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

Climate Change Cooperation

Carl Edward Rasmussen

July 17, 2026

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

The Themis Mechanism

How can we dramatically improve the effectiveness of our climate change approach – without replacing the Paris Agreement?

What could be strengthened?

Reducing emissions costs money. The question is whether the return justifies the cost. When a nation reduces its emissions, the climate benefit is shared globally. A country responsible for eg 1% of global emissions – the UK, for example – experiences roughly 1% of the climate return from its own reductions. The other 99% manifests in other nations.

It’s not that investment in greenhouse gas reductions don’t pay off – it’s just that they mostly pay off elsewhere. This makes national climate incentives very weak.

You might object that nations have other reasons to act: cheaper renewables, energy security, cleaner air, industrial competitiveness. These co-benefits are real, and for some countries substantial. But they are unevenly distributed. And since climate change is caused by our collective behaviour, relying on mechanisms which aren’t practically universal will undermine our collective response.

Nor does falling technology cost resolve this. Even as renewables get cheaper, the incentive structure stays the same: a nation reducing emissions still “exports” most of the climate benefit. The problem is not the cost of action – it is who captures the return.

There is a structural solution. If nations make their commitments conditional – “I will if you will” – this changes everything. When a large group of nations acts on conditional commitments, they’ll each experience a large fraction of the climate benefits: effects of their own and other nation’s reductions. The climate payoff is multiplied, at no extra cost. And because the risk of acting while others don’t is removed, nations are willing to commit to far more ambitious action conditionally than they ever would unconditionally.

Conditionality is the missing ingredient. The Paris Agreement, for all it has achieved, is built entirely on unconditional unilateral pledges – each nation’s commitments stand regardless of what others do. Adding conditionality would not replace what exists; it would multiply it.

Route to agreement

Conditional commitments are compelling in principle. The practical question is how a coalition based on conditionality could actually be formed and function.

A natural starting point is unanimous membership, as in the Paris Agreement. Unanimity sounds like the fairest standard: no-one is left out, every voice counts. But it has a structural flaw. A requirement for unanimity gives every nation a veto. The nation with the least ambition can hold out, blocking any agreement more demanding than it is willing to accept. Unanimous membership is therefore not a sign of strength – it is a structural guarantee that ambition will be limited to the level of the least ambitious.

To resolve this, we need a more nuanced view of inclusivity. There is an important distinction between being heard and ultimately joining. Every nation can participate in shaping the terms of an agreement; not every nation needs to become a member. A coalition that moves forward without unanimity can grow as the case for joining becomes harder to resist. Non-members are not silenced – they simply choose to stay out.

Accepting that membership need not be unanimous raises the next question: how do members agree on what they are committing to? Free form negotiation among a large number of diverse nations is intractable. Each nation’s attempt to secure bespoke terms creates an endless tangle of competing demands – the same logic that makes unanimity unworkable makes unconstrained negotiation unworkable. The solution is a uniform, canonical framework: common commitments for all members, specified in advance. Nations do not specify the framework – they can influence the terms and decide whether to join.

Where the framework comes from matters less than what it offers. If joining serves a nation better than not joining, that is the only legitimacy required. And because the climate payoff grows with coalition size, a framework that attracts early members becomes increasingly attractive to the next – its legitimacy is not declared in advance, but built through adoption.

This sounds restrictive, but it opens rather than closes the door. Because nations are not negotiating bespoke arrangements, the framework can be designed so that joining is genuinely in the interest of a sufficient majority. This is a powerful legitimacy criterion – not unanimity, not the pretext of absolute fairness, not coercion, but self-interest. An agreement is legitimate when joining serves a nation better than not joining. And a well-designed conditional commitment framework meets this test: the climate payoff of membership greatly exceeds the payoff of standing aside.

Free-riders – nations who reap the benefit of others without contributing themselves – threaten conditional and unconditional agreements alike. But because agreements based on conditional commitments will likely be far more ambitious, free-riding may be seen as a bigger problem. A coalition cannot accept free-riding, which must be sanctioned eg through trade barriers.

A viable mechanism therefore needs exactly two components: a specification of the coalition – who is in, on what terms – and a process for arriving at those terms that preserves every nation’s voice without giving any nation a veto. The first is the coalition structure; the second is the elicitation process. These are the two components of the Themis Mechanism.

The Themis Mechanism

The preceding sections have established what is needed: a coalition of nations making conditional commitments on uniform terms, with a process that preserves every nation’s voice without giving any nation a veto. What remains is to specify what those commitments should look like.

The commitment must be the same for everyone. Emission caps cannot meet this requirement: a common cap quantity is meaningless across nations of vastly different sizes and circumstances, and any differentiated cap requires exactly the bespoke negotiation already ruled out. A minimum price on emissions is different – the same for all members, verifiable, and effective. This is the natural candidate for the common commitment.

A uniform price immediately raises a question of scope. Purely global pricing – where revenue flows into a global pool and is redistributed per capita – is equitable: nations using more than their fair share of our atmospheric resource pay; those who use less are paid. But at any ambitious price, wealthy high-emitting nations would be writing large cheques to foreign nations. This is politically untenable, and would force the agreed price down to the point of ineffectiveness.

A purely nationally retained price avoids this: each nation charges its own emissions and keeps the revenue. Politically viable – but it leaves the equity problem unsolved, and removes the financial stake that binds members to the coalition.

The solution is both together. An international transfer handles equity: nations pay or receive according to their per-capita emissions, at an internationally agreed rate. A nationally retained minimum price handles political viability: every member commits to pricing emissions at or above a common floor, and keeps that revenue entirely. Together, they make an ambitious price achievable across the full range of member nations. Neither component works without the other; together they are the only form that is simultaneously equitable, politically viable, and ambitious enough to matter.

A carbon price is sometimes said to be regressive – a burden falling disproportionately on poorer households and nations. At the international level, Themis inverts this: the transfer redistributes from wealthy high-emitting nations to less wealthy lower-emitting ones. At the national level, how retained revenue is used is each nation’s own choice – returning it equally to all residents is one progressive option.

Agreeing on the governing quantities – the transfer rate and the minimum price – cannot be left to open negotiation: that is the intractable process already ruled out. Instead, each year, every nation submits its preferred values for these quantities. These submissions are synthesised into governing values using a procedure that is fully specified, transparent, and agreed in advance. Nations then decide independently whether to join the coalition for that year at those values. No nation is bound to anything it has not chosen; no nation’s submission is ignored.

The annual cycle is not merely administrative. Trust between nations is not declared – it is built through repeated, verifiable actions. Each cycle, members confirm their commitments and observe that others have done the same. The mechanism also adapts: new science, shifting economics, and changing geopolitics are absorbed into each year’s cycle rather than requiring renegotiation of the entire agreement.

The conditional structure, the two-pronged pricing commitment, and the annual elicitation cycle together form the Themis Mechanism – a set of conditional common commitments. No nation is asked to act against its interests. No nation goes first. No nation makes an open-ended commitment – each year is a fresh decision. The coalition need not start universal; it need only start. Practicality is not a hope – it is built into the design.

The Paris Agreement established that nations can commit together to a common climate goal. Conditional common commitments add the structure that makes achieving it the rational choice. Paris and Themis together do not merely improve on what exists – they change what is possible.

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