Fe(II)Cl2 amendment suppresses pond methane emissions by stimulating iron-dependent anaerobic oxidation of methane

Aquatic ecosystems are large contributors to global methane (CH4) emissions. Eutrophication significantly enhances CH4-production as it stimulates methanogenesis. Mitigation measures aimed at reducing eutrophication, such as the addition of metal salts to immobilize phosphate (PO43-), are now common practice. However, the effects of such remedies on methanogenic and methanotrophic communities-and therefore on CH4-cycling-remain largely unexplored. Here, we demonstrate that Fe(II)Cl2 addition, used as PO43- binder, differentially affected microbial CH4 cycling-processes in field experiments and batch incubations. In the field experiments, carried out in enclosures in a eutrophic pond, Fe(II)Cl2 application lowered in-situ CH4 emissions by lowering net CH4-production, while sediment aerobic CH4-oxidation rates-as found in batch incubations of sediment from the enclosures-did not differ from control. In Fe(II)Cl2-treated sediments, a decrease in net CH4-production rates could be attributed to the stimulation of iron-dependent anaerobic CH4-oxidation (Fe-AOM). In batch incubations, anaerobic CH4-oxidation and Fe(II)-production started immediately after CH4 addition, indicating Fe-AOM, likely enabled by favorable indigenous iron cycling conditions and the present methanotroph community in the pond sediment. 16S rRNA sequencing data confirmed the presence of anaerobic CH4-oxidizing archaea and both iron-reducing and iron-oxidizing bacteria in the tested sediments. Thus, besides combatting eutrophication, Fe(II)Cl2 application can mitigate CH4 emissions by reducing microbial net CH4-production and stimulating Fe-AOM.

'It's just a Band-Aid!': Public engagement with geoengineering and the politics of the climate crisis

Geoengineering consists of a set of techniques whose aim is to avoid the disastrous consequences of global warming, such as solar radiation management and carbon dioxide removal. Due to its controversial nature, over the past decade various exercises of public participation with geoengineering have been put in place, particularly in the Global North. This article draws on empirical data stemming from six online focus groups on public engagement with geoengineering conducted in Portugal. In contrast to previous research, we included situated publics to emphasize the political implications of geoengineering, bringing to the debate those with a potential stake in the matter - environmentalists, activists, university students, science communicators and promoters of holistic practices. We suggest that the elusive and uncertain character of geoengineering moves the discussion away from its technological specificity, bringing to the fore some of the socio-political, economic and ethical tensions underpinning the climate crisis.

Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover

Discussions of countering global warming with solar geoengineering assume that warming owing to rising greenhouse-gas concentrations can be compensated by artificially reducing the amount of sunlight Earth absorbs. However, solar geoengineering may not be fail-safe to prevent global warming because CO₂ can directly affect cloud cover: It reduces cloud cover by modulating the longwave radiative cooling within the atmosphere. This effect is not mitigated by solar geoengineering. Here, we use idealized high-resolution simulations of clouds to show that, even under a sustained solar geoengineering scenario with initially only modest warming, subtropical stratocumulus clouds gradually thin and may eventually break up into scattered cumulus clouds, at concentrations exceeding 1,700 parts per million (ppm). Because stratocumulus clouds cover large swaths of subtropical oceans and cool Earth by reflecting incident sunlight, their loss would trigger strong (about 5 K) global warming. Thus, the results highlight that, at least in this extreme and idealized scenario, solar geoengineering may not suffice to counter greenhouse-gas-driven global warming.

Solar geoengineering may lead to excessive cooling and high strategic uncertainty

Climate engineering-the deliberate large-scale manipulation of the Earth's climate system-is a set of technologies for reducing climate-change impacts and risks. It is controversial and raises novel governance challenges [T. C. Schelling, Climatic Change, 33, 303-307 (1996); J. Virgoe, Climatic Change, 95, 103-119 (2008)]. We focus on the strategic implications of solar geoengineering. When countries engineer the climate, conflict can arise because different countries might prefer different temperatures. This would result in too much geoengineering: the country with the highest preference for geoengineering cools the planet beyond what is socially optimal at the expense of the others-a theoretical possibility termed "free-driving" [M. L. Weitzman, Scand. J. Econ., 117, 1049-1068 (2015)]. This study is an empirical test of this hypothesis. We carry out an economic laboratory experiment based on a public "good or bad" game. We find compelling evidence of free-driving: global geoengineering exceeds the socially efficient level and leads to welfare losses. We also evaluate the possibility of counteracting the geoengineering efforts of others. Results show that countergeoengineering generates high payoff inequality as well as heavy welfare losses, resulting from both strategic and behavioral factors. Finally, we compare strategic behavior in bilateral and multilateral settings. We find that welfare deteriorates even more under multilateralism when countergeoengineering is a possibility. These results have general implications for governing global good or bad commons.

Effects of Sea Salt Aerosol Emissions for Marine Cloud Brightening on Atmospheric Chemistry: Implications for Radiative Forcing

Marine cloud brightening (MCB) is proposed to offset global warming by emitting sea salt aerosols to the tropical marine boundary layer, which increases aerosol and cloud albedo. Sea salt aerosol is the main source of tropospheric reactive chlorine (Cl y ) and bromine (Br y ). The effects of additional sea salt on atmospheric chemistry have not been explored. We simulate sea salt aerosol injections for MCB under two scenarios (212-569 Tg/a) in the GEOS-Chem global chemical transport model, only considering their impacts as a halogen source. Globally, tropospheric Cl y and Br y increase (20-40%), leading to decreased ozone (-3 to -6%). Consequently, OH decreases (-3 to -5%), which increases the methane lifetime (3-6%). Our results suggest that the chemistry of the additional sea salt leads to minor total radiative forcing compared to that of the sea salt aerosol itself (~2%) but may have potential implications for surface ozone pollution in tropical coastal regions.

