I'm not debating the idea that the glaciers are getting smaller, I spend a hell of a lot of time on and around the big three glaciers, the change is evident on much shorter timescales than a year. The issue with these glaciers (Tasman, Hooker, Mueller) is that they now terminate in proglacial lakes, and this causes the retreat to become decoupled from direct climatic factors (internal vs external forcing). Once a glacier begins to terminate in a proglacial lake they become a less robust indicator of climatic change.Manukau heads observer wrote:how about you guys opening your eyes and minds (i.e be more open minded) to other ideas as well
i.e that the glaciers are getting smaller and are retreating, in response to a warmer trend
(thats all thats is being discussed, nothing more, nothing less)(i.e it does not discuss if that warming trend is going to continue (global warming) or similar, its just stating that glaciers are a good barometer
also, comparing photos from the same angle and perspective is OK in my book (even if it might not be as good as some other method) (and no point in changing the method now, best to keep the same method going so can use past comparisons)
whats is important is the photo is take from the same spot, same angle, same time every year
which they have been
and they are showing a trend of decreasing ice accumulation (i.e melting earlier in spring and freezing later in autumn)
This is especially so in the instance of Tasman Glacier/Tasman Lake, where you now have a second, moderately large, river flowing into Tasman Lake since the mid 1990's. This has increased the temperature of the lake, and modified the currents within the lake, which is recognised to have significantly contributed to accelerating calving of the Tasman Glacier. The cause of this was a landslide on Botanical Spur. The other glaciers have experienced relatively slow proglacial lake growth.
Estimating glacier mass balance from photo's is widely recognised as being highly fickle. There are a lot of factors which cannot easily be accounted for, ie the most recent snow fall, wind direction/drifting and avalanching, to name a few, which all alter the apparent position of the EL. This is why field studies are much more robust, as the relative height of the glacier surface is measured, providing a direct measurement of the accumulation/ablation, and the accurate determination of ELA. Using photos, the ELA is determined purely based on tonal/textural differences of the snow/ice. Infrared bands of remote sensing devices can provide much more powerful analysis in this regard.
I am not disputing change in glaciers, merely trying to highlight some of the limitations of the techniques that have been used, and why we should be wary of this data. There is a fair bti of direct mass balance measurement occurring in New Zealand at the present time, which should make for some interesting publications over the next couple of years.
