Saving the planet: Emissions scenarios, stabilization issues, and uncertainties NCAR Summer Colloquium on Climate and

2. Introduction The climate change problem is essentially an energy problem that requires moving away from the use of fossil fuels as our primary energy source. This will almost certainly require the development of new �carbon-free� (or �carbon neutral�) energy technologies. To determine the magnitude of this technological challenge we need to know what will happen in the absence of policies to limit climate change, and what a safe level may be for future climate change.

3. Summary Climate changes observed over the 20th century Future climate change: the no-policy case Future climate change: stabilization policies Future changes in energy production Carbon-free energy requirements for stabilization Technology options The �wedge� concept Geoengineering

4. PAST CLIMATE CHANGE

5. Observed temperature changes

6. FUTURE CLIMATE CHANGE (in the absence of policies to reduce climate change)

7. The SRES �no-policy� emissions scenarios The Intergovernmental Panel on Climate Change (IPCC) has sponsored production of a set of 40 �no-climate-policy� emissions scenarios for GHGs, sulfur dioxide, and other gases These scenarios are based on a range of assumptions for future population and economic growth, technological change, etc., grouped into four families or �storylines� (A1, A2, B1, B2) The scenarios are published in a Special Report on Emissions Scenarios � hence the acronym SRES Six of these scenarios have been used for detailed climate calculations (A1B, A1FI, A1T, A2, B1, B2)

8. SRES scenarios: Family characteristics

9. SRES population projections

10. Economic growth: per capita GDP

11. SRES fossil CO2 emissions

12. SRES CO2 concentration projections

13. RELATIVE IMPORTANCE OF CO2

14. 2000�2100 radiative forcing breakdown

15. Global-mean temperature projections

16. Future warming compared with the past

17. THE POLICY CASE: CONCENTRATION STABILIZATION

18. Article 2 of the UNFCCC Article 2 provides the basis for climate policy. Its objective is � �stabilization of greenhouse gas concentrations �.. at a level that would prevent dangerous anthropogenic interference with the climate system �.. within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner�.

19. CO2 stabilization pathways POINTS TO NOTE Stabilization of CO2 concentration requires, eventually, very large reductions in CO2 emissions. The arrow shows the reduction in 2050 if we wish to stabilize at 450ppm Since most CO2 comes from energy usage, stabilizing CO2 requires that we need to obtain a large fraction of future energy from carbon-free sources. A key issue is, what should the stabilization level be in order to avoid �dangerous interference with the climate system�?

20. FUTURE ENERGY PRODUCTION IN THE NO-CLIMATE POLICY CASE (SRES SCENARIOS)

21. PRIMARY ENERGY BREAKDOWN NOTE: Even in the absence of climate policies, large increases are projected for carbon-free energy

22. HOW MUCH ADDITIONAL CARBON-FREE ENERGY IS REQUIRED FOR CO2 CONCENTRATION STABILIZATION? The answer depends on the assumed no-policy baseline scenario (35 possibilities in the SRES scenario set) � and on the chosen concentration stabilization level (also a wide range of possibilities). This implies a wide uncertainty range.

23. Carbon-free energy requirements

24. Extra carbon-free energy needed in 2050 (TW)

25. Extra carbon-free energy needed in 2050 (TW) POINTS TO NOTE (1) The baseline scenarios show large increases in carbon-free energy even in the absence of climate policies. This limits the options for additional carbon-free energy. (2) The large amounts of carbon-free energy required for stabilization levels of 450ppm or less will almost certainly require the development of new technologies.

26. TECHNOLOGY OPTIONS

27. CO2 emissions reduction opportunities

28. TECHNOLOGY �WEDGES�

29. Pacala & Socolow wedges

30. Baseline wedges

31. Wedges required for stabilization(through to 2055)

32. Wedges required for stabilization(through to 2055) POINTS TO NOTE Pacala and Socolow identify 15 existing technology wedges, each of which could be scaled up to reduce emissions in 2055 by 1GtC/yr However, the total number of wedges required to follow WRE450 to 2055 is between 21 and 49 We therefore need to develop new carbon-free energy technologies � probably requiring a massive investment in research, demonstration and dissemination.

33. OTHER TECHNOLOGY OPTIONS: GEOENGINEERING

34. Geoengineering (1) Reducing CO2 emissions (�mitigation� -- i.e., moving from the use of fossil fuels as our primary energy source to the use of carbon-free energy technologies) is the standard �solution� to the climate problem. Geoengineering is an alternative approach. Geoengineering aims to offset CO2-induced climate change by deliberately altering the climate system. The earliest suggestion was to inject aerosol-producing substances into the stratosphere to provide a cooling shield � i.e., to produce a human volcano.

35. Geoengineering (2) The problem with geoengineering as a single solution is that our use of fossil fuels creates two problems, climate change and increasing CO2. Increasing CO2 makes the oceans more acidic and could lead to the extinction of all carbonate shell producing animals in the ocean. As these animals are at the bottom of the food chain, their extinction could lead to the extinction of all life in the ocean. Geoengineering cannot replace mitigation (i.e., the reduction in fossil fuel use), but it may make mitigation easier.

36. Effect of multiple volcanic eruptions

37. Alternative geoengineering scenarios

38. Concentrations and implied emissions

39. Geoengineering effects on climate

40. CONCLUSIONS