Pleistocene Arctic megafaunal ecological engineering as a natural climate solution?

Natural climate solutions (NCS) in the Arctic hold the potential to be implemented at a scale able to substantially affect the global climate. The strong feedbacks between carbon-rich permafrost, climate and herbivory suggest an NCS consisting of reverting the current wet/moist moss and shrub-dominated tundra and the sparse forest-tundra ecotone to grassland through a guild of large herbivores. Grassland-dominated systems might delay permafrost thaw and reduce carbon emissions-especially in Yedoma regions, while increasing carbon capture through increased productivity and grass and forb deep root systems. Here we review the environmental context of megafaunal ecological engineering in the Arctic; explore the mechanisms through which it can help mitigate climate change; and estimate its potential-based on bison and horse, with the aim of evaluating the feasibility of generating an ecosystem shift that is economically viable in terms of carbon benefits and of sufficient scale to play a significant role in global climate change mitigation. Assuming a megafaunal-driven ecosystem shift we find support for a megafauna-based arctic NCS yielding substantial income in carbon markets. However, scaling up such projects to have a significant effect on the global climate is challenging given the large number of animals required over a short period of time. A first-cut business plan is presented based on practical information-costs and infrastructure-from Pleistocene Park (northeastern Yakutia, Russia). A 10 yr experimental phase incorporating three separate introductions of herds of approximately 1000 individuals each is costed at US$114 million, with potential returns of approximately 0.3-0.4% yr^-1 towards the end of the period, and greater than 1% yr^-1 after it. Institutional friction and the potential role of new technologies in the reintroductions are discussed. This article is part of the theme issue 'Climate change and ecosystems: threats, opportunities and solutions'.

Solar geoengineering to reduce climate change: a review of governance proposals

Although solar geoengineering (alternatively 'solar radiation management' or 'solar radiation modification') appears to offer a potentially effective, inexpensive and technologically feasible additional response to climate change, it would pose serious physical risks and social challenges. Governance of its research, development and deployment is thus salient. This article reviews proposals for governing solar geoengineering. Its research may warrant dedicated governance to facilitate effectiveness and to reduce direct and socially mediated risks. Because states are not substantially engaging with solar geoengineering, non-state actors can play important governance roles. Although the concern that solar geoengineering would harmfully lessen abatement of greenhouse gas emissions is widespread, what can be done to reduce such displacement remains unclear. A moratorium on outdoor activities that would surpass certain scales is often endorsed, but an effective one would require resolving some critical, difficult details. In the long term, how to legitimately make decisions regarding whether, when and how solar geoengineering would be used is central, and suggestions how to do so diverge. Most proposals to govern commercial actors, who could provide goods and services for solar geoengineering, focus on intellectual property policy. Compensation for possible harm from outdoor activities could be through liability or a compensation fund. The review closes with suggested lines of future inquiry.

Mission-driven research for stratospheric aerosol geoengineering

The last decade has seen broad exploratory research into stratospheric aerosol (SA) geoengineering, motivated by concern that reducing greenhouse gas emissions may be insufficient to avoid significant impacts from climate change. Based on this research, it is plausible that a limited deployment of SA geoengineering, provided it is used in addition to cutting emissions, could reduce many climate risks for most people. However, "plausible" is an insufficient basis on which to support future decisions. Developing the necessary knowledge requires a transition toward mission-driven research that has the explicit goal of supporting informed decisions. We highlight two important observations that follow from considering such a comprehensive, prioritized natural-science research effort. First, while field experiments may eventually be needed to reduce some of the uncertainties, we expect that the next phase of research will continue to be primarily model-based, with one outcome being to assess and prioritize which uncertainties need to be reduced (and, as a corollary, which field experiments can reduce those uncertainties). Second, we anticipate a clear separation in scale and character between small-scale experimental research to resolve specific process uncertainties and global-scale activities. We argue that the latter, even if the radiative forcing is negligible, should more appropriately be considered after a decision regarding whether and how to deploy SA geoengineering, rather than within the scope of "research" activities.

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'.

Negative emissions technologies and carbon capture and storage to achieve the Paris Agreement commitments

How will the global atmosphere and climate be protected? Achieving net-zero CO₂ emissions will require carbon capture and storage (CCS) to reduce current GHG emission rates, and negative emissions technology (NET) to recapture previously emitted greenhouse gases. Delivering NET requires radical cost and regulatory innovation to impact on climate mitigation. Present NET exemplars are few, are at small-scale and not deployable within a decade, with the exception of rock weathering, or direct injection of CO₂ into selected ocean water masses. To keep warming less than 2°C, bioenergy with CCS (BECCS) has been modelled but does not yet exist at industrial scale. CCS already exists in many forms and at low cost. However, CCS has no political drivers to enforce its deployment. We make a new analysis of all global CCS projects and model the build rate out to 2050, deducing this is 100 times too slow. Our projection to 2050 captures just 700 Mt CO₂ yr^-1, not the minimum 6000 Mt CO₂ yr^-1 required to meet the 2°C target. Hence new policies are needed to incentivize commercial CCS. A first urgent action for all countries is to commercially assess their CO₂ storage. A second simple action is to assign a Certificate of CO₂ Storage onto producers of fossil carbon, mandating a progressively increasing proportion of CO₂ to be stored. No CCS means no 2°C.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'.

