likely the cheapest option to enlarge the ice caps (Keith, 2010;Caldeira et al., 2013), but a space-based solar shield (Early, 1989;Angel, 2006) could also provide the needed long-term cooling. Either of these SRM solutions, or a combination of the two, could also be complemented with cloud seeding (Jones et al., 2009;Rasch et al., 2009;Korhonen et al., 2010) and other SRM strategies (Lenton & Vaughan, 2009) in order to optimize the growth of the polar ice caps. ...
Article
The climate of Earth is susceptible to catastrophes that could threaten the longevity of human civilization. Geoengineering to reduce incoming solar radiation has been suggested as a way to mediate the warming effects of contemporary climate change, but a geoengineering program for thousands of years could also be used to enlarge the size of the polar ice caps and create a permanently cooler climate. Such a large ice cap state would make Earth less susceptible to climate threats and could allow human civilization to survive further into the future than otherwise possible. Intentionally extending Earth's glacial coverage will require uninterrupted commitment to this program for millenia but would ultimately reach a cooler equilibrium state where geoengineering is no longer needed. Whether or not this program is ever attempted, this concept illustrates the need to identify preference among potential climate states to ensure the long-term success of civilization.
... Then, in 1989, Early proposed using a "solar shield" to protect Earth from global warming. However, he cautioned that the scale and enormous costs (around $1-10 trillion) would be a seriously limiting factor (Early, 1989 Whilst no strategy or plan is currently in place (Hogenboom, 2013), scientific reports have increasingly concluded that sunshades are worth studying despite doubts over their affordability and may be inevitable in a worst case scenario (Lunt, 2012). ... ... The following solutions in Table 3.2 have been suggested as means to achieve this: Bala, 2014;Early, 1989;Angel, 2006). ... Thesis With attempts at tackling anthropogenic climate change failing, attention is now turning to space-based technology as a solution; specifically solar power satellites (SPSs) for generating a renewable form of energy and the geoengineering concept of space sunshades to directly neutralise climate change. With many countries researching the possibility of utilising SPSs as their future energy direction and the IPCC exploring the possibility of deploying geoengineering schemes within their fifth assessment report (2014), pressure is growing for the utilisation of both of these technologies. However with neither currently in deployment, most research to date has been regarding the technological efficiencies of the concepts rather than the wider implications they entail. The aim of this research was to impartially assess the viability of space-based technology in combatting climate change and producing renewable energy, using case studies which focus on the use of SPSs and sunshades. The data was gathered by a mixed method approach. This analysed literature reviews, primary and supplementary semi-structured interviews with experts, data requests and the findings of a climate model in relation to objectives under the aim of this research. The findings of this analysis suggest that SPSs would provide upwards of 335% more power on average than ground-based photovoltaics with the same conversion efficiency. However, it also found that there has been no LCAs or public perception data gathered on SPS deployment. In terms of sunshades, the research highlighted that although the technology could return average global surface temperatures back to acceptable levels, regional variations will occur. Nevertheless, it also showed that despite the associated high costs of sunshades, they could be over 10 times cheaper to deploy than to combat climate change directly. Discussion was then given to put these findings into an appropriate context before recommendations were made to the space industry and for further research in order to enhance and elaborate on the findings of this research. ... Similarly, the reduction of incoming solar radiation was considered by placing a deflector of 1400-km diameter at the first Lagrange Point, manufactured and launched from the Moon [33]. The idea to mine the moon [28] to create a shielding cloud of dust is in the same league. ... Article Full-text available The best way to reduce global warming is, without any doubt, cutting down our anthropogenic emissions of greenhouse gases. But the world economy is addict to energy, which is mainly produced by fossil carbon fuels. As economic growth and increasing world population require more and more energy, we cannot stop using fossil fuels quickly, nor in a short term. On the one hand, replacing this addiction with carbon dioxide-free renewable energies, and energy efficiency will be long, expensive and difficult. On the other hand, meanwhile effective solutions are developed (i.e. fusion energy), global warming can be alleviated by other methods. Some geoengineering schemes propose solar radiation management technologies that modify terrestrial albedo or reflect incoming shortwave solar radiation back to space. In this paper we analyze the physical and technical potential of several disrupting technologies that could combat climate change by enhancing outgoing longwave radiation and cooling down the Earth. The technologies proposed are power-generating systems that are able to transfer heat from the Earth surface to the upper layers of the troposphere and then to the space. The economical potential of some of these technologies is analyzed as they can at the same time produce renewable energy, thus reduce and prevent future greenhouse gases emissions, and also present a better societal acceptance comparatively to geoengineering. ... A few approaches have been proposed to reflect more sunlight back to space via placing certain types of reflectors (a large mirror, trillions of small spacecraft, and a large ring of space dust) in space (Early, 1989;Angel, 2006;Pearson et al., 2006). The reflectors can be placed near the first Lagrange point (L1) of the EartheSun system (L1 is a neutrally stable point on the axis between Earth and the Sun where the forces pulling an object toward the Sun are exactly balanced by the forces pulling an object toward the Earth). ... Article Full-text available Geoengineering (also called climate engineering), which refers to large-scale intervention in the Earth's climate system to counteract greenhouse gas-induced warming, has been one of the most rapidly growing areas of climate research as a potential option for tackling global warming. Here, we provide an overview of the scientific background and research progress of proposed geoengineering schemes. Geoengineering can be broadly divided into two categories: solar geoengineering (also called