Debating climate economics: a response to Ackerman's critique of climate damage modeling

Ackerman and Munitz (2016) offer a critique of estimates of the economic impact of climate change and the social cost of carbon in general, and the FUND model in particular. I am grateful for the opportunity to reply. In this response, I note that (i) their concerns are not new; (ii) they highlight strengths of FUND rather than its weaknesses; and (iii) they revisit their old mistakes. I conclude with a few improvements to FUND prompted by Messrs Ackerman and Munitz

ON INTERNATIONAL EQUITY WEIGHTS AND NATIONAL DECISION MAKING ON CLIMATE CHANGE

Estimates of the marginal damage costs of carbon dioxide emissions require the aggregation of monetised impacts of climate change over people with different incomes and in different jurisdictions. Implicitly or explicitly, such estimates assume a social welfare function and hence a particular attitude towards equity and justice. We show that previous approaches to equity weighing are inappropriate from a national decision maker’s point of view, because domestic impacts are not valued at domestic values. We propose four alternatives (sovereignty, altruism, good neighbour, and compensation) with different views on concern for and liability towards foreigners. The four alternatives imply radically estimates of the social cost of carbon and hence the optimal intensity of climate policy.Domestic climate policy, social cost of carbon, equity weights

ON INTERNATIONAL EQUITY WEIGHTS AND NATIONAL DECISION MAKING ON CLIMATE CHANGE. ESRI Research Bulletin 2010/4/2

Climate change is a moral problem. The main reason to reduce greenhouse gas emissions is a concern for faraway lands (Schelling 2000), distant futures (Nordhaus 1982), and remote probabilities (Weitzman 2009). The people who emit most are least affected by climate change, and the benefits of their abatement would be diffused. Carbon dioxide dwells in the atmosphere for decades and the effects on temperature and sea level play out over even longer periods. On central projections climate change and its impacts are a nuisance for rich countries and a problem for poor countries. But there is a chance that things will go horribly wrong. If you do not care about risk, the future, or other people, then you have little reason to care about climate change

Government Failure and Market Failure: On the Inefficiency of Environmental and Energy Policy

In this essay, we describe some important themes in energy and environmental policy. There are two main reasons for our interest in these policies. First, such policies will likely be important in the coming decades as issues related to climate change and energy security come to the fore. Second, there are important lessons to be learned from a careful review of the actual performance of energy and environmental policies. We undertake a selective survey of the literature to highlight what is known about the efficiency of particular kinds of policies, laws and regulations in these areas.

On International Equity Weights and National Decision Making on Climate Change

Estimates of the marginal damage costs of carbon dioxide emissions require the aggregation of monetised impacts of climate change over people with different incomes and in different jurisdictions. Implicitly or explicitly, such estimates assume a social welfare function and hence a particular attitude towards equity and justice. We show that previous approaches to equity weighing are inappropriate from a national decision maker’s point of view, because domestic impacts are not valued at domestic values. We propose four alternatives (sovereignty, altruism, good neighbour, and compensation) with different views on concern for and liability towards foreigners. The four alternatives imply radically estimates of the social cost of carbon and hence the optimal intensity of climate policy.Domestic Climate Policy, Social Cost of Carbon, Equity Weights

Energy Use and Appliance Ownership in Ireland. WP278. February 2009

A necessary condition of an efficient global climate change mitigation policy is to equate marginal abatement costs across world regions to ensure use of the cheapest abatement options available. The welfare economic justification for such an approach rests on lump sum transfers between regions to compensate for any unwanted distributional consequences of such a policy. I contrast this efficient solution with a second best situation in which lump sum transfers between regions are impossible. I derive that in a dynamic setting optimal taxes are different in such a case for regions with different per capita consumption. I estimate the optimal tax rates with the integrated assessment model FUND and find that optimal mitigation is less stringent when equity is explicitly considered for widely used parameter choices of a utilitarian social welfare function

On International Equity Weights and National Decision Making on Climate Change

Estimates of the marginal damage costs of carbon dioxide emissions require the aggregation of monetised impacts of climate change over people with different incomes and in different jurisdictions. Implicitly or explicitly, such estimates assume a social welfare function and hence a particular attitude towards equity and justice. We show that previous approaches to equity weighing are inappropriate from a national decision maker’s point of view, because domestic impacts are not valued at domestic values. We propose four alternatives (sovereignty, altruism, good neighbour, and compensation) with different views on concern for and liability towards foreigners. The four alternatives imply radically estimates of the social cost of carbon and hence the optimal intensity of climate policy.domestic climate policy, social cost of carbon, equity weights

Equity weighting and the marginal damage costs of climate change

Climate change would impact different countries differently, and different countries have different levels of development. Equity-weighted estimates of the (marginal) impact of greenhouse gas emissions reflect these differences. Equity-weighted estimates of the marginal damage cost of carbon dioxide emissions are substantially higher than estimates without equity-weights; equity-weights may also change the sign of the social cost estimates. Equity weights need to be normalised. Our estimates differ by two orders of magnitude depending on the region of normalisation. A discounting error of equity weighted social cost of carbon estimates in earlier work (Tol, Energy Journal, 1999), led to an error of a factor two. Equity-weighted estimates are sensitive to the resolution of the impact estimates. Depending on the assumed intra-regional income distribution, estimates may be more than twice as high if national rather than regional impacts are aggregated. The assumed scenario is important too, not only because different scenarios have different emissions and hence warming, but also because different scenarios have different income differences, different growth rates, and different vulnerabilities. Because of this, variations in the assumed inequity aversion have little effect on the marginal damage cost in some scenarios, and a large effect in other scenarios.marginal damage costs, climate change, equity

Equity Weighting and the Marginal Damage Costs of Climate Change

Climate change would impact different countries differently, and different countries have different levels of development. Equity-weighted estimates of the (marginal) impact of greenhouse gas emissions reflect these differences. Equity-weighted estimates of the marginal damage cost of carbon dioxide emissions are substantially higher than estimates without equity-weights; equity-weights may also change the sign of the social cost estimates. Equity weights need to be normalised. Our estimates differ by two orders of magnitude depending on the region of normalisation. A discounting error of equity weighted social cost of carbon estimates in earlier work (Tol, Energy Journal, 1999), led to an error of a factor two. Equity-weighted estimates are sensitive to the resolution of the impact estimates. Depending on the assumed intra-regional income distribution, estimates may be more than twice as high if national rather than regional impacts are aggregated. The assumed scenario is important too, not only because different scenarios have different emissions and hence warming, but also because different scenarios have different income differences, different growth rates, and different vulnerabilities. Because of this, variations in the assumed inequity aversion have little effect on the marginal damage cost in some scenarios, and a large effect in other scenarios.Marginal Damage Costs, Climate Change, Equity