Negative emissions technologies and carbon capture and storage to achieve the Paris Agreement commitments

How will the global atmosphere and climate be protected? Achieving net-zero CO₂ emissions will require carbon capture and storage (CCS) to reduce current GHG emission rates, and negative emissions technology (NET) to recapture previously emitted greenhouse gases. Delivering NET requires radical cost and regulatory innovation to impact on climate mitigation. Present NET exemplars are few, are at small-scale and not deployable within a decade, with the exception of rock weathering, or direct injection of CO₂ into selected ocean water masses. To keep warming less than 2°C, bioenergy with CCS (BECCS) has been modelled but does not yet exist at industrial scale. CCS already exists in many forms and at low cost. However, CCS has no political drivers to enforce its deployment. We make a new analysis of all global CCS projects and model the build rate out to 2050, deducing this is 100 times too slow. Our projection to 2050 captures just 700 Mt CO₂ yr^-1, not the minimum 6000 Mt CO₂ yr^-1 required to meet the 2°C target. Hence new policies are needed to incentivize commercial CCS. A first urgent action for all countries is to commercially assess their CO₂ storage. A second simple action is to assign a Certificate of CO₂ Storage onto producers of fossil carbon, mandating a progressively increasing proportion of CO₂ to be stored. No CCS means no 2°C.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'.

An Analysis of the Optimal Mix of Global Energy Resources and the Potential Need for Geoengineering Using the CEAGOM Model

Humanity faces tremendous challenges as a result of anthropogenic climate change caused by greenhouse gas emissions. The mix of resources deployed in order to meet the energy needs of a growing global population is key to addressing the climate change issue. The goal of this research is to examine the optimal mix of energy resources that should be deployed to meet a forecast global energy demand while still meeting desired climate targets. The research includes the unique feature of examining the role that geoengineering can play in this optimization. The results show that some form of geoengineering is likely to be needed by the middle of the 21st century as part of the optimal energy strategy in order to meet a specified climate goal of 580 ppm CO2-eq greenhouse gas concentration (or ≈2 °C average global temperature rise). The optimal energy mix would need to rely on energy efficiency, nuclear, geothermal, hydro, and wind energy for over 50% of global energy needs. In addition, the overall cost of the optimal energy mix is sensitive to the assumed amount of achievable energy efficiency, carbon taxes, deployment of electric vehicles, and the assumed discount rate.

The international politics of geoengineering: The feasibility of Plan B for tackling climate change

Geoengineering technologies aim to make large-scale and deliberate interventions in the climate system possible. A typical framing is that researchers are exploring a 'Plan B' in case mitigation fails to avert dangerous climate change. Some options are thought to have the potential to alter the politics of climate change dramatically, yet in evaluating whether they might ultimately reduce climate risks, their political and security implications have so far not been given adequate prominence. This article puts forward what it calls the 'security hazard' and argues that this could be a crucial factor in determining whether a technology is able, ultimately, to reduce climate risks. Ideas about global governance of geoengineering rely on heroic assumptions about state rationality and a generally pacific international system. Moreover, if in a climate engineered world weather events become something certain states can be made directly responsible for, this may also negatively affect prospects for 'Plan A', i.e. an effective global agreement on mitigation.

Crafting a public for geoengineering

In a short period of time, climate 'geoengineering' has been added to the list of technoscientific issues subject to deliberative public engagement. Here, we analyse this rapid trajectory of publicization and explore the particular manner in which the possibility of intentionally altering the Earth's climate system to curb global warming has been incorporated into the field of 'public engagement with science'. We describe the initial framing of geoengineering as a singular object of debate and subsequent attempts to 'unframe' the issue by placing it within broader discursive fields. The tension implicit in these processes of structured debate - how to turn geoengineering into a workable object of deliberation without implying a commitment to its reality as a policy option - raises significant questions about the role of 'public engagement with science' scholars and methods in facilitating public debate on speculative technological futures.

Stratospheric solar geoengineering without ozone loss

Injecting sulfate aerosol into the stratosphere, the most frequently analyzed proposal for solar geoengineering, may reduce some climate risks, but it would also entail new risks, including ozone loss and heating of the lower tropical stratosphere, which, in turn, would increase water vapor concentration causing additional ozone loss and surface warming. We propose a method for stratospheric aerosol climate modification that uses a solid aerosol composed of alkaline metal salts that will convert hydrogen halides and nitric and sulfuric acids into stable salts to enable stratospheric geoengineering while reducing or reversing ozone depletion. Rather than minimizing reactive effects by reducing surface area using high refractive index materials, this method tailors the chemical reactivity. Specifically, we calculate that injection of calcite (CaCO₃) aerosol particles might reduce net radiative forcing while simultaneously increasing column ozone toward its preanthropogenic baseline. A radiative forcing of -1 W⋅m^-2, for example, might be achieved with a simultaneous 3.8% increase in column ozone using 2.1 Tg⋅y^-1 of 275-nm radius calcite aerosol. Moreover, the radiative heating of the lower stratosphere would be roughly 10-fold less than if that same radiative forcing had been produced using sulfate aerosol. Although solar geoengineering cannot substitute for emissions cuts, it may supplement them by reducing some of the risks of climate change. Further research on this and similar methods could lead to reductions in risks and improved efficacy of solar geoengineering methods.

