Thanks for contributing this, TG. My thoughts:
1. The IPCC was indeed very wrong on this one, the original work having been done in the Kotlyakov report (1996) which gave the date of 2350 for the disappearance of most of the Himalayan glaciers.
2. These kinds of non-apocalyptic timescales are backed by another, more recent report, An assessment of the potential impacts of climatic warming on glacier-fed river flow in the Himalaya (2006) by Rees & Collins.
A regional hydro-glaciological model has been developed to assess the potential impacts of climatic warming on glacier-fed river flows in the Indus and Ganges basins. The model, applied at a 20 km x 20 km grid resolution, considers glaciers contributing runoff to a cell as a single idealized glacier that is allowed to recede through time. Using 1961-1990 climate data as input, baseline flow estimates were derived for every stretch of river in either basin. A transient warming scenario of +0.06°C years-1 was then imposed for 100 years from an arbitrary start-date of 1991. Comparison of results at 10 sites in two representative areas suggest the impacts of such climatic warming are similar regionally, with estimates of future decadal mean flows continually increasing at 1-4% per decade, relative to baseline, at most sites considered. Flows peaked at only two of the sites several decades into the model run.
3. The worst affected region by far in the event of glacier meltdown would be the Indus (and Pakistan), which is almost entirely reliant on glacier runoff; the other great Asian rivers derive a great deal of their flow from the monsoon, so presumably agricultural civilization will be able to survive in the non-Pakistani parts of the Indian subcontinent as long as a) the monsoons continue, b) irrigation is practiced, c) new rice varieties are developed that are able to cope with increased heat stress, and d) said areas don't fall into so-called "zones of uninhabitability,
4. That said, I should still stress that there are far more unknowns than knowns in all this. Some possibilities that might make the dire predictions of meltdown by around 2050 more plausible:
a) Not a lot of research done, AFAIK, on the brown soot and particulates deposited by Indian cook-fires and industrializing China on the Himalayas, which when embedded in the ice massively accelerate melting since they are "black bodies" (even though ironically they shield the Himalayas from some of the heat).
b) Referring to the report in 2): I'm not sure representing melting glaciers contributing runoff to a cell as a "single idealized glacier" is very rigorous. There could be runaway mechanisms similar to the ones recently discovered for Greenland and Antarctic (i.e. moulins).
5. Though the 2035 date seems to have been invalidated, more research needs to be done before we can ascertain that the situation really is as non-threatening as implied by Kotlyakov and Rees & Collins work.
EDIT: 6. I had a look at the Kotlyakov report (1) in more detail:
Taking air temperature records of the Tien Shari Weather Station and assuming that the same linear trend is to keep up (unfortunately, linear extrapolation is inevitable here), we may find that the mean annual temperature in Central Asia may go up 1.5° C by the year 2350. Proceeding from these rough estimates, in Tables 10, and 11 we have derived figures for glaciation shrinkage DS, changes in the specific glacier melt runoff Rd and the volume of this runoff QRd, as well as for the overall rise of the ocean level Z SL. These data apply to Central Asian glaciers and all of the extrapolar glaciation of the Earth.
...
... The extrapolar glaciation of the Earth will be decaying at rapid, catastrophic rates—its total area will shrink from 500,000 to 100,000 km² by the year 2350.
Hmmm... so he is modeling a (linear!) 1.5C temperature rise over Central Asia during the century, when the projected global average for just the next century ranges up to as high as 6.1C (IPCC) and increases exponentially over time (and that's discounting tipping points, the dimming effect, the "Archer bonus", etc).