solar radiation management, or SRM), which aims to reflect more sunlight to space, and carbon dioxide removal (CDR), which aims to reduce the CO2 content in the atmosphere. First, we review different proposed geoengineering methods involved in the solar radiation management and carbon dioxide removal schemes. Then, we discuss the fundamental science underlying the climate response to the carbon dioxide removal and solar radiation management schemes. We focus on two basic issues: 1) climate response to the reduction in solar irradiance and 2) climate response to the reduction in atmospheric CO2. Next, we introduce an ongoing geoengineering research project in China that is supported by National Key Basic Research Program. This research project, being the first coordinated geoengineering research program in China, will systematically investigate the physical mechanisms, climate impacts, and risk and governance of a few targeted geoengineering schemes. It is expected that this research program will help us gain a deep understanding of the physical science underlying geoengineering schemes and the impacts of geoengineering on global climate, in particular, on the Asia monsoon region. ... Similarly, the reduction of incoming solar radiation was considered by placing a deflector of 1400-km diameter at the first Lagrange Point, manufactured and launched from the Moon [33]. The idea to mine the moon [28] to create a shielding cloud of dust is in the same league. ... Article Full-text available Over the last decades, fighting global warming has become the most important challenge humanity has to face. Therefore technologies of carbon dioxide capture, sequestration and recycling are equally important in order to tackle the global climate change stakes. Among recycling technologies, photocatalytic processes reducing CO 2 with H 2 O back to fuels or to other useful organic compounds, have the potential to be part of a renewable energy system. Indeed these processes can help to control CO 2 emissions and eventually eliminate CO 2 in excess. This perspective paper describes a large size device, able simultaneously: to proceed to direct air capture (DAC) of CO 2 ; to transform part of it into useful chemicals, like hydrocarbons or syngas; and to produce renewable energy, thus preventing future CO 2 emissions. Synergies between solar chimney power plants (SCPPs) and semiconductor photocatalysis in order to create giant photocatalytic reactors for artificial photosynthesis are discussed, as well as scale economies for unconventional carbon capture directly from the atmosphere. This paper presents a carbon negative emission technology obtained by coupling SCPPs with DAC systems which allows many scale economies, and also synergies to proceed to solar-to-chemical energy-conversion process by photocatalytic reduction of atmospheric CO 2 under sunlight. ... As can be seen in Table 2, the use of unstable displaced orbits could reduce the mass requirements and the size of the reector. Note that a mirror diameter of order 500 − 700 km would envisage many smaller reectors distributed about the same orbit (Early, 1989;Angel, 2006;Pearson et al., 2006). ... Article Several space-based climate engineering methods, including shading the Earth with a particle ring for active cooling, or the use of orbital reflectors to increase the total insolation of Mars for climate warming have been considered to modify planetary climates in a controller manner. In this study, solar reflectors on polar orbits are proposed to intervene in the Earth's climate system, involving near circular polar orbits normal to the ecliptic plane of the Earth. Similarly, a family of displaced polar orbits (non-Keplerian orbits) are also characterized to mitigate future natural climate variability, producing a modest global temperature increase, again to compensate for possible future cooling. These include deposition of aerosols in the stratosphere from large volcanic events. The two-body problem is considered, taking into account the effects of solar radiation pressure and the Earth's . J2 oblateness perturbation. ... A number of studies have suggested reducing the amount of sunlight reaching the Earth by placing solid or refractive disks, or dust particles, in outer space (Early, 1989;Mautner, 1991;Angel, 2006;Bewick et al., 2012). Although we do not assess the feasibility of these methods, they provide an easily described mechanism for reducing sunlight reaching the planet, and motivate the idealized studies discussed in Section 7.7.3. ... Chapter Full-text available ... Terraforming by climatic adjustment relies on inserting greenhouse gases [13] or scattering aerosols [14] into the atmosphere of a planet, or placing mirrors or material into the planet's orbit [15] so as to concentrate or block incoming starlight (sunlight). Such attacks are most likely to be effective if the planet is at the edge of the star's habitable zone. ... Article Full-text available Science fiction offers scenarios in which a planet is destroyed in combat. However, these are often impractical. Instead of supplying all the energy required, more plausible attacks may use leverage in order to damage or destroy the planet or its biosphere. In order to study the conduct, observation, or defence associated with such attacks, a range of potentially practical weapon and defence technologies are discussed. These are: altering the radiation budget of a planet so as to substantially change its temperature; introducing invasive species to transform the biogeochemistry; and using orbital perturbations of comets and asteroids to cause collisions, or to move the planet to an unstable or uninhabitable orbit. Weapon transit and effect times associated with these technologies render them suitable only for extreme slow-motion warfare, assuming near-term technologies. ... In the first approach, the amount of solar absorption by the planet is reduced by artificially enhancing the planetary albedo so that the reduced insolation compensates the radiative forcing due to rising GHGs. Some proposed methods are injecting sulfate aerosols in the stratosphere (Budkyo, 1982;Crutzen, 2006;Wigley, 2006) and placing space-based sun shields in between the Sun and the Earth (Early, 1989). Other SRM methods include marine cloud brightening and enhancement of land/ocean surface albedo. ... Article Full-text available Solar radiation management (SRM) geoengineering has been proposed as a potential option to counteract climate change. We perform a set of idealized geoengineering simulations using Community Atmosphere Model version 3.1 developed at the National Center for Atmospheric Research to investigate the global hydrological implications of varying the latitudinal distribution of solar insolation reduction in SRM methods. To reduce the solar insolation we have prescribed sulfate aerosols in the stratosphere. The radiative forcing in the geoengineering simulations is the