Potential negative consequences of geoengineering on crop production: A study of Indian groundnut

Geoengineering has been proposed to stabilize global temperature, but its impacts on crop production and stability are not fully understood. A few case studies suggest that certain crops are likely to benefit from solar dimming geoengineering, yet we show that geoengineering is projected to have detrimental effects for groundnut. Using an ensemble of crop-climate model simulations, we illustrate that groundnut yields in India undergo a statistically significant decrease of up to 20% as a result of solar dimming geoengineering relative to RCP4.5. It is somewhat reassuring, however, to find that after a sustained period of 50 years of geoengineering crop yields return to the nongeoengineered values within a few years once the intervention is ceased.

Developing a test-bed for robust research governance of geoengineering: the contribution of ocean iron biogeochemistry

Geoengineering to mitigate climate change has long been proposed, but remains nebulous. Exploration of the feasibility of geoengineering first requires the development of research governance to move beyond the conceptual towards scientifically designed pilot studies. Fortuitously, 12 mesoscale (approx. 1000 km2) iron enrichments, funded to investigate how ocean iron biogeochemistry altered Earth's carbon cycle in the geological past, provide proxies to better understand the benefits and drawbacks of geoengineering. The utility of these iron enrichments in the geoengineering debate is enhanced by the GEOTRACES global survey. Here, we outline how GEOTRACES surveys and process studies can provide invaluable insights into geoengineering. Surveys inform key unknowns including the regional influence and magnitude of modes of iron supply, and stimulate iron biogeochemical modelling. These advances will enable quantification of interannual variability of iron supply to assess whether any future purposeful multi-year iron-fertilization meets the principle of 'additionality' (sensu Kyoto protocol). Process studies address issues including upscaling of geoengineering, and how differing iron-enrichment strategies could stimulate wide-ranging biogeochemical outcomes. In summary, the availability of databases on both mesoscale iron-enrichment studies and the GEOTRACES survey, along with modelling, policy initiatives and legislation have positioned the iron-enrichment approach as a robust multifaceted test-bed to assess proposed research into climate intervention.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Human and Environmental Dangers Posed by Ongoing Global Tropospheric Aerosolized Particulates for Weather Modification

BACKGROUND

U.S. military perception of nuclear warfare led to countless unethical nuclear experiments performed on unsuspecting individuals without their informed consent. As evidenced here, subsequent perception of weather warfare has led to exposing millions of unsuspecting individuals to toxic coal fly ash with no public disclosure, no informed consent, and no health warnings.

METHODS

Three methods were used: (1) comparison of eight elements analyzed in rainwater samples, thought to have leached from aerosolized coal fly ash, with corresponding coal fly ash laboratory leachate; (2) comparison of 14 elements analyzed in air filter dust with corresponding elements in coal fly ash; and (3) comparison of 23 elements analyzed in fibrous mesh found after snow melted with corresponding elements in coal fly ash.

RESULTS

The rainwater element ratios show that the aerial particulate matter has essentially the same water-leach characteristics as coal fly ash. The air filter dust element ratios occur in the same range of compositions as coal fly ash, as do element ratios in fibrous mesh found on grass after snow melted. The fibrous mesh provides an inferred direct connection with the aerosolizing jet aircraft via coal fly ash association with the jet combustion environment.

CONCLUSION

Strong evidence for the correctness of the hypothesis: coal fly ash is likely the aerosolized particulate emplaced in the troposphere for geoengineering, weather modification, and/or climate alteration purposes. The documented public health associations for ≤2.5 μm particulate pollution are also applicable to aerosolized coal fly ash. The ability of coal fly ash to release aluminum in a chemically mobile form upon exposure to water or body moisture has potentially grave human and environmental consequences over a broad spectrum, including implications for neurological diseases and biota debilitation. The ability of coal fly ash to release heavy metals and radioactive elements upon exposure to body moisture has potentially grave human health implications including cancer, cardiovascular disease, diabetes, respiratory diseases, reduced male fertility, and stroke. The fibrous mesh data admit the possibility of environmentally disastrous formation of methylmercury and ozone-depleting chlorinated-fluorinated hydrocarbons in jet exhaust. Geophysical implications include atmospheric warming and rainfall retardation.

Using decision pathway surveys to inform climate engineering policy choices

Over the coming decades citizens living in North America and Europe will be asked about a variety of new technological and behavioral initiatives intended to mitigate the worst impacts of climate change. A common approach to public input has been surveys whereby respondents' attitudes about climate change are explained by individuals' demographic background, values, and beliefs. In parallel, recent deliberative research seeks to more fully address the complex value tradeoffs linked to novel technologies and difficult ethical questions that characterize leading climate mitigation alternatives. New methods such as decision pathway surveys may offer important insights for policy makers by capturing much of the depth and reasoning of small-group deliberations while meeting standard survey goals including large-sample stakeholder engagement. Pathway surveys also can help participants to deepen their factual knowledge base and arrive at a more complete understanding of their own values as they apply to proposed policy alternatives. The pathway results indicate more fully the conditional and context-specific nature of support for several "upstream" climate interventions, including solar radiation management techniques and carbon dioxide removal technologies.

