Читать книгу Geoengineering - Gernot Wagner - Страница 20

As a rule, there’s little use in introducing game theory, if it doesn’t lead to some seemingly counterintuitive results. The 2×2 matrix here might show why climate mitigation action is hard, but that’s about it. It doesn’t point to any solutions to the dilemma. The 3×3 matrix, with G for solar geoengineering, does the same. It shows how G will dominate, nothing more. There’s no more guidance other than to say that everyone should just agree to cut CO₂ considerably – pick H – and get on with it.

Failing to act on cutting CO₂ emissions – picking L – is scary for the planet as a whole. Slithering into solar geoengineering might be scarier still. With that setup, and with a bit more work to understand what’s behind Table 1.2, there may well be a way out of this dilemma.

Focusing on H, L, and G alone has lots of limitations. That’s for sure. But sticking with that logic for a bit longer, let’s try to rank countries’ preferences once again. There are those ranking H ≻ L. (Read the squiggly “≻” simply as saying “preferred to.” No other magic there.) That implies large climate concern, at least larger than those not ranking H first. It might also imply that, for this particular player, cutting CO₂ is relatively cheap, again at least relatively speaking. Either way, this player would clearly prefer H.

For those ranking H ≻ L, there are now three options for where G could go: first, second, or third. First implies that G dwarfs all else: G ≻ H ≻ L. That ranking would be bad, for at least two reasons. First, solar geoengineering would win, to the exclusion of any other climate policy; clearly a bad outcome. It also makes the game-theoretic model moot. No need for a 3×3 matrix, the outcome is clear: G wins, unless, for example, nations agree on a strict, enforceable moratorium (see Chapter 8).

G going third, H ≻ L ≻ G, is similarly boring. Now even the low-mitigation scenario is preferred to any solar geoengineering use. That’s clearly a possible preference ranking. The more fundamentalist elements of the German Green Party come to mind. They might prefer H to L and, thus, abhor anything that appears like a technofix to the much larger, structural problems of the current fossil-fuel economy. I call this position “boring” not because the position itself is. Far from it. It calls for a radical reorganization of society as we know it. But it does now mean G is sidelined in favor of an exclusive focus on cutting CO₂ emissions.

A third possible ranking is H ≻ G ≻ L, one that ranks G second, possibly far behind H but still (reluctantly or not) above L. Even, or perhaps especially, ardent environmentalists might support this ranking in a fit of desperation, given how far unchecked climate change has proceeded.

As in any game-theoretic setting, a good deal now depends on what the other player does. There, too, are three possibilities. We already know that this player ranks L ≻ H. Once again, G can either go first, second, or third.

With G first, we already know what will happen. Ranking G ≻ L ≻ H yields the same outcome as the other player G ≻ H ≻ L. G dominates. Once again, the only way to prevent solar geoengineering in this scenario is to attempt to ban it: a global moratorium of sorts (see Chapter 8).

What, then, if G is ranked second, implying L ≻ G ≻ H for this player. This now quickly gets more complicated, though not prohibitively so. Table 1.3 shows the complete picture.

Table 1.3. Climate outcomes based on each player’s complete preferences. Availability of geoengineering (G) could lead to high mitigation agreement (H, in bold), despite one player preferring low mitigation (L) to H.35

1 \ 2	H ≻ L ≻ G	H ≻ G ≻ L	L ≻ G ≻ H	L ≻ H ≻ G	G ≻ L ≻ H	G ≻ H ≻ L
H ≻ L ≻ G	H	H	L	L	G	G
H ≻ G ≻ L	H	H	G	H	G	G
L ≻ G ≻ H	L	G	L	L	G	G
L ≻ H ≻ G	L	H	L	L	G	G
G ≻ L ≻ H	G	G	G	G	G	G
G ≻ H ≻ L	G	G	G	G	G	G

In Table 1.3, go to the third row, which has “L ≻ G ≻ H” as player 1’s preference. The only outcomes are L and G:

1 \ 2	H ≻ L ≻ G	H ≻ G ≻ L	L ≻ G ≻ H	L ≻ H ≻ G	G ≻ L ≻ H	G ≻ H ≻ L
L ≻ G ≻ H	L	G	L	L	G	G

Which one it is depends entirely on whether player 2 prefers L ≻ G or G ≻ L, regardless of how they rank H.

