date: Fri, 16 Jul 2004 08:45:49 -0600 from: Tom Wigley subject: thanks again to: Sarah Raper Sarah, Thanks again for all that useful material. I will absorb it into the text. Although it will not make much difference, I guess I should use an exponent for V in the final version of the model. I will stick to n=1 for the analytic results -- but n=1.2-1.4 seems necessary to be state of the art. As far as MAGICC goes it makes no difference since I solve the equation numerically. My 1880 start year comes from TAR p. 667 which refers to 'the climate of 1865-1895'. What is confusing is the T1990 term is relative to 'the late 19th century' (p. 682, which I take as 1865-1895, equal near enough to the 1880 value in MAGICC) --- but the g1990 is relative to the glacier steady state. There is a 0.15degC correction for the warming from this time to 1880, so the steady state time must be well before 1880. In MAGICC with DT2x=2.6degC the 1765-1880 warming is only 0.1degC. All this is accounted for in MAGICC strictly following the TAR, but there is still an inconsistency problem that I noted before (and it's worse than I said before). The AOGCM gu(1990) range is 1.5 to 2.7cm (I use the average in MAGICC). The corresponding gs(1990) value is pretty much the same. These must be changes from the glacier steady state point, which must be well before 1880 and probably before 1765. Table 11.10 (1910-1990 data) suggests a change larger than this, 2.4cm over 1910-1990 . The question is, 2.4cm from 1910 equals what from the glacier steady state point? Even though 1910 was a cool spot in the global temperature curve, the use of the 0.15 correction implies that there must be positive GSIC melt to 1880, and hence almost certainly positive melt to 1910. So the 'observed' gs(1990) must be more than 2.4cm. I guess there is nothing we can do about this. At worse we will be about 1cm too low with gs(1990) if we stick to the TAR AOGCM mean, and this won't affect the longterm behaviour which must tend to V0. What is needed is a model that runs from the steady state point rather than 1990. Probably easy to do, but it would make everything more messy and less directly comparable with the TAR. Thwarted by Jonathan's ad hockery! Tom.