Looking to the Future

The IPCC Summary from Policymakers (after all they got to approve every sentence of the thing) is occupying the blogs, with continued focus on climate sensitivity, ocean heat content, sea level rise and more. 

To Eli, an important bottom line can be found in the boxed statement on the last page

Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO2 are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO2.

which is expanded on below,

A large fraction of anthropogenic climate change resulting from CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Depending on the scenario, about 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1,000 years.

Bunnies have to keep in mind that the most optimistic of the scenarios, RCP 2.6, the one where the world gets serious about climate change, requires huge reductions in the carbon dioxide emissions,

By 2050, annual CO2 emissions derived from Earth System Models following RCP2.6 are smaller than 1990 emissions (by 14% to 96%). By the end of the 21st century, about half of the models infer emissions slightly above zero, while the other half infer a net removal of CO2 from the atmosphere.

The Sueddeutscher Zeitung reports that this originally said that by 2050 emissions had to be halved to avoid the 2 C boundary, but that the Saudi's insisted this be changed to (by 14% to 96%).  The scientific consensus limited the damage because in a meeting of nations credibility is important and the full Inhofe only produces sniggling.

In looking at the projections of global temperatures, one has to keep in mind that there are different projections for different scenarios

Global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850 to 1900 for all RCP scenarios except RCP2.6. It is likely to exceed 2°C for RCP6.0 and RCP8.5, and more likely than not to exceed 2°C for RCP4.5. Warming will continue beyond 2100 under all RCP scenarios except RCP2.6. Warming will continue to exhibit interannual-to-decadal variability and will not be regionally uniform

and pay careful attention to that word exceed

Increase of global mean surface temperatures for 2081–2100 relative to 1986–2005 is projected to likely be in the ranges derived from the concentration driven CMIP5 model simulations, that is, 0.3°C to 1.7°C (RCP2.6), 1.1°C to 2.6°C (RCP4.5), 1.4°C to 3.1°C (RCP6.0), 2.6°C to 4.8°C (RCP8.5). The Arctic region will warm more rapidly than the global mean, and mean warming over land will be larger than over the ocean (very high confidence).

Somebunnies will attempt to use the wide range of projections, 0.3 to 4.8 to cast doubt.  Point out that the range for no action 2.6°C to 4.8°C, is much more precise, very scary, and in no way a walk in the park for their kid's kid's.

Summaries at Real Climate,