net forcing from a doubling of CO2 and the prescribed stratospheric aerosols. We find that for a fixed total mass of sulfate aerosols (12.6 Mt of SO4), relative to a uniform distribution which nearly offsets changes in global mean temperature from a doubling of CO2, global mean radiative forcing is larger when aerosol concentration is maximum at the poles leading to a warmer global mean climate and consequently an intensified hydrological cycle. Opposite changes are simulated when aerosol concentration is maximized in the tropics. We obtain a range of 1K in global mean temperature and 3% in precipitation changes by varying the distribution pattern in our simulations: this range is about 50% of the climate change from a doubling of CO2. Hence, our study demonstrates that a range of global mean climate states, determined by the global mean radiative forcing, are possible for a fixed total amount of aerosols but with differing latitudinal distribution. However, it is important to note that this is an idealized study and thus not all important realistic climate processes are modeled. ... Such an object would be placed at the Sun-Earth L 1 Lagrange point. It appears that James Early was one of the first to suggest such a proposal [129], which involved a 2000km, 10 micron think glass shield made of Moon rock which would reduce solar insolation by about 2%. At about the same time Seifritz also suggested a similar scheme [130], although his shield would be made of aluminum and would compensate for a temperature increase of 2.5K on Earth with a disc approximately 2400km in diameter. ... Article Full-text available A survey of highly non-Keplerian orbits with low-thrust propulsion is presented. Keplerian orbits neglect atmospheric drag, solar radiation pressure, nonspherical central bodies, and other perturbations. The term non-Keplerian has been used in reference to orbits where a perturbing or propulsive acceleration acts in addition to that of the effects of gravity. Highly-non-Keplerian orbits can be obtained by considering the dynamics of a low-thrust spacecraft in a rotating frame of reference, where the angular velocity of rotation of the frame of reference is used as a free parameter of the problem. Stationary solutions to the equations of motion can then be sought in this rotating frame of reference, which correspond to periodic, displaced orbits when viewed from an inertial frame of reference. The more thrust that an ion engine can generate, the greater the gravity gradient that can be compensated for and hence the more opportunities there are for applying non-Keplerian orbits. ... In 1989, James Early published an analysis suggesting that sunlight could be deflected away from the Earth with satellites placed between Earth and the sun [Early, 1989]. In 1992, solar geoengineering was highlighted in a 1992 report by the US National Research Council [[National Research Council, 1992]. ... Article Full-text available Earth's Future invited “leading experts in the field of geoengineering research to contribute brief reflections (2–5 pages) on the development of the discussion over the past decade and to consider where it may be going in the next 10 years.” Responding to this request, we offer the following text in the spirit of reflections that emphasize our personal roles and viewpoints. The primary focus of many of our comments is solar geoengineering and not carbon dioxide removal (CDR). Thus, this text is not intended to comprise a comprehensive review or set of carefully documented analyses. Our primary conclusion is that sustained progress in “geoengineering” research will depend on social and material support for experimental work that can provide the observational basis for improved modeling and analysis, and, potentially, development and deployment of systems that may help protect the environment and improve human well-being. Relevant issues, and potential future trajectories, for CDR technologies may differ dramatically from those for solar geoengineering technologies. ... Terrestrial geo-engineering is currently being explored as a largescale venture to mitigate against rapid terrestrial climate change due to anthropogenic carbon emissions. A range of schemes have been proposed, including the use of orbiting solar reflectors to reduce solar insolation to compensate for increased radiative forcing of the climate (Early 1989;Angel 2006). While the scale of endeavour required to deploy geo-engineering schemes is impressive, on an even more ambitious scale the same technologies which can be envisaged to engineer the Earth's climate can be scaled to engineer the climate of Mars. ... Article Terrestrial geo-engineering is currently being explored as a large-scale venture to mitigate against rapid terrestrial climate change due to anthropogenic carbon emissions. A range of schemes have been proposed, including the use of orbiting solar reflectors to reduce solar insolation to compensate for increased radiative forcing of the climate (Early 1989; Angel 2006). While the scale of endeavour required to deploy geo-engineering schemes is impressive, on an even more ambitious scale the same technologies which can be envisaged to engineer the Earth’s climate can be scaled to engineer the climate of Mars. Such terraforming schemes (engineering an Earth-like climate) have long been discussed, although the concept became somewhat more mainstream with the work of Sagan and others (Sagan 1961, 1973). Bioengineering schemes have been proposed, including the delivery of customized organisms to convert carbon dioxide to oxygen in the atmosphere of Mars, and darkening the Martian polar caps to reduce their albedo, again using customized organisms. Halocarbons synthesised on Mars have also been considered as a tool to quickly raise the surface temperature and so liberate trapped carbon dioxide (Gerstell et al. 2001; Badescu 2005). For other details see Chap. 26. ... There has been a number of proposals for managing solar radiation, or Solar Radiation Management (SRM). Two space-based approaches have been proposed; the deployment of space deflectors at the Lagrange 1 gravitational saddle point between the sun and the earth (Early 1989), or a ring of near-earth space mirrors (Wood 2012). ... Article Full-text available The long-term solution to global climate warming is the necessary transition from a primarily fossil fuel economy to renewable energy sources. Recent IPCC (Intergovernmental Panel on Climate Change) Special Report emphasizes the need to limit global temperature increase relative to pre-industrial level to 1.5 o C. A previous target had been a limit of 2 o C rise via the IPCC RCP (Representative Concentration Pathway) 2.6. The more stringent target of 1.5 o C requires reduction of Green House Gas(GHG) emissions to near zero around mid-century. Failure to limit temperature rise may result in positive feedback such as ice shelf melting a factor affecting global