Chapter 5 addresses the potential use of climate engineering technologies as a way of counteracting anthropogenic global warming. These technologies encompass methods for the permanent removal of atmospheric carbon dioxide, for instance via its direct capture from ambient air and subsequent geological storage. They also include more controversial technologies that would modify the planetary albedo in order to reflect a small fraction of incoming sunlight back into space in order to induce an artificial cooling effect. These two sets of technologies play out against the background of the increasingly dim prospects of achieving international temperature targets in line with the 2015 Paris Agreement. The chapter traces institutional responses to both negative emissions technologies and solar geoengineering across a multitude of international forums, including the Convention on Biological Diversity, the London Convention on the Dumping of Waste at Sea, and the Paris Agreement itself.

This chapter describes five “action areas” in which politically achievable changes over the coming two decades could render humankind a lot safer than it is today. For climate change, these include urgent measures for rapid decarbonization, coupled with ramped-up research on technologies for carbon removal and for solar radiation management; new international pacts among small groups of nations for emissions reductions with mutual accountability and incentives; and pre-adaptation measures for dealing effectively with unavoidable harms caused by global warming. For nuclear weapons, these include preparing contingency plans for major or limited nuclear wars, as well as risk-reduction measures than can be implemented today. For pandemics, experts point to four sensible and affordable measures that would greatly reduce the harms of future pandemics. For AI, an immediate challenge will be to prepare for chronic mass unemployment due to rising levels of automation. Finally, the chapter proposes the creation of a new federal agency, the Office for Emerging Biotechnology, to oversee and regulate cutting-edge developments in this field.

In this chapter we leap over the divider in our geoengineering toolbox to examine the implements on the other side of our portfolio by considering several prospective solar radiation management techniques. These begin with surface modifications that might in some way increase the albedo of the earth and cause it to absorb less solar energy, including lightening roofs and other built structures, bioengineering crops to be slightly lighter, and manipulating ice to reflect more sunlight. Glaciers could be reinforced to slow their slides into the sea. Turning our gaze upward, marine cloud brightening is a technique that could increase the reflectivity of clouds, while cirrus cloud thinning could reduce the heat-trapping effect of these high wispy clouds. Yet higher up, it may someday be possible to deploy assets in space the might deflect some of the incoming sunlight. However, the surface modification techniques don’t appear to be properly scaled to the problem, and the cloud and space-based ideas remain too speculative to rely upon.

Geoengineering describes a range of technologies that attempt to mitigate the effects of global warming caused by increasing greenhouse gas concentrations. Some geoengineering approaches remove carbon dioxide from the atmosphere. These are not controversial, but they are currently too expensive to serve as a viable option. The most cost-effective technique, called solar radiation management, aims to reflect sunlight by continuously dumping large quantities of sulfate aerosols into the stratosphere, much as a volcanic eruption would. But geoengineering attempts to address the symptoms of the disease of global warming rather than the disease itself, which will persist as long as carbon emissions continue. Computer models of climate are essential to assess the efficacy of any geoengineering approach, because large-scale physical experimentation would be dangerous. However, the information that is most crucial for us to know – the impact geoengineering would have on regional climates – is something models have trouble predicting.

This chapter debates the consistency of the deployment of Solar Radiation Management (SRM) with international law. SRM might help to counter global warming at relatively low cost, but it could also have substantial negative environmental impacts. Jesse Reynolds, reviewing all the relevant international treaties, as well as customary international law, argues that solar geoengineering could be consistent with international law. There is even some evidence, he argues, that solar geoengineering may be required by international law. Kerryn Brent reaches the exact opposite conclusion. She argues that solar geoengineering at scale would violate the no-harm rule and is prohibited by the UNFCCC and other treaties.

This chapter debates the consistency of the deployment of Solar Radiation Management (SRM) with international law. SRM might help to counter global warming at relatively low cost, but it could also have substantial negative environmental impacts. Jesse Reynolds, reviewing all the relevant international treaties, as well as customary international law, argues that solar geoengineering could be consistent with international law. There is even some evidence, he argues, that solar geoengineering may be required by international law. Kerryn Brent reaches the exact opposite conclusion. She argues that solar geoengineering at scale would violate the no-harm rule and is prohibited by the UNFCCC and other treaties.