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The prisoner’s dilemma is famous for boiling down the conundrum of why two perfectly rational individuals – rational, that is, other than having committed the crimes that put them in this situation in the first place – act selfishly and tell on each other, even though cooperating would be better for them as a whole.²⁵ Each player acts in their self-interest, given the circumstances. Both end up worse off as a result. It’s a simple manifestation of the free-rider phenomenon governing CO₂ emissions cuts.

Game theory is stock full of many more such dilemmas. Many attempt to capture the world in simple 2×2 matrices involving payoffs for various actions, some more contrived than others. (Game theory, of course, is not alone. See “Trolley Problem.”)²⁶ Despite some very real limitations, these thought experiments are often useful and instructive, explaining much broader points without all the verbiage. Bear with me. We will use the same logic throughout the rest of this chapter to try to understand the broader climate-policy dynamics at work.

The desire to cut CO₂ emissions, or the lack thereof, can be summarized in a simple 2×2 matrix, as shown in Table 1.1.

In the table, bold letters with subscripts represent the moves, letters without subscripts represent the outcomes. It would be a bold move to claim that this table represents all of climate policy, but it does boil down some of the most important logic to its bare essentials. H implies high mitigation, L low. The outcome is simple: Unless both players agree to want H, the outcome will be L.

Table 1.1. Climate mitigation policy as a result of players’ preferred moves: A high-mitigation agreement (H) is only possible if both players choose H over low (L) mitigation.27

Moves by players 1 \ 2	H2	L2
H1	H	L
L1	L	L

Technically, Table 1.1 represents a weakest-link negotiation game. It’s the simplest possible way to show why getting to H is so difficult: Why should one nation, state, or other jurisdiction do more than the rest, if the rest will just stick to doing L?²⁸ While the logic encapsulated in this very question demonstrates the collective-action problem at the core of climate policy, it also immediately shows some pathways to try to overcome this situation. Indeed, books have been written on just that subject. Scott Barrett’s Why Cooperate? is a good place to start.²⁹

First, cutting CO₂ emissions may not be as costly as often assumed.³⁰ Solar photovoltaic costs alone, for example, have famously declined by around 90% in the past decade alone. That might, in fact, be the most important caveat to our game here, and a hopeful one at that. Much of the delay in climate action, after all, may not be because of the lack of international coordination but because of domestic political obstacles.³¹ There, too, of course, solar geoengineering might play a role, invoking a type of moral hazard, or its inverse (see Chapter 7), though that’s not the type of interaction modeled here.

Another important caveat is that it may indeed be in some countries’ self-interest to pursue more ambitious policies around cutting CO₂ in order to persuade others to do the same. That might happen through traditional channels around carbon pricing policies.³² It might also happen via supply-side channels, for example China wanting to dominate the market for carbon mitigation technologies, thus moving the energy world from one being dominated by “petrostates” to “electrostates.”³³

If we do take the climate mitigation game as a given, however, solar geoengineering might add a particular wrinkle to these discussions. Assume that each country has one additional move: G. That option is both fast and cheap. Yes, it’s highly imperfect, too, but the first two properties alone might lead G to sweep the board. Table 1.2 shows the seemingly inevitable outcome.

The free-driver effect, in short, doesn’t ask if solar geoengineering might one day be used. It points to it simply being a question of when. Table 1.2 shows the scariest of possible outcomes: solar geoengineering not just being used in addition to ambitious CO₂ emissions cuts, but possibly even instead of them. A little bit of tradeoff between G and H might well be rational and all-but inevitable in its own right. A total substitution surely is neither rational nor inevitable. Then there’s a potentially more consequential twist.

Table 1.2. Climate policy with a solar geoengineering (G) option. Without G, low mitigation (L) dominates high mitigation (H). G dominates both.34

Moves by players 1 \ 2	H 2	L 2	G 2
H 1	H	L	G
L 1	L	L	G
G 1	G	G	G