Side-By-Side Comparison of Draft and Final IPCC AR5 SPM on Warming Plateau and Attribution

The following table compares the IPCC’s discussions of the warming plateau and attribution from the final draft (7Jun2013) and the approved final version (27Sep2013) of the IPCC’s AR5 Summary for Policymakers.  It appears the politician agreed to delete the attribution discussion of the warming plateau.  If anyone finds something I missed the attribution discussion of the hiatus in the approved version, please let me know and I’ll correct this.

Final Draft 7Jun2013	Approved 27Sep2013
From page SPM-3:Global mean surface   temperature trends exhibit substantial decadal variability, despite the   robust multi-decadal warming since 1901 (Figure SPM 1). The rate of warming   over the past 15 years (1998−2012; 0.05 [−0.05 to +0.15] °C per decade) is   smaller than the trend since 1951 (1951−2012; 0.12 [0.08 to 0.14] °C per   decade). (Figure SPM.1) {2.4.3}	From page SPM-3:In   addition to robust multi-decadal warming, global mean surface temperature   exhibits substantial decadal and interannual variability (see Figure SPM.1).   Due to natural variability, trends based on short records are very sensitive   to the beginning and end dates and do not in general reflect long-term   climate trends. As one example, the rate of warming over the past 15 years   (1998–2012; 0.05 [–0.05 to +0.15] °C per decade), which begins with a strong   El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12   [0.08 to 0.14] °C per decade)5. {2.4}
From page SPM-9:There is very high confidence that models   reproduce the more rapid warming in the second half of the 20th century, and   the cooling immediately following large volcanic eruptions. Models do not   generally reproduce the observed reduction in surface warming trend over the   last 10–15 years. There is medium confidence   that this difference between models and observations is to a   substantial degree caused by unpredictable climate variability, with possible   contributions from inadequacies in the solar, volcanic, and aerosol forcings   used by the models and, in some models, from too strong a response to   increasing greenhouse-gas forcing. {9.4.1, 10.3.1, 11.3.2; Box 9.2}	From page SPM-10:The   observed reduction in surface warming trend over the period 1998–2012 as   compared to the period 1951–2012, is due in roughly equal measaure to a reduced   trend in radiative forcing and a cooling contribution from internal   variability, which includes a possible redistribution of heat within the   ocean (medium confidence).   The reduced trend in radiative forcing is primarily due to volcanic eruptions   and the timing of the downward phase of the 11-year solar cycle. However,   there is low confidence in   quantifying the role of changes in radiative forcing in causing the reduced   warming trend. There is medium   confidence that internal decadal variability causes to a substantial   degree the difference between observations and the simulations; the latter   are not expected to reproduce the timing of internal variability. There may   also be a contribution from forcing inadequacies and, in some models, an   overestimate of the response to increasing greenhouse gas and other anthropogenic   forcing (dominated by the effects of aerosols). {9.4, Box 9.2, 10.3, Box   10.2, 11.3}
On Attribution, page SPM-11The observed   warming since 1951 can be attributed to the different natural and   anthropogenic drivers and their contributions can now be quantified.   Greenhouse gases contributed a global mean surface warming likely to be in the range of 0.5°C   to 1.3 °C over the period 1951−2010, with the contributions from other   anthropogenic forcings, including the cooling effect of aerosols, likely to be in the range of −0.6°C   to 0.1 °C. The contributions from natural forcings are likely to be in the range of −0.1°C   to 0.1 °C, and from internal variability likely to be in the range of −0.1°C to 0.1°C. Together these   assessed contributions are consistent with the observed warming of approximately   0.6°C over this period.{10.3.1}	On Attribution, page SPM-12 & 13Greenhouse gases contributed a global mean surface   warming likely to be in the range of   0.5°C to 1.3°C over the period 1951−2010, with the contributions from other   anthropogenic forcings, including the cooling effect of aerosols, likely to   be in the range of −0.6°C to 0.1°C. The contribution from natural forcings is   likely to be in the range of −0.1°C to 0.1°C, and from internal   variability is likely to be in the range of −0.1°C to 0.1°C. Together   these assessed contributions are consistent with the observed warming of   approximately 0.6°C to 0.7°C over this period. {10.3}
On Hiatus Attribution, page SPM-11The observed   reduction in warming trend over the period 1998–2012 as compared to the   period 1951-2012, is due in roughly equal measure to a cooling contribution   from internal variability and a reduced trend in radiative forcing (medium confidence). The reduced   trend in radiative forcing is primarily due to volcanic eruptions and the   downward phase of the current solar cycle. However, there is low confidence in quantifying the   role of changes in radiative forcing in causing this reduced warming trend.   {Box 9.2; 10.3.1; Box 10.2}	On Hiatus Attribution… (Nothing)Update: (Thanks, Lance Wallace)  In part, this discussion was moved to the earlier discussion on page SPM-10.  However, they did not include the discussion of “confidences” about the causes that were found in the draft.

SHAMELESS PLUG

If this subject interests you, then you need to check out my new book Climate Models Fail.