I thought this paper was interesting, and it was (as part of a Twitter exchange) sent to me by request (thanks to Both Richard Tol and Bjørn Lomborg). I found figure 8 (shown below as part of the preview on Science Direct) to be interesting because it shows a positive impact of warming up to 2.0C and a negative impact afterwards, suggesting that some warming is beneficial, but a lot of warming is not. All things in moderation I suppose. – Anthony.
A survey of the economic impact of climate change and the marginal damage costs shows that carbon dioxide emissions are a negative externality. The estimated Pigou tax and its growth rate are too low to justify the climate policy targets set by political leaders. A lower discount rate or greater concern for the global distribution of income would justify more stringent climate policy, but would imply an overhaul of other public policy. Catastrophic risk justifies more stringent climate policy, but only to a limited extent.
Climate change is one of today’s defining problems. It is often described as the largest problem, or the largest environmental problem of the 21st century (Stern et al. 2006) – without much evidence. Climate change has been said to fundamentally challenge economics as a discipline (van den Bergh 2004). More sober people would recognize greenhouse gas emissions as an externality. It is an externality that is global, pervasive, long-term, and uncertain – but even though the scale and complexity of this externality is unprecedented, economic theory is well equipped for such problems – and advice based on rigorous economic analysis is anyway preferred to wishy-washy thinking. This paper surveys the literature on first-best climate policy.
The first benefit-cost analysis of greenhouse gas emission reduction was published in 1991 by William D. Nordhaus of Yale University (Nordhaus 1991). It was a static, aggregate analysis, but was soon followed by dynamic studies (Nordhaus 1992;Nordhaus 1993) and regionally disaggregated ones (Nordhaus and Yang 1996). Nordhaus’ research was influential and his findings controversial. Nordhaus concluded
- (i) that modest emission reduction is desirable now;
- (ii) that the ambition of climate policy should accelerate over time;
- but (iii) that the atmospheric concentration of greenhouse gases should not be stabilized.
Conclusion (ii) is qualitatively uncontroversial, but the rate of acceleration is disputed. Conclusions (i) and (iii) are controversial, within the economics profession but particularly outside.
Fig. 8. Estimates of the global economic impact of climate change (blue dots) and two fitted functions: I=4.33(1.49)T−1.92(0.56)T2 (red line) and I=0.348(0.166)T2−0.0109(0.0025)T6 (green line); the thin lines demarcate the 95% confidence interval based on the bootstrapped standard deviation.
Discussion and conclusions
I review optimal targets for international climate policy in the short and long run. Carbon dioxide emissions are probably a negative externality, and should therefore be taxed. Using a discount rate similar to the one typically used for public investments, the expected value of the carbon tax is $25/tC. That carbon tax corresponds to the initial carbon tax of a cost-effective emission reduction trajectory towards stabilization at 625 ppm CO2e – considerably higher than the implicit political aim to stabilize at 450 ppm CO2e. Furthermore, the efficient carbon tax would increase at some 2.3% per year whereas the cost-effective carbon tax would increase at some 5.5%. Efficient concentrations at the end of the 21st century would thus exceed 625 ppm CO2e.
Indeed, it is unlikely that a benefit-cost analysis would justify stabilization of the atmospheric concentration of greenhouse gases – as stipulated by international law – as that would require zero carbon dioxide emissions. Fossil fuel use may of course cease for reasons other than climate change. A lower discount rate and an aversion to inequity would justify more stringent climate policy, but would imply inconsistencies between climate policy and other areas of public policy.
Catastrophic risk is a more powerful argument for more stringent climate policy, but to a limited extent as emission reduction has downside risks too. The above analysis considers efficient climate policy in isolation. This is a useful yardstick for analysis, but not particularly realistic. Climate policy interacts with many other policies, but two
areas stand out. Climate policy is intimately intertwined with technological progress in the
energy sector and with the availability of energy resources. Recent break-throughs in the
exploitation of shale gas reduce greenhouse gas emissions in the short term (as gas replaces coal) but increase emission reduction costs in the long term (as solar now competes with cheap gas and cheap coal). Even so, optimal climate policy is unaffected provided that technology policy is first-best (Bosetti et al. 2011;Fischer 2008;Fischer and Newell 2008;Popp and Newell 2012) and that resources policy is first-best (Hoel 2012;van der Ploeg and Withagen 2012). Those are strong assumptions, yet it would not be wise to solve other problems through climate policy.
I assumed that adaptation is efficient. If so, it does not affect optimal mitigation policy (de Bruin et al. 2009). I also assumed that climate policy is implemented efficiently. In Section 3.1, I note that second- or higher-best policy implementation may be substantially more expensive. If emission abatement is more expensive, then climate policy should be less stringent.
I reasoned from the perspective of a global planner. Greenhouse gas emission reduction is, of course, a public good. A non-cooperative equilibrium has higher emissions (Babiker
2001;Barrett 1994;Carraro and Siniscalco 1992;Carraro and Siniscalco 1993;Carraro and
Siniscalco 1998;Nordhaus and Yang 1996;Yang 2003).
Although considerable progress has been in our understanding of optimal climate policy, much research remains to be done. Quantitatively, the estimates of the costs and benefits of climate policy can be improved. Incremental improvements on the current state of the art are always feasible. Both sets of estimates have primarily relied on simulation modeling, but data have steadily improved so that impacts of climate variations should be measurable (Mendelsohn et al.1994). Some countries now have two decades of experience with climate policy; the impacts and the model assumptions should be tested econometrically (Leahy and Tol 2012). Such research would add confidence to current estimates, or new insights. Qualitatively, besides carefully exploring the myriad second-best features of climate policy, research to date has been limited to a fairly narrow class of welfare functions. The assumption of exogenous population growth is
particularly troubling in the context of climate change. A convincing alternative to the intuitively incorrect conclusion that continued warming is optimum, is still elusive.