albedo that could further accelerate warming. There are tools available to climate management that can be implemented to mitigate such potential runaway scenario. We propose here a solar radiation reduction approach that can be easily deployed and recalled. The basic concept is the deployment of floating mirrors near the equatorial international waters. We describe the design of such mirrors and features that would confine the mirror positions within a narrow band of the equatorial region. An example for an ~1 o C reduction is described. ... injection of scattering aerosols into the stratosphere [Budyko, 1977], deployment of an array of mirrors in space [Early, 1989], seeding marine stratocumulus clouds [Latham, 1990], and increasing the albedo of ocean [Seitz, 2011] or land surface [Gaskill, 2004]. In contrast to these solar geoengineering schemes that seek to modify shortwave radiation fluxes, Mitchell and Finnegan [2009] proposed a form of radiation management that seeks to modify longwave radiation. ... Article Solar geoengineering has been proposed as a backup plan to offset some aspects of anthropogenic climate change if timely CO2 emission reductions fail to materialize. Modeling studies have shown that there are trade-offs between changes in temperature and hydrological cycle in response to solar geoengineering. Here we investigate the possibility of stabilizing both global mean temperature and precipitation simultaneously by combining two geoengineering approaches: stratospheric sulfate aerosol increase (SAI) that deflects sunlight to space and cirrus cloud thinning (CCT) that enables more longwave radiation to escape to space. Using the slab ocean configuration of National Center for Atmospheric Research Community Earth System Model, we simulate SAI by uniformly adding sulfate aerosol in the upper stratosphere and CCT by uniformly increasing cirrus cloud ice particle falling speed. Under an idealized warming scenario of abrupt quadrupling of atmospheric CO2, we show that by combining appropriate amounts of SAI and CCT geoengineering, global mean (or land mean) temperature and precipitation can be restored simultaneously to preindustrial levels. However, compared to SAI, cocktail geoengineering by mixing SAI and CCT does not markedly improve the overall similarity between geoengineered climate and preindustrial climate on regional scales. Some optimal spatially nonuniform mixture of SAI with CCT might have the potential to better mitigate climate change at both the global and regional scales. ... Another widely proposed method is marine cloud brightening that involves spraying droplets of seawater into the marine boundary layer to increase cloud condensation nuclei, making low-level clouds more reflective [10,11]. Other proposed methods of solar geoengineering involve deploying space mirrors [12], increasing albedo of land [13] and ocean surface [14]. Another type of proposed radiation management method is cirrus cloud thinning, which aims to cool the Earth by reducing cirrus cloud coverage and optical thickness to allow more long-wave radiation to escape to space [15]. ... Article Full-text available Purpose of Review Review existing studies on the carbon cycle impact of different solar geoengineering schemes. Recent Findings The effect of solar geoengineering on terrestrial primary productivity is typically much smaller than that of CO2 fertilization. Changes in the partitioning between direct and diffuse radiation in response to stratospheric aerosol injection could substantially alter modeled plant productivity. Inclusion of the nitrogen cycle would further modify the terrestrial response to solar geoengineering. Relative to a high-CO2 world, solar geoengineering, via cooling the surface ocean, would increase CO2 solubility, enhancing oceanic CO2 uptake. However, the effect from geoengineering-induced changes in ocean circulation and marine biology would be more complicated. Solar geoengineering would have a small effect on surface ocean acidification, but could accelerate acidification in the deep ocean. Solar geoengineering would reduce atmospheric CO2, but the relative contribution from the ocean sink and land sink is uncertain. Summary To date, there are only a few studies on the carbon cycle response to solar geoengineering. Coordinated geoengineering model intercomparison studies are needed to gain a better understanding of the carbon cycle impact of solar geoengineering and feedback on climate change. ... Similarly, the reduction of incoming solar radiation was considered by placing a deflector of 1400-km diameter at the first Lagrange Point, manufactured and launched from the Moon [33]. The idea to mine the moon [28] to create a shielding cloud of dust is in the same league. ... Article Geoengineering schemes propose solar radiation management technologies that modify terrestrial albedo or reflect incoming shortwave solar radiation back to space. Instead we propose "earth radiation management" and to enhance outgoing longwave radiation http://www.sciencedirect.com/science/article/pii/S1364032113008460 to fight global warming. In this paper we analyze the physical and technical potential of several disrupting technologies that could combat climate change by enhancing outgoing longwave radiation and cooling down the Earth. The technologies proposed are power-generating systems that are able to transfer heat from the Earth surface to the upper layers of the troposphere and then to the space. The economical potential of some of these technologies is analyzed as they can at the same time produce renewable energy, thus reduce and prevent future greenhouse gases emissions, and also present a better societal acceptance comparatively to geoengineering. ... Prior proposals to counter global warming [6] have included 6 approaches. These are to place reflectors or bubbles in Space [7][8][9] to reflect part of solar irradiance; chimneys ingesting air, removing GHG and ejecting purified air; aerosol clouds released over Antarctica . [10,11] to slow down summer melting [12] of the ice cap; reflective balloons released into the sky; reflective particles released along with industrial exhaust [13] (or aluminum nanoparticles in airline engine exhaust per some rumors of illegal Climate Engineering) and wind turbines pumping Antarctic sea-water onto the ice cap. ... ... Planetary absorption of solar radiation can be reduced either by deflecting solar radiation in space, in the atmosphere or at the surface. Reflectors in L1 Lagrange point and mirrors in low earth orbit are some examples for space based techniques (Angel 2006;Early 1989;NAS 1992;Seifritz 1989). Artificial injection of aerosols in the stratosphere (Crutzen 2006;Robock et al. 2009Robock et al. , 2008 and enhancement of albedo of marine clouds (Bower et al. 2006;Latham 1990Latham , 2002Latham et al. 2008) are proposed SRM schemes for reflecting solar radiation in the atmosphere. ... Article Full-text available A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO2 leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (−8.2 W m−2) to counter global mean radiative forcing from a doubling of CO2 (3.3 W m−2) is approximately twice the forcing needed over the oceans (−4.2 W m−2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification. ... Many different geoengineering schemes have been proposed (Keith 2000), though each has certain limitations.  