The article explores why countries might join efforts to reduce carbon emissions on a smaller scale. By using a model that considers both the costs and benefits of cutting emissions, the researchers found that larger regions like the U.S. have strong incentives to reduce emissions, even without full global participation. When regions work together to cut emissions, the benefits increase, especially for energy importers. However, cutting emissions can also affect production and consumption in other regions, so it may be necessary to impose limits on non-participants for these efforts to be successful. Overall, even with limited participation, reducing emissions can still be beneficial for countries involved.