Reduction in carbon dioxide emissions constitutes a global public good; and hence there will be strong incentives for countries to free ride in the provision of CO2 emission reductions. In the absence of more or less binding international agreements, we would expect carbon emissions to be seriously excessive, and climate change problems to be unsolvable. Against this obvious general point, we observe many countries acting unilaterally to introduce carbon emission policies. That is itself an explanatory puzzle, and a source of possible hope. Both aspects are matters of ‘how politics works’ – i.e. ‘public choice’ problems are central. The object of this paper is to explain the phenomenon of unilateral policy action and to evaluate the grounds for ‘hope’. One aspect of the explanation lies in the construction of policy instruments that redistribute strategically in favour of relevant interests. Another is the ‘expressive’ nature of voting and the expressive value of environmental concerns. Both elements – elite interests and popular (expressive) opinion – are quasi-constraints on politically viable policy. However, the nature of expressive concerns is such that significant reductions in real GDP are probably not sustainable in the long term – which suggests that much of the CO2 reduction action will be limited to modest reductions of a largely token character. In that sense, the grounds for hope are, although not non-existent, decidedly thin.