Assessing the direct occupational and public health impacts of solar radiation management with stratospheric aerosols

Geoengineering is the deliberate large-scale manipulation of environmental processes that affects the Earth's climate, in an attempt to counteract the effects of climate change. Injecting sulfate aerosol precursors and designed nanoparticles into the stratosphere to (i.e., solar radiation management [SRM]), has been suggested as one approach to geoengineering. Although much is being done to unravel the scientific and technical challenges around geoengineering, there have been few efforts to characterize the potential human health impacts of geoengineering, particularly with regards to SRM approaches involving stratospheric aerosols. This paper explores this information gap. Using available evidence, we describe the potential direct occupational and public health impacts of exposures to aerosols likely to be used for SRM, including environmental sulfates, black carbon, metallic aluminum, and aluminum oxide aerosols. We speculate on possible health impacts of exposure to one promising SRM material, barium titanate, using knowledge of similar nanomaterials. We also explore current regulatory efforts to minimize exposure to these toxicants. Our analysis suggests that adverse public health impacts may reasonably be expected from SRM via deployment of stratospheric aerosols. Little is known about the toxicity of some likely candidate aerosols, and there is no consensus regarding acceptable levels for public exposure to these materials. There is also little infrastructure in place to evaluate potential public health impacts in the event that stratospheric aerosols are deployed for solar radiation management. We offer several recommendations intended to help characterize the potential occupation and public health impacts of SRM, and suggest that a comprehensive risk assessment effort is needed before this approach to geoengineering receives further consideration.

Evidence of Coal-Fly-Ash Toxic Chemical Geoengineering in the Troposphere: Consequences for Public Health

The widespread, intentional and increasingly frequent chemical emplacement in the troposphere has gone unidentified and unremarked in the scientific literature for years. The author presents evidence that toxic coal combustion fly ash is the most likely aerosolized particulate sprayed by tanker-jets for geoengineering, weather-modification and climate-modification purposes and describes some of the multifold consequences on public health. Two methods are employed: (1) Comparison of 8 elements analyzed in rainwater, leached from aerosolized particulates, with corresponding elements leached into water from coal fly ash in published laboratory experiments, and (2) Comparison of 14 elements analyzed in dust collected outdoors on a high-efficiency particulate air (HEPA) filter with corresponding elements analyzed in un-leached coal fly ash material. The results show: (1) the assemblage of elements in rainwater and in the corresponding experimental leachate are essentially identical. At a 99% confidence interval, they have identical means (T-test) and identical variances (F-test); and (2) the assemblage of elements in the HEPA dust and in the corresponding average un-leached coal fly ash are likewise essentially identical. The consequences on public health are profound, including exposure to a variety of toxic heavy metals, radioactive elements, and neurologically-implicated chemically mobile aluminum released by body moisture in situ after inhalation or through transdermal induction.

Asilomar moments: formative framings in recombinant DNA and solar climate engineering research

We examine the claim that in governance for solar climate engineering research, and especially field tests, there is no need for external governance beyond existing mechanisms such as peer review and environmental impact assessments that aim to assess technically defined risks to the physical environment. By drawing on the historical debate on recombinant DNA research, we show that defining risks is not a technical question but a complex process of narrative formation. Governance emerges from within, and as a response to, narratives of what is at stake in a debate. In applying this finding to the case of climate engineering, we find that the emerging narrative differs starkly from the narrative that gave meaning to rDNA technology during its formative period, with important implications for governance. While the narrative of rDNA technology was closed down to narrowly focus on technical risks, that of climate engineering continues to open up and includes social, political and ethical issues. This suggests that, in order to be legitimate, governance must take into account this broad perception of what constitutes the relevant issues and risks of climate engineering, requiring governance that goes beyond existing mechanisms that focus on technical risks. Even small-scale field tests with negligible impacts on the physical environment warrant additional governance as they raise broader concerns that go beyond the immediate impacts of individual experiments.

Ethical aspects of the mitigation obstruction argument against climate engineering research

Many commentators fear that climate engineering research might lead policy-makers to reduce mitigation efforts. Most of the literature on this so-called 'moral hazard' problem focuses on the prediction that climate engineering research would reduce mitigation efforts. This paper focuses on a related ethical question: Why would it be a bad thing if climate engineering research obstructed mitigation? If climate engineering promises to be effective enough, it might justify some reduction in mitigation. Climate policy portfolios involving sufficiently large or poorly planned reductions in mitigation, however, could lead to an outcome that would be worse than the portfolio that would be chosen in the absence of further climate engineering research. This paper applies three ethical perspectives to describe the kinds of portfolios that would be worse than that 'baseline portfolio'. The literature on climate engineering identifies various mechanisms that might cause policy-makers to choose these inferior portfolios, but it is difficult to know in advance whether the existence of these mechanisms means that climate engineering research really would lead to a worse outcome. In the light of that uncertainty, a precautionary approach suggests that researchers should take measures to reduce the risk of mitigation obstruction. Several such measures are suggested.