Placing shades, mirrors, or other reflecting bodies into orbit between Earth and the Sun ( " space reflectors " ; Angel 2006; Early 1989) shares some of SAI's advantages and is also not prone to intermittency, but would be very expensive and may not even be feasible with available technology. Because it does not share these limitations, SAI has emerged as the most promising geoengineering scheme. ... Article Full-text available Perceived failure to reduce greenhouse gas emissions has prompted interest in avoiding the harms of climate change via geoengineering, that is, the intentional manipulation of Earth system processes. Perhaps the most promising geoengineering technique is stratospheric aerosol injection (SAI), which reflects incoming solar radiation, thereby lowering surface temperatures. This paper analyzes a scenario in which SAI brings great harm on its own. The scenario is based on the issue of SAI intermittency, in which aerosol injection is halted, sending temperatures rapidly back toward where they would have been without SAI. The rapid temperature increase could be quite damaging, which in turn creates a strong incentive to avoid intermittency. In the scenario, a catastrophic societal collapse eliminates society’s ability to continue SAI, despite the incentive. The collapse could be caused by a pandemic, nuclear war, or other global catastrophe. The ensuing intermittency hits a population that is already vulnerable from the initial collapse, making for a double catastrophe. While the outcomes of the double catastrophe are difficult to predict, plausible worst-case scenarios include human extinction. The decision to implement SAI is found to depend on whether global catastrophe is more likely from double catastrophe or from climate change alone. The SAI double catastrophe scenario also strengthens arguments for greenhouse gas emissions reductions and against SAI, as well as for building communities that could be self-sufficient during global catastrophes. Finally, the paper demonstrates the value of integrative, systems-based global catastrophic risk analysis. ... For example, McInnes (2002) showed that the required reflector area to increase the total insolation of Mars by 30%, as part of a large-scale terraforming effort, is of the order 10 13 m 2 (and mass of the order 10 10 kg). This size implies that a large space mirror would be replaced by a large number of smaller reflectors distributed about the orbit (Early 1989;Angel 2006;Pearson et al. 2006). Similarly, , , Salazar et al. (2017) proposed intervening in Earth's climate system through spacebased solar reflectors placed in non-Keplerian orbits. ... ... Planetary engineering is the application of technology for the purpose of influencing the global properties of a planet, while geoengineering is planetary engineering applied specifically to Earth, by affecting the greenhouse effect, atmospheric composition, solar insolation, or impact flux (Sagan 1973 On the other hand, paraterraforming is engineering that involves the construction of a large-scale habitable enclosure, like the Biosphere 2 experiment here on Earth, a closed-ecosystem environment in a dome-structure (Taylor 1992). Some proposed terraforming methods include creating orbital mirrors ( Figure 2 on the next page) that will reflect sunlight and heat the desired planet's surface, greenhouse gasproducing factories to trap solar radiation, and importing volatiles through asteroid or comet impacts to create volatile release (Early 1989;Zubrin and McKay 1997;Clacey et al. 2005). Other viable technologies suggested by the aforementioned authors include artificial super greenhouse gasses, albedo reduction, and biological seeding. ... Technical Report Full-text available This investigation into chemically altering, and thus geologically changing the nature of a planetary atmosphere and its surface provides new scientific predictions, insight, and numerical theories into the feasibility of technologically inducing the habitability of other worlds. Innumerable permutations of potential planetary evolution pathways exist due to large variations in the astrophysical, atmospheric, and geologic properties of a given world, dictated by unique planetary formation, dynamics, and evolution. Surface interactions that give rise to habitable climates are driven by geochemical reactions and geomorphic processes that can act in feedbacks to either promote or decay the climactic habitability of a planetary atmosphere and surface. Using the TerraGenesis smartphone application created by Alexander Winn, I simulate and track 21 different technologically induced planetary engineering scenarios. I present numerical-game simulation modeling of our solar system’s real terrestrial bodies: Mercury, Venus, Earth, the Moon, and Mars, Jupiter’s moons: Io, Europa, Ganymede, Callisto, Saturn’s moons: Tethys, Dione, Rhea, Titan, and Iapetus, Uranus’s moon Oberon, and Pluto. I test a range of four hypothetical exoplanets to colonize: Bacchus, Pontus, Ragnarok, and Boreas. I also use the model on the exoplanet TRAPPIST-1d, while considering this approach for other future exoplanet studies. Calculations in this application are taken out with simple, coupled numerical rules, with model years into C.E., the Common Era. The user of this application 'controls' the terraformation process by manipulating the temperature, atmospheric pressure, oxygen content, sea level, and biomass, limited by economic resources and population. Technologically induced terraforming in this numerical model produced all 21 tested habitable worlds, and reached stability within 1,000–3,000 mission years. Through testing the efficacy of terraforming technologies to combat modern climate change on the Earth, this report additionally shows that it is at least feasible to achieve stable habitability on Earth before (or after) a global climate catastrophe; reversing the effects of modern climate change may take on the order of 100–1,000 years. This paper also reviews and condenses the current literature in the year 2018 on terraforming as well as recent developments and advancements. This is the complete report and in this state has not been submitted for review. ... This can be prevented if the planet has some means of limiting the sunlight reaching the planet. One reasonably-feasible solution might be a space-based megastructure, such as an orbital sunshade, which has been proposed for climate engineering on Earth (Early 1989;Angel 2006). This