numbers, not adjectives — D. J. C. MacKay

Climate Change Cooperation

Carl Edward Rasmussen

June 20, 2026

In the long history of humankind, those who learned to
collaborate and improvise most effectively have prevailed.
— after Charles Darwin

The Themis Mechanism

Climate change is a serious problem, but not an intractable one. What is missing is not technology, political will, or moral commitment – but structure: an agreement designed so that cooperation is the rational choice, built on well-understood mechanisms, and consistent with nations pursuing their own interests. The Themis Mechanism is that structure – and the pages below explain why, given the nature of the problem, it can hardly take any other form.

The structure of our climate crisis

When we emit greenhouse gases, we are using a shared resource without paying for it. This is what economists call an unpriced externality: a cost imposed on others that is not reflected in the price of the activity that causes it. When a resource is treated as free, it tends to be overexploited. The atmosphere is no exception.

Humans are great cooperators, and our sophisticated societies would not be possible otherwise. But we struggle to apply these very same principles at the global scale. The political economist Elinor Ostrom in her book “Governing the Commons”, uncovered the principles of how communities cooperate in the real world: by binding commitments, reciprocity, mutual trust, transparency, and enforceable sanctions. Themis is designed around precisely these principles.

We can develop cheaper solar panels, better batteries, and more efficient carbon capture – and we should. But technological progress does not by itself resolve the question of who is entitled to use our shared atmospheric resources, and on what terms. As long as emissions remain unpriced, the incentive to overuse persists.

This matters even if renewables continue to fall in cost. We do not yet know whether that will happen at the required scale and speed. If it does, then pricing emissions will do no harm – carbon pricing becomes unimportant, a mechanism quietly made redundant by the very progress it helped incentivise. If not, then pricing will help to prevent catastrophe. The cost of having the mechanism in place when it turns out not to be needed is negligible. The cost of not having it when it turns out to be needed is not. This asymmetry is decisive.

A country with one percent of the world’s population that invests in emission reductions captures roughly one percent of the climate benefit – the other ninety-nine percent spills over to the rest of the world. Acting alone is economically irrational, and the incentive to wait for others becomes overwhelming. A coalition changes this arithmetic entirely. If nations responsible for half of global emissions act together, each member’s spillover becomes every other member’s climate return. The national payoff is roughly fifty times larger than with unilateral action – at no additional cost. This is not a marginal improvement. It is the difference between a structure in which acting is economically irrational and one in which cooperation pays off.

The problem is therefore not primarily one of technology, or political will, or individual virtue – though these matter too. It is principally structural: cooperation is required, and cooperation of this kind means binding agreements. Without binding commitments, agreements remain fragile, discouraging the very action they are meant to enable. Nations can and will enter such agreements – not out of altruism, but because, if they value the conditions of future generations, it is in their interest to do so. Once the nature of the problem is understood, the solution follows from the structure of the problem itself.

Conditional common commitments – “I will if you will”

Unconditional national pledges – however sincere – are not cooperation in any meaningful sense: effective cooperation requires that each party’s commitment be conditional on the commitment of others. Cooperation becomes the rational choice, not a gamble on others’ goodwill.

A common objection is that nations are too self-interested for binding commitments. But this mistakes the nature of the problem. If nations act in their self-interest – and they do – the task is not to appeal to their better nature. It is to design an agreement in which cooperation is the self-interested choice. Climate change is not a zero-sum game. As the arithmetic of the previous section showed, within a coalition, a nation’s climate investments pay back fifty-fold compared to acting alone. National self-interest and global benefit are not opposed; they can be aligned. Cooperation has nothing to do with altruism. It is how national self-interest gets served.

Why must commitments be common – the same for all? Not as an ideological preference, but as a practical necessity. One hundred and ninety-seven nations cannot reach agreement on individually bespoke deals; uniform terms are the only terms negotiable at this scale. The prevailing framework – “common but differentiated responsibilities” (CBDR), enshrined in UN climate negotiations – sounds principled, but is structurally the opposite of common commitments: each nation defines its own obligations, which remain vague, incomparable, and perpetually open to reinterpretation. Common commitments and CBDR do not differ in degree; they point in opposite directions. Equity under Themis is achieved not by differentiating the rules, but by pairing common rules with a transfer that reflects unequal per-capita use of the atmosphere. Equal rights and responsibilities per capita is the only baseline that is both ethically defensible and practically actionable.

Common conditional commitments are what “I will if you will” means precisely. Not a moral appeal, not a loose aspiration – a structural design in which cooperation is self-reinforcing because defection carries a cost. Any agreement that lacks these properties simply replicates structures which have failed for decades.

What common commitments must look like

Common commitments must be equitable across a wide range of national conditions. This is addressed through two components acting together: international transfer and nationally retained minimum price.

