From "the Climate Club" by William Nordhaus In Foreign AffairsMagazine this month

Even before the United States withdrew, it was clear that the national targets in the Paris accord were inconsistent with the two-degree temperature target. The accord has two major structural defects: it is uncoordinated, and it is voluntary. It is uncoordinated in the sense that its policies, if undertaken, would not limit climate change to the target of two degrees. And it is voluntary because there are no penalties if countries withdraw or fail to meet their commitments.…

A treaty focusing on an international target carbon price would not mandate a particular national policy. Countries could use carbon taxes (which would easily solve the problem of setting the price) or a cap-and-trade mechanism (such as is used by the European Union). Either can achieve the minimum price, but different countries might find one or the other approach more suited to its institutions.

Some form of sanction on nonparticipants is required to induce countries to participate in and abide by agreements with local costs but diffuse benefits. Without penalties, the agreement will dissolve into ineffectiveness, as have the Kyoto and Paris schemes.

Although many different penalties might be considered, the simplest and most effective would be tariffs on imports from nonparticipants into club member states. With penalty tariffs on nonparticipants, the Climate Club would create a situation in which countries acting in their self-interest would choose to enter the club and undertake ambitious emission reductions because of the structure of the payoffs.

One brand of penalty could be a countervailing duty on the carbon content of imports. However, this approach would be both complicated and ineffective as an incentive to join a club. The main problem is that much carbon dioxide is emitted in the production of nontraded goods, such as electricity.

 A second and more promising approach would be a uniform tariff on all imports from nonclub countries into the club. Take as an example a penalty tariff of five percent. If nonparticipant Country A exported $100 billion worth of goods into the club countries, it would be penalized with $5 billion of tariffs. The advantage of uniform tariffs over countervailing duties is simply simplicity. The point is not to fine-tune the tariffs to a nonparticipant country’s production structure but to e powerful incentives for countries to be part of the Climate Club.

Modeling offers insights rather than single-digit accuracy. The basic lesson is that current approaches are based on a flawed concept of how to manage the global commons. The voluntary approach needs to be replaced by a club structure in which there are penalties for nonparticipation—in effect, environmental taxes on those who are violating the global commons. 

The international community is a long way from adopting a Climate Club or a similar arrangement to slow the ominous march of climate change. The obstacles include ignorance, the distortions of democracy by anti-environmental interests, free-riding among those looking to the interests of their country, and shortsightedness among those who discount the interests of the future. Although this is a radical proposal that breaks with the approach of past climate negotiations, no other blueprint on the public agenda holds the promise of strong and coordinated international action.