megastructure could take the form of a large swarm of smaller sunshades which orbit the barycenter at various inclinations and semimajor axes to shield the planet throughout the period of greatest danger, or they could orbit the planet and re-orient themselves to let sunlight through during excursions away from the plane. ... Preprint Full-text available Many previous authors have attempted to find explanations for Westeros's climate, characterized by a generally moderate, Earth-like climate punctuated by extremely long and cold winters, separated by thousands of years. One explanation that has been proposed is that the planet orbits in a Sitnikov configuration, where two equal-mass stars (or a star and a black hole) orbit each other on slightly eccentric orbits, and the planet moves along a line through the barycenter perpendicular to the primaries' orbital plane (Freistetter & Gr\"utzbauch 2018). We modify an intermediate-complexity GCM to include the effects of such an orbit and integrate it for thousands of years to determine whether such an orbit can a) be habitable and b) explain the climatic variations observed by the inhabitants of Westeros, in both double-star and star-black hole configurations. While configurations with low primary eccentricity and initial conditions that permit only small excursions from the ecliptic plane are habitable, these orbits are too stable to explain Westerosi climate. We find that while orbits with more bounded chaos are able to produce rare anomalously long and cold winters similar to Westeros's Long Night, huge variations in incident stellar flux on normal orbital timescales should render these planets uninhabitable. We note that the presence of an orbital megastructure, either around the planet or the barycenter, could block some of the sunlight during crossings of the primaries' orbital plane and preserve Westeros's habitability. While we find that bounded chaotic Sitnikov orbits are a viable explanation for Westeros's Long Night, we propose that chaotic variations of the planet's axial tilt or semimajor axis, potentially due to torques from nearby planets or stars, may be a more realistic explanation than Sitnikov orbits. ... For example, McInnes (2002) showed that the required reflector area to increase the total insolation of Mars by 30%, as part of a large-scale terraforming effort, is of the order 10 13 m 2 (and mass of the order 10 10 kg). This size implies that a large space mirror would be replaced by a large number of smaller reflectors distributed about the orbit (Early 1989;Angel 2006;Pearson et al. 2006). Similarly, , , Salazar et al. (2017) proposed intervening in Earth's climate system through spacebased solar reflectors placed in non-Keplerian orbits. ... Article Full-text available Although the Martian environment is very cold (averaging about −60∘ C), highly oxidizing and desiccated, several studies have proposed human colonization of Mars. To carry out this ambitious goal, terraforming schemes have been designed to warm Mars and implant Earth-like life. Mars climate engineering includes the use of orbiting solar reflectors to increase the total solar insolation. In this study, Sun-synchronous solar reflectors orbits with inclination equal or less than 90∘ with respect to the orbital plane of Mars are considered to intervene with the Mars’ climate system. With different inclinations, a family of Sun-synchronous solar reflectors orbits distributes azimuthally the energy intercepted by the reflector. The two-body problem is considered, and the Gauss’s form of the variational equations is used to find the conditions to achieve a Sun-synchronous frozen orbit with inclination equal or less than 90∘, taking into account the effects of solar radiation pressure for a perfectly reflecting space mirror and Mars’ J2 oblateness perturbation. ... Solar geoengineering, also called solar radiation modification, has been proposed as a potential way to counteract some aspects of changes induced by anthropogenic global warming (National Research Council, 2015). Proposed solar geoengineering approaches aim to cool the Earth by deflecting sunlight back to space via approaches such as placing small mirrors in space (Early, 1989), injecting sulfate aerosols into the stratosphere (Budyko, 1982), enhancing the marine cloud reflectivity (Latham et al., 2008), and modifying surface albedo (Seitz, 2011). In addition to solar radiation modification, Mitchell and Finnegan (2009) proposed to reduce the amount of cirrus cloud cover. ... Article Full-text available A number of radiation modification approaches have been proposed to counteract anthropogenic warming by intentionally altering Earth's shortwave or longwave fluxes. While several previous studies have examined the climate effect of different radiation modification approaches, only a few have investigated the carbon cycle response. Our study examines the response of plant carbon uptake to four radiation modification approaches that are used to offset the global mean warming caused by a doubling of atmospheric CO2. Using the National Center for Atmospheric Research Community Earth System Model, we performed simulations that represent four idealized radiation modification options: solar constant reduction, sulfate aerosol increase (SAI), marine cloud brightening, and cirrus cloud thinning (CCT). Relative to the high CO2 state, all these approaches reduce gross primary production (GPP) and net primary production (NPP). In high latitudes, decrease in GPP is mainly due to the reduced plant growing season length, and in low latitudes, decrease in GPP is mainly caused by the enhanced nitrogen limitation due to surface cooling. The simulated GPP for sunlit leaves decreases for all approaches. Decrease in sunlit GPP is the largest for SAI which substantially decreases direct sunlight, and the smallest for CCT, which increases direct sunlight that reaches the land surface. GPP for shaded leaves increases in SAI associated with a substantial increase in surface diffuse sunlight, and decreases in all other cases. The combined effects of CO2 increase and radiation modification result in increases in primary production, indicating the dominant role of the CO2 fertilization effect on plant carbon uptake. ... Geoengineering is considered to be a backup approach to slow down or mitigate global and Arctic warming (National Research Council 2015). Many methods have been proposed in the geoengineering schemes, such as stratospheric aerosol injections (SAI), marine stratocumulus clouds, and increasing the surface albedo (Kravitz et al. 2011;Early 1989;Seitz 2011;Cao et al. 2017). Among these approaches, the injection of stratospheric aerosols seems to be an effective way to slow down future warming (Lenton and Vaughan, 2009), which is partly based on the knowledge of the volcanic impact on global climate (Crutzen 2006;Plazzotta et al. 2018). ... Article Full-text available Stratospheric