Mancur Olson offered us big thoughts on big subjects. Today, he might well attack the problem of climate change and the current failure of nations to act effectively. Olson would note the incentives of nations to ride free or cheaply. He would observe that climate change is an alliance problem, one where some nations have much more at stake than others. With climate change, the alliance problem is redoubled, since the asymmetries among nations fall along multiple dimensions, including those of vulnerability to climate change, history of greenhouse emissions, emissions per dollar of GNP, level of economic development, and cultural environmental concerns. Each nation, valuing primarily its own concerns, advances principles favoring itself in the apportionment of painful cuts. Not surprisingly, the cuts that nations have agreed upon for the heralded 2015 Paris Accords will be woefully insuffi cient to avoid exacerbating climate change. Thus, despite much international discussion and many platitudinous agreements, concerns about the distribution of painful cuts will continue to prevent the nations of the world from even approaching an effi cient agreement. Our threatened planet needs a more sophisticated approach to this and other collective action problems, a fi eld pioneered by Mancur Olson.