Geoengineering, climate change scepticism and the 'moral hazard' argument: an experimental study of UK public perceptions

Many commentators have expressed concerns that researching and/or developing geoengineering technologies may undermine support for existing climate policies-the so-called moral hazard argument. This argument plays a central role in policy debates about geoengineering. However, there has not yet been a systematic investigation of how members of the public view the moral hazard argument, or whether it impacts on people's beliefs about geoengineering and climate change. In this paper, we describe an online experiment with a representative sample of the UK public, in which participants read one of two arguments (either endorsing or rejecting the idea that geoengineering poses a moral hazard). The argument endorsing the idea of geoengineering as a moral hazard was perceived as more convincing overall. However, people with more sceptical views and those who endorsed 'self-enhancing' values were more likely to agree that the prospect of geoengineering would reduce their motivation to make changes in their own behaviour in response to climate change. The findings suggest that geoengineering is likely to pose a moral hazard for some people more than others, and the implications for engaging the public are discussed.

Mapping the landscape of climate engineering

In the absence of a governance framework for climate engineering technologies such as solar radiation management (SRM), the practices of scientific research and intellectual property acquisition can de facto shape the development of the field. It is therefore important to make visible emerging patterns of research and patenting, which we suggest can effectively be done using bibliometric methods. We explore the challenges in defining the boundary of climate engineering, and set out the research strategy taken in this study. A dataset of 825 scientific publications on climate engineering between 1971 and 2013 was identified, including 193 on SRM; these are analysed in terms of trends, institutions, authors and funders. For our patent dataset, we identified 143 first filings directly or indirectly related to climate engineering technologies-of which 28 were related to SRM technologies-linked to 910 family members. We analyse the main patterns discerned in patent trends, applicants and inventors. We compare our own findings with those of an earlier bibliometric study of climate engineering, and show how our method is consistent with the need for transparency and repeatability, and the need to adjust the method as the field develops. We conclude that bibliometric monitoring techniques can play an important role in the anticipatory governance of climate engineering.

Modelling artificial sea salt emission in large eddy simulations

We study the dispersion of sea salt particles from artificially injected sea spray at a cloud-resolving scale. Understanding of how different aerosol processes affect particle dispersion is crucial when designing emission sources for marine cloud brightening. Compared with previous studies, we include for the first time an explicit treatment of aerosol water, which takes into account condensation, evaporation and their effect on ambient temperature. This enables us to capture the negative buoyancy caused by water evaporation from aerosols. Additionally, we use a higher model resolution to capture aerosol loss through coagulation near the source point. We find that, with a seawater flux of 15 kg s(-1), the cooling due to evaporation can be as much as 1.4 K, causing a delay in particle dispersion of 10-20 min. This delay enhances particle scavenging by a factor of 1.14 compared with simulations without aerosol water. We further show that both cooling and particle dispersion depend on the model resolution, with a maximum particle scavenging efficiency of 20% within 5 h after emission at maximum resolution of 50 m. Based on these results, we suggest further regional high-resolution studies which model several injection periods over several weeks.

Solar geoengineering to limit the rate of temperature change

Solar geoengineering has been suggested as a tool that might reduce damage from anthropogenic climate change. Analysis often assumes that geoengineering would be used to maintain a constant global mean temperature. Under this scenario, geoengineering would be required either indefinitely (on societal time scales) or until atmospheric CO2 concentrations were sufficiently reduced. Impacts of climate change, however, are related to the rate of change as well as its magnitude. We thus describe an alternative scenario in which solar geoengineering is used only to constrain the rate of change of global mean temperature; this leads to a finite deployment period for any emissions pathway that stabilizes global mean temperature. The length of deployment and amount of geoengineering required depends on the emissions pathway and allowable rate of change, e.g. in our simulations, reducing the maximum approximately 0.3°C per decade rate of change in an RCP 4.5 pathway to 0.1°C per decade would require geoengineering for 160 years; under RCP 6.0, the required time nearly doubles. We demonstrate that feedback control can limit rates of change in a climate model. Finally, we note that a decision to terminate use of solar geoengineering does not automatically imply rapid temperature increases: feedback could be used to limit rates of change in a gradual phase-out.

Factors determining the most efficient spray distribution for marine cloud brightening

We investigate the sensitivity of marine cloud brightening to the properties of the added salt particle distribution using a cloud parcel model, with an aim to address the question of, 'what is the most efficient particle size distribution that will produce a desired cooling effect?' We examine the effect that altering the aerosol particle size distribution has on the activation and growth of drops, i.e. the Twomey effect alone, and do not consider macrophysical cloud responses that may enhance or mitigate the Twomey effect. For all four spray generation methods considered, Rayleigh jet; Taylor cone jet; supercritical fluid; and effervescent spray, salt particles within the median dry diameter range Dm=30-100 nm are the most effective range of sizes. The Rayleigh jet method is also the most energy efficient overall. We also find that care needs to be taken when using droplet activation parametrizations: for the concentrations considered, Aitken particles do not result in a decrease in the total albedo, as was found in a recent study, and such findings are likely to be a result of the parametrizations' inability to simulate the effect of swollen aerosol particles. Our findings suggest that interstitial aerosol particles play a role in controlling the albedo rather than just the activated cloud drops, which is an effect that the parametrization methods do not consider.