aerosol injection (SAI) is considered as a backup approach to mitigate global warming, and understanding its climate impact is of great societal concern. It remains unclear how differently global monsoon (GM) precipitation would change in response to tropical and Arctic SAI. Using the Community Earth System Model, a control experiment and a suite of 140-year experiments with CO2 increasing by 1% per year (1% CO2) are conducted, including ten tropical SAI and ten Arctic SAI experiments with different injecting intensity ranging from 10 to 100 Tg yr−1. For the same amount of injection, a larger reduction in global temperature occurs under tropical SAI compared with Arctic SAI. The simulated result in the last 40 years shows that, for a 10 Tg yr−1 injection, GM precipitation decreases by 1.1% (relative to the 1% CO2 experiment) under Arctic SAI, which is weaker than under tropical SAI (1.9%). Further, tropical SAI suppresses precipitation globally, but Arctic SAI reduces the Northern Hemisphere monsoon (NHM) precipitation by 2.3% and increases the Southern Hemisphere monsoon (SHM) precipitation by 0.7%. Under the effect of tropical SAI, the reduced GM precipitation is mainly due to the thermodynamic term associated with the tropical cooling-induced decreased moisture content. The hemispheric antisymmetric impact of Arctic SAI arises from the dynamic term related to anomalous moisture convergence influenced by the anomalous meridional temperature gradient. ... There has been a number of proposals for managing solar radiation, or Solar Radiation Management (SRM). Two space-based approaches have been proposed; the deployment of space deflectors at the Lagrange 1 gravitational saddle point between the sun and the earth (Early 1989), or a ring of near-earth space mirrors (Wood 2012). ... Chapter Currently, climate change is a significant threat to our way of life, with global mean temperatures predicted to increase by 1.1-6.4°C by the end of the century (IPCC 2007). This increase is driven by multiple factors, with the main contributors being the increasing concentrations of Greenhouse Gases (GHG), mainly CO2, CH4 and N2O, in the atmosphere, which is altering the Earth's current energy balance and therefore the present climate. The current consensus within the scientific community is that the dominant factor in the changing climate of the Earth is the anthropogenic emission of GHG's, with the probability of this being true termed "very likely" (90% probability) by the IPCC (IPCC 2007). Whilst the main effort within the global community should be to control climate change by reducing our emissions of GHG's, it is prudent to investigate other methods of managing the climate system. The field of deliberately manipulating the Earth's climate is called geoengineering, or climate engineering. Article Full-text available Solar radiation management (SRM) geoengineering has been proposed as a potential option to counteract climate change. We perform a set of idealized geoengineering simulations to understand the global hydrological implications of varying the latitudinal distribution of solar insolation reduction in SRM methods. We find that for a fixed total mass of sulfate aerosols (12.6 Mt of SO4), relative to a uniform distribution which mitigates changes in global mean temperature, global mean radiative forcing is larger when aerosol concentration is maximum at the poles leading to a warmer global mean climate and consequently an intensified hydrological cycle. Opposite changes are simulated when aerosol concentration is maximized in the tropics. We obtain a range of 1 K in global mean temperature and 3% in precipitation changes by varying the distribution pattern: this range is about 50% of the climate change from a doubling of CO2. Hence, our study demonstrates that a range of global mean climate states, determined by the global mean radiative forcing, are possible for a fixed total amount of aerosols but with differing latitudinal distribution, highlighting the need for a careful evaluation of SRM proposals. Article [1] Sunshade geoengineering - the installation of reflective mirrors between the Earth and the Sun to reduce incoming solar radiation, has been proposed as a mitigative measure to counteract anthropogenic global warming. Although the popular conception is that geoengineering can re-establish a ‘natural’ pre-industrial climate, such a scheme would itself inevitably lead to climate change, due to the different temporal and spatial forcing of increased CO2 compared to reduced solar radiation. We investigate the magnitude and nature of this climate change for the first time within a fully coupled General Circulation Model. We find significant cooling of the tropics, warming of high latitudes and related sea ice reduction, a reduction in intensity of the hydrological cycle, reduced ENSO variability, and an increase in Atlantic overturning. However, the changes are small relative to those associated with an unmitigated rise in CO2 emissions. Other problems such as ocean acidification remain unsolved by sunshade geoengineering. Article The concept of deploying a large solar shield, or sunshade, near the Sun-Earth L1 Lagrange equilibrium point was first proposed in 1989. The purpose of such a solar shade would be to reduce the quantity of solar radiation impinging on planet Earth, thus lowering the average global surface temperature and countering, to some extent, global warming. This form of solar radiation management seems to be one of the safest and most efficient methods proposed to date but also seems to be extremely expensive and perhaps too difficult to implement in a timely manner. The near-term arrival of cheap, re-usable launch vehicles may be able to address both of these concerns. Depending on the assumptions made, deploying a solar shield near the Sun-Earth L1 point might actually be feasible in the near term and would be able to slow, stop, or even reverse Earth's global warming, even in the face of increasing levels of greenhouse gases in Earth's atmosphere. Solar radiation management doesn't address other environmental issues, such as the acidification of the world's oceans, but it does address the more urgent issue of impending global warming and the resulting climate change, thus buying time for the World's economies to transition to more sustainable, carbon-free energy sources. The infrastructure necessary to construct and deploy a large solar shield will probably be space-based and could be useful for many other purposes after deployment of the solar shield. Book Memoir commissioned by the National Air and Space Museum. Article Full-text available This editorial introduces a four-paper thematic section on ‘Insecure environments’, growing out of a conference session held in 2012. Through an excursion into Adorno and Horkheimer's Dialectic of Enlightenment (1979), themes are identified to do with the dialectic of security and insecurity, as played