A risk-based framework for assessing the effectiveness of geoengineering

Transcription

1 A risk-based framework for assessing the effectiveness of geoengineering Angus Ferraro Andrew Charlton-Perez, Ellie Highwood (University of Reading)

2 Engineering the climate Decrease absorbed solar radiation by Mirrors in space Marine cloud brightening Stratospheric aerosol injection 2

3 Engineering the climate Decrease absorbed solar radiation by Mirrors in space Marine cloud brightening Stratospheric aerosol injection Only sensible if we believe a geoengineered climate could be better than a plausible non-geoengineered climate How do we find out? 3

4 Solar geoengineering is cheap Stratospheric aerosol injection costs about $10 bn per year 'Essentially costless' according to David Keith McClellan et al (2012) doi: / /7/3/

5 Solar geoengineering is cheap but is it effective? 5

6 Geoengineering reduces climate damages Climate damage depends on: Magnitude of T, P change relative to variability Sensitivity of region to these changes 6

7 Regional inequalities spur international conflict Mitigation Low coalition participitation - free-riding Large coalition is preferable to maximise benefits everyone has to do mitigation to make it cost-effective Katharine L Ricke et al 2013 Environ. Res. Lett , Strategic incentives for climate geoengineering coalitions to exclude broad participation, doi: / /8/1/

8 Regional inequalities spur international conflict Mitigation Low coalition participitation - free-riding Large coalition is preferable to maximise benefits everyone has to do mitigation to make it cost-effective Geoengineering Low coalition participitation but high incentive to participate (since geoengineering is 'costless') Small coalition preferable to maximise benefits regional differences in preferred level of geoengineering Katharine L Ricke et al 2013 Environ. Res. Lett , Strategic incentives for climate geoengineering coalitions to exclude broad participation, doi: / /8/1/

9 Regional inequalities spur international conflict 9

10 What is climate risk? Probability of experiencing undesirable climate events, weighted by vulnerability ' 10

11 What is climate risk? Probability of experiencing undesirable climate events, weighted by vulnerability Assume climate events are driven by temperature and precipitation 11

12 What is climate risk? Probability of experiencing undesirable climate events, weighted by vulnerability Assume climate events are driven by temperature and precipitation What is 'undesirable'? Naively: 'change is bad' 12

13 Risk ratio p geoeng RR= PCO2 Geoengineering is a treatment for the symptoms of a 'disease' (elevated atmospheric CO2) Success of treatment depends on the extent to which it reduces the risk of experiencing the symptoms 13

14 Application to model simulations Reading Intermediate General Circulation Model (IGCM) with 100m slab ocean T42L35 resolution (~2.5 degrees) 80-year simulations 65 years analysed Name CO2 concentration (ppmv) Geoengineering Global-mean T anomaly (K) Control CO CO2+Sulphate 1148 Sulphate aerosol CO2+Solar % solar dimming

15 Classification of regional risks p geoeng RR= PCO2 What is the probability of a region experiencing a temperature or precipitation anomaly exceeding a given threshold? 15

16 Classification of regional risks Temperature Precipitation 16

17 Regional disparities in effectiveness 17

18 Summary metrics 18

19 Sensitivities 19

20 Potential problems Sensitivity to the definition of 'substantial change' Need to select threshold carefully 20

21 Potential problems Sensitivity to the definition of 'substantial change' Need to select threshold carefully Assumed 'damage' caused by increases and decreases in temperature and precipitation is the same 21

22 Flexibility of method Easy to modify for different 'symptoms' Assuming threshold carefully selected 22

23 Flexibility of method Easy to modify for different 'symptoms' Assuming threshold carefully selected Select different time resolution Most 'climate events' are sub-annual 23

24 Flexibility of method Easy to modify for different 'symptoms' Select different time resolution Assuming threshold carefully selected Most 'climate events' are sub-annual Vulnerability weighting / loss function Regional Symptomatic 24

25 Flexibility of method Easy to modify for different 'symptoms' Select different time resolution Assuming threshold carefully selected Most 'climate events' are sub-annual Vulnerability weighting / loss function Regional Symptomatic Some symptoms are not treated at all (ocean acidification) 25

26 Transient risk assessment 26

27 Potential problems It's a basically a way of presenting climate model output do we believe models? 27

28 Potential problems It's a basically a way of presenting climate model output do we believe models? It's too complicated To make it relevant to the real world lots of parameters need to be correctly set 28

29 Potential problems It's a basically a way of presenting climate model output do we believe models? It's too complicated To make it relevant to the real world lots of parameters need to be correctly set It's too simple It's a simple transformation of simple climate variables with limited applicability to real-world vulnerabilities to climate events 29

30 Summary Optimisation requires trade-off Broader public input is crucial This risk framework offers a way of intuitively summarising climate model output For comparison between models For optimising the level / type of geoengineering Ferraro AJ, Charlton-Perez AJ, Highwood EJ (2014) A Risk-Based Framework for Assessing the Effectiveness of Stratospheric Aerosol Geoengineering. PLoS ONE 9(2): e doi: /journal.pone