Carbon budgets are a useful way to frame the climate mitigation challenge and much easier to agree upon than the allocation of emissions. We propose a mechanism with countries agreeing on the global carbon budget, while the decision to emit is decentralized at the country level. The revenue is collected in a global fund and allocated according to endogenously defined weights proportional to the marginal cost of climate change. The proposal features a unanimous agreement of the national citizenries of the world and global Pareto efficiency. We run a simulation in the spirit of the Paris Agreement, with zero emissions after 2055. At the Global Unanimity Equilibrium, permits are priced at 90$/tC, yielding 1.3 trillion dollars annually. Africa, India and the less developed countries in Asia are the only net recipients, while the US and China are the largest net contributors.
Mankind must cooperate to reduce GHG emissions to prevent a catastrophic rise in global temperature. How can the necessary costs of reducing GHG emissions be allocated across regions of the world, within the next few generations, and simultaneously address growth expectations and economic development? We postulate a two-region world and, based on sustainability and egalitarian criteria, calculate optimal paths in which a South, like China, and a North, like the United States, converge in welfare per capita to a path of sustained growth of 1% per year by 2080, while global CO2 emissions are restricted to the Representative Concentration Pathway RCP3-PD scenario: a conservative path that leads to the stabilization of concentrations under 450 ppm CO2, providing an expected temperature change not exceeding 2ºC.
Growth expectations in the North and the South must be scaled back substantially, not only after 2080, but also in the transition period. Global negotiations to restrict emissions to an acceptably low level cannot succeed absent such an understanding. Feasible growth paths with low levels of emissions require heavy investments in education and knowledge. Northern and Southern growth must be restricted to 1% and 2.8% per year, respectively, over the next 75 years. Politicians who wish to solve the global-warming problem must prepare their polities to accept this reality.
Suppose that there exists a positive (exogenous) probability that at each date of a possibly infinite future, the human species will disappear. We postulate an Ethical Observer (EO) who must solve an intertemporal welfare maximization problem under this kind of uncertainty, with preferences that satisfy the expected utility hypothesis. Various social welfare criteria are expressed as alternative von Neumann-Morgenstern utility functions for the EO: utilitarianism, Rawlsianism, and an extension of the latter that corrects for the size of population. Our analysis covers, first, a simple cake-eating economy, where the utilitarian and Rawlsian recommend the same intergenerational allocation. Second, we consider a productive economy with education and capital. There, however, the recommendations of the two Ethical Observers are in general (but not always) different. Surprisingly, when the utilitarian optimization program diverges, then it is optimal for the extended Rawlsian to ignore the uncertainty concerning the possible disappearance of the human species in the future. We conclude with some thoughts about what these results imply for the issue of intergenerational welfare maximization in the presence of global warming.
Climate science indicates that climate stabilization requires low GHG emissions. Is this consistent with nondecreasing human welfare?
Our welfare index, called quality of life (QuoL), emphasizes education, knowledge, and the environment. We construct and calibrate a multigenerational model with intertemporal links provided by education, physical capital, knowledge and the environment.
We reject discounted utilitarianism and adopt, first, the Intergenerational Maximin criterion, and, second, Human Development Optimization, that maximizes the QuoL of the first generation subject to a given future rate of growth. We apply these criteria to our calibrated model via a novel algorithm inspired by the turnpike property.
The computed paths yield levels of QuoL higher than the year 2000 level for all generations. They require the doubling of the fraction of labor resources devoted to the creation of knowledge relative to the reference level, whereas the fractions of labor allocated to consumption and leisure are similar to the reference ones. On the other hand, higher growth rates require substantial increases in the fraction of labor devoted to education, together with moderate increases in the fractions of labor devoted to knowledge and the investment in physical capital.