out in humanity's modern dealings with nature. The four papers are then formally outlined and situated in relation to these themes of (in)secure environments, the domination of nature and its many repercussions. Article This chapter provides an overview of space-based geoengineering as a tool to modulate solar insolation and offset the impacts of humandriven climate change. A range of schemes are considered including static and orbiting occulting disks and artificial dust clouds at the interior Sun-Earth Lagrange point, the gravitational balance point between the Sun and Earth. It is demonstrated that, in principle, a dust cloud can be gravitationally anchored at the interior Lagrange point to reduce solar insolation and that orbiting disks can provide a uniform reduction of solar insolation with latitude, potentially offsetting the regional impacts of a static disk. While clearly speculative, the investigation of space-based geoengineering schemes provides insights into the long-term prospects for large-scale, active control of solar insolation. Article Solar geoengineering has been proposed as a potential mechanism to counteract global warming. Here we use the University of Victoria Earth System Model (UVic) to simulate the effect of idealized sunshade geoengineering on the global carbon cycle. We conduct two simulations. The first is the A2 simulation, where the model is driven by prescribed emission scenario based on the SRES A2 CO2 emission pathway. The second is the solar geoengineering simulation in which the model is driven by the A2 CO2 emission scenario combined with sunshade solar geoengineering. In the model, solar geoengineering is represented by a spatially uniform reduction in solar insolation that is implemented at year 2020 to offset CO2-induced global mean surface temperature change. Our results show that solar geoengineering increases global carbon uptake relative to A2, in particular CO2 uptake by the terrestrial biosphere. The increase in land carbon uptake is mainly associated with increased net primary production (NPP) in the tropics in the geoengineering simulation, which prevents excess warming in tropics. By year 2100, solar geoengineering decreases A2-simulated atmospheric CO2 by 110 ppm (12%) and causes a 60% (251 Pg C) increase in land carbon accumulation compared to A2. Solar geoengineering also prevents the reduction in ocean oxygen concentration caused by increased ocean temperatures and decreased ocean ventilation, but reduces global ocean NPP. Our results suggest that to fully access the climate effect of solar geoengineering, the response of the global carbon cycle should be taken into account. Article Geoengineering has been proposed as a backup approach to rapidly cool the Earth and avoid damages associated with anthropogenic climate change. In this study, we use the NCAR Community Earth System Model to conduct a series of slab-ocean and prescribed sea surface temperature simulations to investigate the climate response to three proposed radiation management geoengineering schemes: stratospheric aerosol increase (SAI), marine cloud brightening (MCB), and cirrus cloud thinning (CCT). Our simulations show that different amounts of radiative forcing are needed for these three schemes to compensate global mean warming induced by a doubling of atmospheric CO2. With radiative forcing defined in terms of top-of-atmosphere energy imbalances in prescribed sea surface temperature simulations with land temperature adjustments, radiative forcing efficacy for SAI is about 15% smaller than that of CO2, and the efficacy for MCB and CCNCCT is about 10% larger than that of CO2. In our simulations, different forcing efficacies are associated with different feedback processes for these forcing agents. Also, these geoengineering schemes produce different land-ocean temperature change contrasts. The apparent hydrological sensitivity, that is, change in equilibrium global mean precipitation per degree of equilibrium temperature change, differs substantially between CO2, SAI, MCB, and CCNCCT forcings, which is mainly a result of different precipitation responses during fast adjustment. After removing the component of fast adjustment, the northward movement of the Intertropical Convergence Zone in response to these forcing agents is tightly related with changes in the interhemispheric energy exchange and hemispheric temperature gradient. Article So far, space-based geoengineering has rarely been studied from a practical point of view, considered unrealistic as a near-future alternative to fight climate change. This paper evaluates the feasibility of implementing a space sunshade in the vicinity of the first Lagrange point of the Sun-Earth system by the middle of the century. The analysis considers the necessary technological development, the possible trajectories for the shades, and an approximation of the size and cost of the system. It is strongly dependent on possible optical properties of future solar sails, so an optimal and a more conservative alternative have been studied. With the latter, the shade will be formed by 1.5×10⁹ sailcraft with a sail area of 2500 m² and a total mass of 8.3 × 10¹⁰ kg. In the optimal case, the total mass is 3.4 × 10¹⁰ kg. Each one of these sails will be launched to a 2000 km orbit, from where they will travel for about 600 days to the equilibrium point using solar radiation pressure. The total cost of the mission is estimated to be five to ten trillion dollars, based on a launch cost of US$50/kg. There are two main technological challenges for this to become a reality: the low TRL of the solar sails proposed and the necessary development in the launch vehicle industry given the dimensions of the mission.
Article
In this paper a method of geoengineering is proposed involving clouds of dust placed in the vicinity of the L1 point as an alternative to the use of thin film reflectors. The aim of this scheme is to reduce the manufacturing requirement for space-based geoengineering. It has been concluded that the mass requirement for a cloud placed at the classical L1 point, to create an average solar insolation reduction of 1.7%, is 7.60 × 1010 kg yr−1 whilst a cloud placed at a displaced equilibrium point created by the inclusion of the effect of solar radiation pressure is 1.87 × 1010 kg yr−1. These mass ejection rates are considerably less than the mass required in other unprocessed dust cloud methods proposed and are comparable to thin film reflector geoengineering requirements. Importantly, unprocessed dust sourced in-situ is seen as an attractive scheme compared to highly engineered thin film reflectors. It is envisaged that the required mass of dust can be extracted from captured near Earth asteroids, whilst stabilised in the required position using the impulse provided by solar collectors or mass drivers used to eject material from the asteroid surface.
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