Stratospheric controlled perturbation experiment: a small-scale experiment to improve understanding of the risks of solar geoengineering

Although solar radiation management (SRM) through stratospheric aerosol methods has the potential to mitigate impacts of climate change, our current knowledge of stratospheric processes suggests that these methods may entail significant risks. In addition to the risks associated with current knowledge, the possibility of 'unknown unknowns' exists that could significantly alter the risk assessment relative to our current understanding. While laboratory experimentation can improve the current state of knowledge and atmospheric models can assess large-scale climate response, they cannot capture possible unknown chemistry or represent the full range of interactive atmospheric chemical physics. Small-scale, in situ experimentation under well-regulated circumstances can begin to remove some of these uncertainties. This experiment-provisionally titled the stratospheric controlled perturbation experiment-is under development and will only proceed with transparent and predominantly governmental funding and independent risk assessment. We describe the scientific and technical foundation for performing, under external oversight, small-scale experiments to quantify the risks posed by SRM to activation of halogen species and subsequent erosion of stratospheric ozone. The paper's scope includes selection of the measurement platform, relevant aspects of stratospheric meteorology, operational considerations and instrument design and engineering.

Geoengineering, news media and metaphors: Framing the controversial

We analyze how metaphors are used in presenting and debating novel technologies that could influence the climate and thereby also future climate change policies. We show that metaphors strengthen a policy-related storyline, while metaphors are rarer in purely descriptive accounts. The choice of metaphor frames the technologies. War metaphors are used equally in arguments that are for, against and neutral with respect to the further development of geoengineering, but differences arise in the use of metaphors related to controllability, health and mechanisms. Controllability metaphors are often used in justifying further research and development of good governance practices, whereas health metaphors tend to be used against the very idea of geoengineering by portraying technological interventions in the climate as an emblematic case of an unacceptable development. These findings suggest that metaphors are early indications of restrictions in the interpretative flexibility that influences future governance of geoengineering and geoengineering research.

Ocean acidification in a geoengineering context

Fundamental changes to marine chemistry are occurring because of increasing carbon dioxide (CO(2)) in the atmosphere. Ocean acidity (H(+) concentration) and bicarbonate ion concentrations are increasing, whereas carbonate ion concentrations are decreasing. There has already been an average pH decrease of 0.1 in the upper ocean, and continued unconstrained carbon emissions would further reduce average upper ocean pH by approximately 0.3 by 2100. Laboratory experiments, observations and projections indicate that such ocean acidification may have ecological and biogeochemical impacts that last for many thousands of years. The future magnitude of such effects will be very closely linked to atmospheric CO(2); they will, therefore, depend on the success of emission reduction, and could also be constrained by geoengineering based on most carbon dioxide removal (CDR) techniques. However, some ocean-based CDR approaches would (if deployed on a climatically significant scale) re-locate acidification from the upper ocean to the seafloor or elsewhere in the ocean interior. If solar radiation management were to be the main policy response to counteract global warming, ocean acidification would continue to be driven by increases in atmospheric CO(2), although with additional temperature-related effects on CO(2) and CaCO(3) solubility and terrestrial carbon sequestration.

Marine cloud brightening

The idea behind the marine cloud-brightening (MCB) geoengineering technique is that seeding marine stratocumulus clouds with copious quantities of roughly monodisperse sub-micrometre sea water particles might significantly enhance the cloud droplet number concentration, and thereby the cloud albedo and possibly longevity. This would produce a cooling, which general circulation model (GCM) computations suggest could-subject to satisfactory resolution of technical and scientific problems identified herein-have the capacity to balance global warming up to the carbon dioxide-doubling point. We describe herein an account of our recent research on a number of critical issues associated with MCB. This involves (i) GCM studies, which are our primary tools for evaluating globally the effectiveness of MCB, and assessing its climate impacts on rainfall amounts and distribution, and also polar sea-ice cover and thickness; (ii) high-resolution modelling of the effects of seeding on marine stratocumulus, which are required to understand the complex array of interacting processes involved in cloud brightening; (iii) microphysical modelling sensitivity studies, examining the influence of seeding amount, seed-particle salt-mass, air-mass characteristics, updraught speed and other parameters on cloud-albedo change; (iv) sea water spray-production techniques; (v) computational fluid dynamics studies of possible large-scale periodicities in Flettner rotors; and (vi) the planning of a three-stage limited-area field research experiment, with the primary objectives of technology testing and determining to what extent, if any, cloud albedo might be enhanced by seeding marine stratocumulus clouds on a spatial scale of around 100×100 km. We stress that there would be no justification for deployment of MCB unless it was clearly established that no significant adverse consequences would result. There would also need to be an international agreement firmly in favour of such action.

Ecosystem impacts of geoengineering: a review for developing a science plan

Geoengineering methods are intended to reduce climate change, which is already having demonstrable effects on ecosystem structure and functioning in some regions. Two types of geoengineering activities that have been proposed are: carbon dioxide (CO(2)) removal (CDR), which removes CO(2) from the atmosphere, and solar radiation management (SRM, or sunlight reflection methods), which reflects a small percentage of sunlight back into space to offset warming from greenhouse gases (GHGs). Current research suggests that SRM or CDR might diminish the impacts of climate change on ecosystems by reducing changes in temperature and precipitation. However, sudden cessation of SRM would exacerbate the climate effects on ecosystems, and some CDR might interfere with oceanic and terrestrial ecosystem processes. The many risks and uncertainties associated with these new kinds of purposeful perturbations to the Earth system are not well understood and require cautious and comprehensive research.

