cross-cutting themes: (1) consistent evaluation of uncertainties and (2) better treatment of economic and noneconomic costs. He summarized by emphasizing that the IPCC Fifth Assessment needs to move from emphasizing the point that climate change is real to providing information that stakeholders need.


Ottmar Edenhofer

Ottmar Edenhofer, chair of IPCC Working Group 3 (WG3), presented a WG3 perspective on the scenario process, including coordination issues. He noted that the current outline of the WG3 report frames the issue in terms of risk and then examines pathways for mitigation by sector, including a chapter on human settlements, infrastructure, and spatial planning. WG3 will look at a number of transformation pathways developed by the scientific community. It is intended that the pathways will be explicit about unintended side-effects, such as leakage from carbon storage projects and effects of bioenergy development on food security, in order to show both the mitigation choices and their implications. Edenhofer said that, although the representative concentration pathways (RCPs) provide a minimum of consistency across the working groups, there is also a need for a realistic representation of the policy space that does not simply assume that all options are feasible.

His understanding is that the RCPs will be analyzed by the climate community to yield patterns of climate change. He said that the socioeconomic variables coming from the IAM community need to be downscaled, and the assessment needs to explore the full range of transformation pathways for each RCP. He suggested that it might be useful to develop what he called RSPs—representative socioeconomic pathways—which could be a basis for connection between the IAM and the IAV communities. He said that scenarios would need to identify demographic, economic, and other drivers and could serve as exogenous drivers for baseline conditions as well as for policy scenarios. He suggested that RSPs could be combined with policy scenarios, with each combination yielding an emissions trajectory. He also suggested that the process could also develop scenarios with “second-best” policies.

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