1. Assessment of contributions to climate change Results of phase II Bracknell 25 September 2002 Niklas Höhne ECOFYS energy & environment

2. Questions: What is the effect of taking non- linearities into account? Which indicators should be used to describe contributions to climate change?

3. Simplified cause-effect chain from emissions to climate change Emissions N 2 O Concentrations N 2 O Emissions CH 4 Concentrations CH 4 Emissions CO 2 Concentrations CO 2 Radiative forcing Temperature change Damages...

4. Effect of peak emissions Radiative forcing Global CO 2 emissions Concentrations Temperature increase

5. Effect of peak emissions Radiative forcing Global CO 2 emissions Concentrations Temperature increase

6. Conclusions Non-linearities Including non-linearities Realistic representation of the climate system Counting ‘late’ emissions substantially less Not including non-linearities Unrealistic representation of the climate system Counting all emissions independent of emissions of others - ‘all emissions are equal’

7. Simplified cause-effect chain from emissions to climate change Emissions N 2 O Concentrations N 2 O Emissions CH 4 Concentrations CH 4 Emissions CO 2 Concentrations CO 2 Radiative forcing Temperature change Damages...

8. Characteristics of indicators Certain and simple-> Near top of cause-effect chain Close to impacts -> Near bottom of cause-effect chain ‘Backward looking’: Taking into account the path of historical emissions ‘Backward discounting’: Weighing less what was emitted longer ago ‘Forward looking’: Accounting for the effects that occur in the years after emission Comparable for all greenhouse gases

9. Indicators for historical responsibility Time Radiative forcing Time Emissions Time A B C E F Concentrations

10. Comparison Backward Backward Forward lookingdiscountinglooking Current radiative forcing--- Current GWP-weighted --X emissions Radiative forcing from XX- increased concentrations Cumulative GWP-weighted X-X emissions Weighted concentrationsXXX Temperature increaseXX- also discounting most recent emissions

11. Conclusions Indicators Several for historical responsibility for climate change are available Of those considered only one (weighted concentrations) is ‘backward looking’, ‘backward discounting’ and ‘forward looking’ Use a simple indicators ????

12. Current radiative forcing of current emissions Fossil and industrial CO2 All gases

13. GWP-weighted emissions Fossil and industrial CO2 All gases

14. Radiative forcing due to increased concentrations Fossil and industrial CO2 All gases

15. Cumulative GWP-weighted emissions Fossil and industrial CO2 All gases

16. Weighted concentrations Fossil and industrial CO2 All gases

17. Temperature increase Brazilian Proposal Fossil and industrial CO2 All gases