How does the Earth system generate and maintain thermodynamic disequilibrium and what does it imply for the future of the planet?

The Earth's chemical composition far from chemical equilibrium is unique in our Solar System, and this uniqueness has been attributed to the presence of widespread life on the planet. Here, I show how this notion can be quantified using non-equilibrium thermodynamics. Generating and maintaining disequilibrium in a thermodynamic variable requires the extraction of power from another thermodynamic gradient, and the second law of thermodynamics imposes fundamental limits on how much power can be extracted. With this approach and associated limits, I show that the ability of abiotic processes to generate geochemical free energy that can be used to transform the surface-atmosphere environment is strongly limited to less than 1 TW. Photosynthetic life generates more than 200 TW by performing photochemistry, thereby substantiating the notion that a geochemical composition far from equilibrium can be a sign for strong biotic activity. Present-day free energy consumption by human activity in the form of industrial activity and human appropriated net primary productivity is of the order of 50 TW and therefore constitutes a considerable term in the free energy budget of the planet. When aiming to predict the future of the planet, we first note that since global changes are closely related to this consumption of free energy, and the demands for free energy by human activity are anticipated to increase substantially in the future, the central question in the context of predicting future global change is then how human free energy demands can increase sustainably without negatively impacting the ability of the Earth system to generate free energy. This question could be evaluated with climate models, and the potential deficiencies in these models to adequately represent the thermodynamics of the Earth system are discussed. Then, I illustrate the implications of this thermodynamic perspective by discussing the forms of renewable energy and planetary engineering that would enhance the overall free energy generation and, thereby 'empower' the future of the planet.

Comparative metatranscriptomics identifies molecular bases for the physiological responses of phytoplankton to varying iron availability

In vast expanses of the oceans, growth of large phytoplankton such as diatoms is limited by iron availability. Diatoms respond almost immediately to the delivery of iron and rapidly compose the majority of phytoplankton biomass. The molecular bases underlying the subsistence of diatoms in iron-poor waters and the plankton community dynamics that follow iron resupply remain largely unknown. Here we use comparative metatranscriptomics to identify changes in gene expression associated with iron-stimulated growth of diatoms and other eukaryotic plankton. A microcosm iron-enrichment experiment using mixed-layer waters from the northeastern Pacific Ocean resulted in increased proportions of diatom transcripts and reduced proportions of transcripts from most other taxa within 98 h after iron addition. Hundreds of diatom genes were differentially expressed in the iron-enriched community compared with the iron-limited community; transcripts of diatom genes required for synthesis of photosynthesis and chlorophyll components, nitrate assimilation and the urea cycle, and synthesis of carbohydrate storage compounds were significantly overrepresented. Transcripts of genes encoding rhodopsins in eukaryotic phytoplankton were significantly underrepresented following iron enrichment, suggesting rhodopsins help cells cope with low-iron conditions. Oceanic diatoms appear to display a distinctive transcriptional response to iron enrichment that allows chemical reduction of available nitrogen and carbon sources along with a continued dependence on iron-free photosynthetic proteins rather than substituting for iron-containing functional equivalents present within their gene repertoire. This ability of diatoms to divert their newly acquired iron toward nitrate assimilation may underlie why diatoms consistently dominate iron enrichments in high-nitrate, low-chlorophyll regions.

'Geoengineering'--taking control of our planet's climate

There is international consensus that 'dangerous' climate change must be avoided. Yet without radical changes in energy sources and usage and global economies, changes that so far society has been unable or unwilling to make, it seems highly likely that we will start to experience unacceptably damaging and/or societally disruptive global environmental change later this century. What actions can be taken to safeguard future environmental quality, ecosystems, agriculture, economy, and society? A new science--'geoengineering'--that until recently would have seemed pure science fiction, promises an alternative way of temporarily regaining control of climate. Colossal engineering schemes to shade the sun, make the atmosphere hazier, modify clouds, even throw iron into the ocean, are all being promoted as possible ways out of our dilemma. This article considers the state of this new science, and its implications for society.

Transient climate-carbon simulations of planetary geoengineering

Geoengineering (the intentional modification of Earth's climate) has been proposed as a means of reducing CO2-induced climate warming while greenhouse gas emissions continue. Most proposals involve managing incoming solar radiation such that future greenhouse gas forcing is counteracted by reduced solar forcing. In this study, we assess the transient climate response to geoengineering under a business-as-usual CO2 emissions scenario by using an intermediate-complexity global climate model that includes an interactive carbon cycle. We find that the climate system responds quickly to artificially reduced insolation; hence, there may be little cost to delaying the deployment of geoengineering strategies until such a time as "dangerous" climate change is imminent. Spatial temperature patterns in the geoengineered simulation are comparable with preindustrial temperatures, although this is not true for precipitation. Carbon sinks in the model increase in response to geoengineering. Because geoengineering acts to mask climate warming, there is a direct CO2-driven increase in carbon uptake without an offsetting temperature-driven suppression of carbon sinks. However, this strengthening of carbon sinks, combined with the potential for rapid climate adjustment to changes in solar forcing, leads to serious consequences should geoengineering fail or be stopped abruptly. Such a scenario could lead to very rapid climate change, with warming rates up to 20 times greater than present-day rates. This warming rebound would be larger and more sustained should climate sensitivity prove to be higher than expected. Thus, employing geoengineering schemes with continued carbon emissions could lead to severe risks for the global climate system.