Solar geoengineering and mitigation. Gernot Wagner gwagner.com

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1 Solar geoengineering and mitigation Gernot Wagner gwagner.com

2 Global carbon emissions (GtC) Le Quéré et al., Earth System Science Data (2016)

3 Wagner et al., Nature (2015)

4 450 ppm CO 2 e unachievable (circa 2009) Full participation scenario assumes maximum global $1,000/ton CO 2 tax starting 2012; delay assumes only Annex I Clark et al (2009), Stanford Energy Modeling Forum 22 No 450 ppm/2 C with mitigation alone, without massive negative emissions

5 Free rider Free driver Wagner & Weitzman, Foreign Policy (2012)

6 The Pure Theory of a Free-Driver Externality A pure public gob (good for some, bad for others) 1 2 3a Weitzman, Scandinavian Journal of Economics (2015)

7 The Pure Theory of a Free-Driver Externality A pure public gob (good for some, bad for others) 1 2 3a 3b Weitzman, Scandinavian Journal of Economics (2015)

8 The Pure Theory of a Free-Driver Externality A pure public gob (good for some, bad for others) 1 2 3a 3b 4 Nation n, which favors the most gob, decides Nash equilibrium outcome Weitzman, Scandinavian Journal of Economics (2015)

9 SRM v Mitigation (i) Hard tradeoffs (ii) Moral hazard

10 Global carbon emissions (GtC) Le Quéré et al., Earth System Science Data (2016)

11 Solar geoengineering v mitigation Solar geoengineering is not anti-co 2, but Source: Breakfast with Myles & David

12 Solar geoengineering v mitigation Solar geoengineering is not anti-co 2, but 1.5 C with 66% prob 1.5 C with 50% prob 2 C with 50% prob Source: Breakfast with Myles & David

13 Moreno-Cruz, Wagner & Keith, HKS Faculty Working Paper (July 2017)

14 SRM as CDR? RCP 8.5 vs constant 21 st century radiative forcing, an (admittedly) extreme scenario Source (primary impact) Reduction in 21 st century emissions (GtC) Reduction in 2100 burden (GtC) Carbon Cycle (burden) Permafrost (emissions) Energy sector (emissions) Total Keith, Wagner & Zabel, Nature Climate Change (forthcoming, September 2017)

15 Moral Hazard

16 Moral hazard theoretically well-founded Long history of the idea There are tradeoffs Long history in economics, introduced to solar geoengineering by Keith, History and Prospect (2000) Actually a misnomer, it s lack of self-control Some moral hazard tradeoff, really is rational some isn t Wagner & Weitzman, Climate Shock (2015)

17 What do people think when they think about solar geoengineering? A review of 30+ prior solar geoengineering surveys 1 Public unfamiliar with SRM ~20-30% have heard of geoengineering, ~2-3% can define it 45% can define climate engineering (Mercer, Keith, Sharp 2011) 2 Nuanced views of research versus deployment 3 Risk and uncertainty are important 4 Moral hazard versus Inverse Moral Hazard Most surveys show moral hazard, but Burns, Flegal, Keith, Mahajan, Tingley, Wagner, Earth s Future Crutzen+10 (2016)

18 Inverse moral hazard Germans (n=658) increase voluntary offset purchases when told about stratospheric aerosol injection (SAI) Three hypotheses: H 1 : Belief that SAI doesn t work H 2 : SAI as clarion call H 3 : SAI as threat Merk, Pönitzsch & Rehdanz, Environ. Res. Lett. (2016)

19 Inverse moral hazard? Germans (n=658) increase voluntary offset purchases when told about stratospheric aerosol injection (SAI) Three hypotheses: H 1 : Belief that SAI doesn t work H 2 : SAI as clarion call H 3 : SAI as threat Merk, Pönitzsch & Rehdanz, Environ. Res. Lett. (2016)

20 Inverse moral hazard? Germans (n=658) increase voluntary offset purchases when told about stratospheric aerosol injection (SAI) Three hypotheses: H 1 : Belief that SAI doesn t work H 2 : SAI as clarion call H 3 : SAI as threat Merk, Pönitzsch & Rehdanz, Environ. Res. Lett. (2016)

21 Inverse moral hazard? Germans (n=658) increase voluntary offset purchases when told about stratospheric aerosol injection (SAI) Three hypotheses: H 1 : Belief that SAI doesn t work H 2 : SAI as clarion call H 3 : SAI as threat Merk, Pönitzsch & Rehdanz, Environ. Res. Lett. (2016)

22 What do people really think?

23 What do people really think when they think about solar geoengineering? n=1,000, part of 36,000-subject 2016 Cooperative Congressional Election Study of US electorate, Oct-Nov 2016 Mahajan, Tingley, Wagner mimeo

24 What do people really think when they think about solar geoengineering? n=1,000, part of 36,000-subject 2016 Cooperative Congressional Election Study of US electorate, Oct-Nov 2016 Mahajan, Tingley, Wagner mimeo

25 What do people really think when they think about solar geoengineering? n=1,000, part of 36,000-subject 2016 Cooperative Congressional Election Study of US electorate, Oct-Nov 2016 Mahajan, Tingley, Wagner mimeo

26 Solar geoengineering v mitigation Not just moral hazard 1 Real tradeoffs SRM as CDR? (Keith, Wagner, Zabel, Nature Climate Change, forthcoming Sept. 2017) SRM leads to higher S, lower T, and in the context of our model higher welfare (Moreno-Cruz, Wagner & Keith, HKS Faculty Working Paper, July 2017) 2 Moral hazard v inverse moral hazard Revealed behavior (Merk, Pönitzsch & Rehdanz, Environ. Res. Lett., 2016) High-quality surveys (e.g. Mahajan, Tingley, Wagner mimeo; survey of surveys: Burns, Flegal, Keith, Mahajan, Tingley & Wagner, Earth s Future Crutzen+10, 2016)

27 Gernot Wagner gwagner.com