Whose climate intervention? Solar geoengineering, fractions of capital, and hegemonic strategy

Proposals for slowing climate change by reflecting sunlight back to space, known as solar geoengineering (SG), are gaining traction in climate policy. Given SG’s capacity to slow warming without reducing carbon emissions, prominent criticism suggests that it will enable fossil fueled business-as-usual. This assessment is not without merit, yet the primary funders of SG research do not emanate from fossil capital. We analyze sources of funding for SG research, finding close ties to financial and technological capital as well as a number of billionaire philanthropists. These corporate sectors and associated philanthropies comprise part of “climate capital” – the fraction of the capitalist class aligned with climate action. We argue that SG is being positioned as a tactic for enabling incremental, market-driven decarbonization, explore key institutions advocating this approach in US climate policy, and conclude that SG is poised to serve as a tool for class compromise between fossil and climate capital.

How can solar geoengineering and mitigation be combined under climate targets?

So far, scientific analyses have mainly focused on the pros and cons of solar geoengineering or solar radiation management (SRM) as a climate policy option in mere isolation. Here, we put SRM into the context of mitigation by a strictly temperature-target-based approach. As the main innovation, we present a scheme that extends the applicability regime of temperature targets from mitigation-only to SRM-mitigation analyses. We explicitly account for one major category of side effects of SRM while minimizing economic costs for complying with the 2 ∘C temperature target. To do so, we suggest regional precipitation guardrails that are compatible with the 2 ∘C target. Our analysis shows that the value system enshrined in the 2 ∘C target leads to an elimination of most of the SRM from the policy scenario if a transgression of environmental targets is confined to 1/10 of the standard deviation of natural variability. Correspondingly, about half to nearly two-thirds of mitigation costs could be saved, depending on the relaxation of the precipitation criterion. In addition, assuming a climate sensitivity of 3 ∘C or more, in case of a delayed enough policy, a modest admixture of SRM to the policy portfolio might provide debatable trade-offs compared to a mitigation-only future. Also, in our analysis which abstains from a utilization of negative emissions technologies, for climate sensitivities higher than 4 ∘C, SRM will be an unavoidable policy tool to comply with the temperature targets. The economic numbers we present must be interpreted as upper bounds in the sense that cost-lowering effects by including negative emissions technologies are absent. However, with an additional climate policy option such as carbon dioxide removal present, the role of SRM would be even more limited. Hence, our results, pointing to a limited role of SRM in a situation of immediate implementation of a climate policy, are robust in that regard. This limitation would be enhanced if further side effects of SRM are taken into account in a target-based integrated assessment of SRM.

Impacts of three types of solar geoengineering on the North Atlantic Meridional Overturning Circulation

Climate models simulate lower rates of North Atlantic heat transport under greenhouse gas climates than at present due to a reduction in the strength of the North Atlantic meridional overturning circulation (AMOC). Solar geoengineering whereby surface temperatures are cooled by reduction of incoming shortwave radiation may be expected to ameliorate this effect. We investigate this using six Earth System Models running scenarios from GeoMIP (Geoengineering model intercomparison project) in the cases of: i) reduction in the solar constant, mimicking dimming of the sun; ii) sulfate aerosol injection into the lower equatorial stratosphere; and iii) brightening of the ocean regions mimicking enhancing tropospheric cloud amounts. We find that despite across model differences, AMOC decreases are attributable to reduced air-ocean temperature differences, and reduced September Arctic sea ice extent, with no significant impact from changing surface winds or precipitation-evaporation. Reversing the surface freshening of the North Atlantic overturning regions caused by decreased summer sea ice sea helps to promote AMOC. Comparing the geoengineering types after normalizing them for the differences in top of atmosphere radiative forcing, we find that solar dimming is more effective than either marine cloud brightening or stratospheric aerosol injection.

The Controversial One

This chapter considers solar radiation management, also known as solar geoengineering, which seeks to manipulate Earth’s climate energy balance by reducing the absorption of incoming solar energy. As the chapter explains, this approach spans a class of proposed measures that has been polarizing the community, with some advocating it as an essential means of keeping global warming within acceptable limits, while others see only grave drawbacks and dangers. The chapter describes the two approaches to limiting the absorption of solar energy: measures taken in space, between Earth and the Sun, to reflect or disperse solar radiation before it even hits Earth’s atmosphere; and measures taken in Earth’s atmosphere or at the Earth’s surface to reflect incoming solar radiation. It goes on to discuss the various proposed methods, their potential, and their drawbacks.