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First thoughts on IPCC SPM — Did I find an error?

February 2nd, 2007 by Sean Davis · 7 Comments

So I wanted to post some initial thoughts on the IPCC Summary for Policy Makers that just came out, but noticed that there are already some interesting posts at RealClimate and Prometheus on the topic.

RealClimate has an interesting brief summary of some of the new and interesting points in the SPM, and, perhaps shocking to some, Roger Pielke, Jr. at Prometheus is pleasantly surprised with the treatment of the tropical cyclone-GHG issue in the SPM.

I haven’t finished reading this document completely, so I hope for a more complete post on the subject later. But one thing that immediately struck me was an apparent error I noticed in Table SPM-0 (and trust me, I wasn’t just going through this looking for errors!)

spm0.PNG
If you sum up the contributions to sea level rise from 1993-2003 in table SPM-O, you get 0.657, not 0.28. I think they messed up the Greenland and Antarctic values, which they list as 0.21 (each). If you assume they are 0.021 instead, the sum total contribution does add up to 0.28, which is what they have listed there.

Am I missing something here? Anyone?

Also, for the 1961-2003 column, the Antarctic ice sheet contribution to sea level rise is GREATER than the sum of individual contributions to sea level rise.

OOPS!

Perhaps I’m just being dense here and missing something really obvious. Or perhaps in their rush to get this thing out the door, they just shifted some decimal point. …Like in that movie Office Space.

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7 responses so far ↓

  • 1 seand // Feb 2, 2007 at 2:03 pm

    According to Stefan at RealClimate, he also noticed this and alerted the IPCC. So I’m not going crazy…

  • 2 seand // Feb 2, 2007 at 3:42 pm

    More detail on the 1961-2003 column. If you assume they meant 0.014 instead of 0.14 for the Antarctic contribution, the numbers in the 1961-2003 column STILL don’t add up (i.e. .042+.05+.05+.014 = .156, NOT .11 as they have in the table)

  • 3 James Hammond // Feb 2, 2007 at 7:25 pm

    There is a note at the top of the page that “Numbers are to be converted to mm per year” from meters per century. This would increase the numbers by a factor of 10.

    If only the Greenland and Antarctic numbers in both columns are in mm/year and we divide those by 10, the columns add up nicely.

  • 4 Lubos Motl // Feb 2, 2007 at 9:14 pm

    Dear Sean, congratulations to your finding. Stefan confirmed that it seems as a clear bug, and I confirm it, too. See also

    http://motls.blogspot.com/2007/02/summary-for-policymakers.html

    Concerning the origin of the error, I think that the errors will be in signs. For example, the contribution of Antarctica is negative, see IPCC 2001:

    http://www.grida.no/climate/ipcc_tar/wg1/409.htm

    It’s between minus 0.17 and plus 0.02 meters per century.

    I just wander that minus 20 centimeters from Antarctica wouldn’t sound sufficiently attractive for the policymakers. ;-)

    Still, I don’t know how to add the numbers to get the right (?) results, especially not the error bars. The sum seems to be 5-10 more accurate than the Antarctic contribution in both cases.

  • 5 Mike Mills // Feb 7, 2007 at 5:21 pm

    Sean,

    This error has been corrected in the final draft of the SPM, available today online at http://www.ipcc.ch/SPM2feb07.pdf

    It was the totals that should be multiplied by 10:
    Sum of individual climate
    contributions to sea level rise 1.1 ± 0.5 2.8 ± 0.7
    Observed total sea level rise 1.8 ± 0.5 3.1 ± 0.7

  • 6 Mike Mills // Feb 7, 2007 at 5:25 pm

    Er, that is everything except Greenland and Antarctica got multiplied by 10 in the corrected draft, and units changed to mm per year.

  • 7 Don Thieme // Feb 8, 2007 at 7:21 pm

    I posted the three report tables, with the recently corrected version of Table SPM-0, here:

    http://www.gpc.edu/~dthieme/Weather/IPCC_AR4.htm

    The confusion was in going from meters per century to mm per year.

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