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  1. MikeH September 27, 2013 at 6:17 pm |

    On the Global surface temperature change dot point.
    “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.”

    Steve Easterbrook, professor of computer science at the University of Toronto has a comment at the Real Climate blog which puts this in perspective.

    “… the “best case scenario”, RCP2.6 is predicated on global carbon emissions peaking before 2020, and then falling fast, with the entire world becoming carbon negative by the 2070s. When the RCP scenarios were first picked, this was considered to be too unlikely to be worth looking at. The plan was to go with a higher scenario, RCP2.9, which, together with RCP4.5 bracket the lower 5% and upper 95% confidence interval for what can be achieved with strong mitigation policies. However, RCP2.9 didn’t keep temperatures under 2C of warming (over pre-industrial levels), so they decided to go with the more ambitious RCP2.6, just so there would be at least one scenario that kept below the politically important 2C threshold. Analysis is still ongoing for figuring out what it would actually take to achieve RCP2.6 (and will be release with the Working Group 3 report next year). But the key point is that it has to get us to net carbon negative (from all sources) within 60 years.”

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