2.6: Limiting climate change to 450Â ppm CO2 equivalent in the 21st century

The EMF 22 subgroup on Transition Scenarios explores a rich suite of potential future worlds in which climate change is limited to a variety of alternative radiative forcing levels. This paper focuses primarily on the requirements to limit radiative forcing from Kyoto gases to 2.6 W/m2. Given that we estimate year 2005 radiative forcing to be 2.4 W/m2, the 2.6 W/m2 limit creates a non-trivial constraint. Allowing radiative forcing to exceed the long-term target level provides greater latitude in achieving the goal, but implies major changes to both global energy and land-use systems in the near term as well as the long term. In addition, delay on the part of major emitting parties creates potential “leakage” in both energy and land use. We estimate the challenging near-term and long-term deployment of new wind power, nuclear power and CO2 capture and storage associated with the 2.6 W/m2 limit.