Updates to the IPCC WG1 Summary for Policy Makers

By Dr Flora MacTavish

The IPCC has released corrected figures for past carbon dioxide emissions and future emissions trajectories quoted in the Summary for Policy Makers of the Working Group 1 report, “Climate Change 2013: The Physical Science Basis”.  The original numbers were published in the report released on 27th September, which was subject to copy edit and final layout changes.

In total, six values from the summary have been changed. As noted by Professor Sir Brian Hoskins, Director of the Grantham Institute, these corrections are minor adjustments to historical greenhouse gas emissions and to the cumulative emissions consistent with achieving a 2 degree warming target with different levels of probability.  The 2 degree target is significant because it forms the basis of international climate change negotiations. These minor corrections do not affect any of the conclusions drawn in the Summary for Policy Makers.

Since the IPCC did not do so, I have produced the following table to compare the new values to the original values for all the parameters that have changed. For each parameter, the difference between the original best estimate and the new best estimate is given in the right hand column. This is also expressed as a percentage of the original value.  As can easily be seen, the changes in the parameters are all relatively small compared to the values of those parameters. Most are also small compared to the 90% uncertainty interval (range) given.

If you are unable to read the table below you can also view it here.

Section of the SPM affected Parameter changed Value given in the version released on 27th Sep 2013 (gigatonnes of carbon, GtC) New values, released 11th November  2013 (all in gigatonnes of carbon, GtC) Comment
Section B.5, bullet 4 Cumulative CO2 emissions from fossil fuel combustion and cement production over the period 1750 to 2011. 365 [335 to 395] 375 [345 to 405] The best estimate and range revised upwards by 10 GtC, an increase of 2.7% in the best estimate.
Section B.5, bullet 4 Cumulative anthropogenic CO2 emissions over the period 1750 to 2011. 545 [460 to 630]  555 [470 to 640] Best estimate and range revised upwards by 10 GtC, an increase of 1.8% in the best estimate.
Section B.5, bullet 5 The accumulation of carbon from anthropogenic CO2 emissions in natural terrestrial ecosystems over the period 1750 to 2011. 150 [60 to 240] 160 [70 to 250] Best estimate and range revised upwards by 10 GtC, an increase of 6.7% in the best estimate.
Section E.8, bullet 2 Total cumulative CO2 emissions from all anthropogenic sources to limit warming to less than 2°C (from CO2 alone) since the period 1861–1880 with a probability of >33%. 0 to 1560 0 to 1570 The maximum value was revised upwards by 10 GtC, a percentage increase of 0.64%.
Section E.8, bullet 2 The maximum cumulative CO2 emissions from all anthropogenic sources for limiting warming to less than 2°C (including non-CO2 forcing as in RCP2.6 – the lowest emissions scenario used by the IPCC) listed for probabilities of >33%, >50%, and >66%. 880, 840 and 800  900, 820 and 790 Numbers changed by +20, -20 and -10 GtC. The percentage changes were +2.3%, -2.4% and -1.3%.
Section E.8, bullet 2 Cumulative anthropogenic CO2 emissions over the period 1870 to 2011. 531 [446 to 616] 515 [445 to 585] Best estimate reduced by 16 GtC, a decrease of 3%. Range also reduced from 170 to 140 GtC.

 

 

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