The ethical foundation is the international transfer. When you use a shared resource, you pay for what you use – and since the atmosphere belongs to everyone equally, the payment is distributed equally per capita. Nations with above-average per-capita emissions pay into a common pool; nations with below-average per-capita emissions receive from it. The logic is universal: simple, principled, and independent of development status. Applied domestically, this structure is known as carbon fee and dividend – a carbon price whose revenue is returned equally to all residents. Themis applies the same principle at the international level, between nations rather than between individuals.

On its own the transfer creates a problem of political viability. A high price means wealthy high-emitting nations hand over large sums – politically untenable, even if just. Therefore the agreed price would remain modest, and the environmental impact small. This is why Themis pairs the transfer with a nationally retained carbon price: every participating nation commits to pricing emissions at or above a common floor, and keeps the revenue entirely. Higher prices become acceptable to wealthy nations because the money stays at home; lower-emitting nations can accept a high domestic price because the transfer is on the table. Together, the two components make an ambitious price politically achievable across the full spectrum of participating nations. This is pragmatic, not compromised: a mechanism too pure to attract participation achieves nothing.

A global carbon price is simpler and more robust than a global cap-and-trade scheme. Any fair distribution of allowances would have to be per-capita which recreates the same political problem as a pure international transfer: wealthy nations buying allowances from poorer ones at scale is politically untenable at ambitious prices, with no obvious equivalent of the nationally retained price to compensate. A price floor avoids this entirely and is straightforward to verify. Domestically, nations are free to use whatever instruments they choose – carbon taxes, cap-and-trade, efficiency standards, or any combination – provided the effective price meets the common floor. Themis partners care about the price, not the method.

The design dissolves several common objections. A carbon price sounds regressive – a burden falling disproportionately on poorer households and poorer nations. But the per-capita transfer inverts this at the international level: the mechanism as a whole redistributes from high-emitting wealthy nations to lower-emitting less wealthy ones. Equally, whether nationally retained pricing is regressive depends entirely on how these revenues are utilised. There is nothing inherently regressive in Themis. Themis does not address historical emissions. Participating in Themis does not absolve nations of responsibility for their past; a separate mechanism must be devised.

The two-pronged pricing structure is not one design among several: it is the only form that is simultaneously common, equitable, and politically viable at an emissions price high enough to matter.

Reaching agreement

The Themis Mechanism has two operational components: a coalition implementing conditional common commitments, and an elicitation process for agreeing the governing quantities – the domestic carbon price and the international transfers. It operates on an annual cycle.

The coalition is not a universal treaty requiring unanimous consent. The UN model sets the bar at the level of the least ambitious participant – a structural guarantee of inadequacy. Themis operates differently: nations that choose to join do so; others do not. A coalition of this kind is what the economist William Nordhaus calls a “climate club” – the key insight being that progress need not wait for unanimity. Progress is not held hostage to the most reluctant actor, and the coalition can grow as the case for joining becomes harder to resist. Free-riders – those who benefit from members’ emission reductions without contributing – cannot be prevented entirely, but they must face consequences. Free-riding must be sanctioned.

Agreeing on the governing quantities might seem to require a vote. But a democratic vote assumes that everyone who votes is then bound by the outcome – inappropriate for sovereign nations who cannot be compelled. Instead, Themis uses an elicitation process: each nation submits its preferences for the governing quantities; these are synthesised into a set of governing values using a procedure that is open, transparent and fully specified in advance; nations then decide independently whether to join the coalition for that year at those governing values. Nations never commit to anything long-term, and never agree to anything not fully specified.

This annual cycle is not merely administrative. It allows the mechanism to adapt to changing circumstances – new science, new technologies, shifting economics, evolving geopolitics – and it provides ongoing assurance that partners honour their commitments. Trust is not assumed; it is built through repeated, verifiable, annual decisions. This is what a functioning mechanism looks like – unlike aspiration without structure.

What becomes possible

None of what has been described above requires innovation in human nature. The mechanisms are well understood; the arithmetic is straightforward; the ethical foundation is sound. No nation is asked to go first: because commitments are common and conditional, joining carries no risk of exploitation.

The mechanism is specified in sufficient detail to be implemented. What it requires now is engagement: from policymakers who can carry it into practice, from researchers who can test and refine it, from communicators who can explain why the existing framework has been deficient and what a structural alternative looks like.

The world in which Themis operates is not a world transformed by sacrifice. It is a world in which every ton of emissions carries a price and every annual cycle builds mutual trust. Not utopia. A structure in which self-interest is no longer the obstacle – but the engine.

The climate problem is serious. The solution is available. The question is whether enough people understand it clearly enough to act.

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