Climate Change impacts for emission paths that peak and decline Authors: Chris Hope,

1. Climate Change impacts for emission paths that peak and decline Authors: Chris Hope, Judge Business School, University of Cambridge Rachel Warren, Tyndall Centre, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ Jason Lowe, MetOffice Hadley Centre (Reading Unit), Department of Meteorology, University of Reading, Reading, RG6 6BB and the AVOID WS1 Team AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs

2. The Scenarios Emission scenarios: varied year in which emissions peak globally, the rate of emission reduction (R), and the minimum level to which emissions are eventually reduced (H or L). Focused on 2015-2044 (centred on 2030) 2035-2064 (centred on 2050) 2070-2099 (centred on 2085) Scenarios: A1B, and policy scenarios 2030.R2.H, 2030.R5.L, 2016.R2.H, 2016.R4.L and 2016.R.Low

4. Temperature implications: Jason Lowe’s analysis showed that …

5. Temperature implications Jason Lowe’s work told us: Under A1B temperatures are likely to reach 3-4C 2030 peaking insufficient for 2C and have chance of 1 in 3 to 4 of exceeding 3C 2016 targets effective at avoiding 3C, chance of exceeding falls to 1 in 10 Only most stringent R=5% 2016 scenario has 45% chance to meet 2C target All avoid temperatures reaching 4 degrees with high confidence (>=98%) except for 2030 2% L which leaves a 7% chance of more than 4C.

6. The earlier the peak in emissions, the greater the avoided impacts AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs

7. The earlier the peak in emissions, the greater the avoided impacts

8. Global coastal flood plain population in the 2020s, 2050s and 2080s under the different sea-level rise scenarios

9. Net global losses of saltmarsh by the 2080s due to sea-level rise, including uncertainty

10. Key message: Date at whichemissions peak critical Example: water stress: by the 2080s, the 2016R scenarios remove 38-41% of the increases in water stress forcecast under A1B (HadCM3 50% outcome) whereas the 2030R scenarios remove only 33%. Example, coastal zone: avoided impacts in terms of people experiencing coastal flooding are large, about 43% by the 2080s in the 2016.R scenarios, where in the 2030.R scenarios it is 30%. Example, biodiversity: 55-77% of climate change induced extinction risks in European plants avoided in 2016R scenarios compared to 44% under 2030.R

11. Date at which emissions peak critical Avoided impacts resulting from reducing emissions from A1B scenario to 2016R scenarios are greater than for the 2030R scenarios …in all three of the sectors: water stress, coasts, biodiversity Hence date at which emissions peak is more important than the rate of subsequent emissions reduction in determining the avoided impacts

12. Scope of the PAGE2002 model • The major greenhouse gases. • Economic, non-economic and cat- • astrophic impacts. • Time horizon of 2200. • Probabilistic calculations • Eight world regions

13. Inputs to PAGE model Emissions of greenhouse gases Atmospheric residence time of greenhouse gases Sensitivity of the climate system Cooling effect of sulphates Impacts as a function of temperature change

14. Inputs to the PAGE2002 model Discount rates and equity weights: The Stern runs used a ptp rate of 0.1% per year and an EMUC of 1. Gives a mean discount rate of about 1.5% per year, varying over time and across regions. The AVOID runs used triangular distributions for both. ptp rate of <0.1,1,2> % per year. EMUC of <0.5,1,2>. Gives a mean discount rate of about 3% per year

15. Structure of the PAGE2002 model

16. The earlier the peak in emissions, the greater the avoided impacts

18. Economic evidence: Date at whichemissions peak critical PAGE also confirms that the date at which global emissions peak is a stronger driver of avoided impacts than is the rate at which emissions are subsequently reduced A1B: equity weighted climate change impacts reach ~$32 trillion year 2000 US$ (range 29-83 trillion $$) or ~4% of global GDP by 2100 (1-12%) By 2100 policy scenarios in which emissions peak in 2016 avoid ~ 20 trillion (19-19.7 across scenarios) US2000$. (The 5-95% range is 4.6-54 trillion) compared to A1B. i.e. 2.6-2.7% of 2100 GDP (range 0.6-7.4%GDP). Thus two thirds of impacts may be avoided. By 2100 policy scenarios in which emissions peak in 2030 avoid ~15 trillion (14-16) US2000$ (3.5--45 trillion) compared to the A1B i.e. 2.0-2.2% of year 2100 GDP (range 0.5-6.1). Thus half of the impacts may be avoided.

19. CONCLUSION Date at which emissions peak is more important than the rate of subsequent emissions reduction in determining the avoided impacts Demonstrated with INDEPENDENT economic and physically based impacts analyses AVOID is funded by the Department of Energy and Climate Change and the Department for Environment, Food and Rural Affairs