Lights, camera, emissions . . . . .

It had come to Eli's attention that some folk were finding fault with the IPCC Emission Scenarios. While everyone was arguing about the alphabet soup used in the IPCC Fourth Assessment Report, in September 2007, the IPCC convened a meeting of experts to draw up new scenarios for the fifth assessment report. The approach will be quite different. First there will be near (2035) and further (2100) and way out there (2300) term scenarios.

Major motivations for the near-term scenarios are understanding the effect of emissions on air quality, providing information on trends and extreme events, and providing high-resolution output for the Impacts, Adaptation and Vulnerability community. Near-term adaptation and mitigation analyses can be matched to conventional planning time scales, can explore opportunities and constraints given institutional and technological inertia, and can play an important role in integrating climate change considerations into other areas of management and policy. Key issues on this time scale include identifying immediate risks; developing corresponding adaptive capacity; reducing vulnerability; making efficient investments to cope with climate change; and implementing investments in low emission technologies, energy conservation, and sink preservation and/or enhancement.

Models (both physical and economic and ecological) can be run at higher resolution for the near term and provide the finer grained information that policy makers need. On the other hand

The longer term policy focus shifts towards evaluating climate targets to avoid risks from climate change impacts, improving the understanding of risks of major geophysical and biogeochemical change and feedback effects, and adopting strategies for adaptation, mitigation, and development that are robust over the long term to remaining uncertainties.

Unlike the previous scenarios, the new ones will be based on four representative concentration pathways (RCPs). One will be as disaster, where the radiative forcing reaches >8.5 W/m2 by 2100 (1370 ppm CO2 equivalent) and continues increase. There will be two intermediate “stabilization pathways” with radiative forcing stabilized at 6 W/m^2 (850 ppm CO2) or 4.5 W/m^2 (650 ppm CO2) after 2100; and the Goldilocks pathway with radiative forcing peaked at 3 W/m2 (490 ppm CO2) before 2100 and declining. The scenarios will include the effects of all known forcings

The RCPs will be used to run GCMs to calculate the effects of the forcings as well as social and economic models. All of the models will be run in parallel to speed up development of the scenarios. Let the carping begin.