The big question is why the player preferring L to H might rank L ≻ G ≻ H. If this player ranks L ≻ H strictly because of costs of cutting CO₂ emissions, L ≻ G ≻ H will be a very real possibility. G, after all, is cheap. We are immediately back to the moratorium, assuming the world doesn’t want G to win it all. Ban it, and hope to guide climate policy in a productive direction – toward H, that is.

If that player, however, ranks L ≻ H because they do not believe climate change is a problem worth addressing with aggressive action, L ≻ G ≻ H will be less likely. Why risk G if climate change isn’t all that bad to begin with?

Now we are in the third scenario: L ≻ H ≻ G. Zoom into the fourth row of Table 1.3 to see where this might lead:

1 \ 2	H ≻ L ≻ G	H ≻ G ≻ L	L ≻ G ≻ H	L ≻ H ≻ G	G ≻ L ≻ H	G ≻ H ≻ L
L ≻ H ≻ G	L	H	L	L	G	G

The most frequent outcomes are still L and G. If the other player ranks G on top, G wins. Not if, but when. What’s striking, then, is when G does not win. That seemingly goes counter to the “not if, but when” logic.

Let’s simplify the table a bit more to see this logic. We can drop the two columns where G is ranked first, and compare the first four columns for when L ≻ H ≻ G (row four of Table 1.3) to the ones when L ≻ G ≻ H (row three):

1 \ 2	H ≻ L ≻ G	H ≻ G ≻ L	L ≻ G ≻ H	L ≻ H ≻ G
L ≻ G ≻ H	L	G	L	L
L ≻ H ≻ G	L	H	L	L

If both players rank L on top, L wins. G doesn’t add much to this calculus. Let’s drop two more columns, to compare players ranking L first to those ranking H first. Now we’re left with exactly four cases:

1 \ 2	H ≻ L ≻ G	H ≻ G ≻ L
L ≻ G ≻ H	L	G
L ≻ H ≻ G	L	H

The first column has two cases leading to L as the outcome. That’s when the player ranking H ≻ L also ranks G last. The game essentially collapses to the prisoner’s dilemma of yore. G doesn’t influence the decision. L wins.

Almost there. We’re left with two cases.

With G wedged between L and H for both players, G wins. In some sense, the logic here is simply that the two players can’t agree on how much CO₂ to cut, so they would rather settle on G than give the other player what they want in terms of CO₂ cuts. That’s a disheartening solution. It’s also the one that calls for strong solar geoengineering governance. But it’s not the only solution.

If G is ranked below H for those preferring L to H, suddenly, H emerges as the winner. That’s true, even though one player still ranks L ≻ H. Here the “availability of risky [solar] geoengineering can make an ambitious climate mitigation agreement more likely.” That, in fact, is the title of the paper I wrote with then-Ph.D. student Adrien Fabre, arguing just that.³⁶ The title of that paper is worth restating: it’s the mere availability of solar geoengineering that leads to this outcome. Another key word: “risky.” In fact, the riskier is solar geoengineering, the more likely is this outcome.

That mere availability helps break the prisoner’s dilemma, the free-rider problem. It isn’t a guarantee. But the mere possibility is worth pointing out: If G ranks just below H for either player, G might indeed help induce H. That’s true even though one player still ranks L ≻ H. Assuming G is not just fast and cheap but also highly imperfect – even those ranking L ≻ H still prefer H to G, putting it last – the mere availability of G might prompt otherwise quarreling parties to opt for H.

All of that is true despite our setup that rigged things against H in the first place. Recall how the weakest-link game setup in Table 1.1 all but guaranteed that L would win.

Enter G, and L is no longer a given. The most likely case with G as an option might still be for G to take all: Somebody, somewhere, will opt to use G, and it will dominate the final outcome. All of that seems to put the burden squarely on governments to rein in tendencies to do too much, too soon – in less-than-ideal ways. (Part III will explore the urgent need for governance in more detail.)

Meanwhile, as long as G is sufficiently risky and uncertain, it might indeed help to induce H. Solar geoengineering, done sensibly, may be a net positive for the planet, or it might not be. We don’t yet know enough. The operative terms here are “risky and uncertain.” Solar geoengineering is both. There are lots of ways in which things could go off the rails.