Virtually all of the energy at the surface of the Earth comes to us from the Sun. This is the energy that, in combination with the greenhouse gases in the atmosphere, maintains our current surface temperature in the range where liquid water is present. In this chapter we will examine solar radiant energy, and its most important interactions with the various constituents of the Earth’s atmosphere. Most of it reaches the lower troposphere, some to be absorbed by water vapour, and some to be scattered by clouds, molecules, or aerosols. The rest (roughly half) reaches the ground. Human activity has the power to alter these inflows, in a number of ways. We devote one section to the potentially disastrous Nuclear Winter scenario, and another to the potentially useful idea, known as Geoengineering, of reflecting some of the incoming sunlight in order to re-balance the Earth’s energy budget.

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.

As I indicated in the Introduction, I will begin my tour of four select security referents at the macro level and work my way down. I will do so for four reasons. The first is to help shake off any lingering anthropocentric biases that might skew the analysis were we to work in the opposite direction. Human security, of course, naturally invites an anthropocentric treatment; culture as I shall be discussing it is also largely a human concern; and the state is a human creation. Were we to get into the habit of putting people at the centre of our analysis, we might do so too readily precisely where it would be least appropriate. The second is that ecospheric security will be the least familiar concept of the four and for that reason might risk coming across as an afterthought if I were to treat it last. Third, and relatedly, given the unfamiliar style of analysis to which I aim to subject these referents, I see advantages in giving it its first rigorous test in a context in which it is least likely to grate, hoping thereby to cultivate a degree of comfort with it once I turn to referents that we are used to analyzing in less unconventional ways. Fourth, and most importantly, I will argue that the ecosphere must take priority as a security referent, and accordingly must condition our understanding of the others. This argument would be more difficult to make were I to put various carts before the horse.