My trip to New Zealand included a great look at the world heritage Fox and Franz Joseph Glaciers. It was interesting to see how they moved. In general, these glaciers increase in size by about 1.5 meters a day which is huge compared to other parts in the world. This is caused by snowfall and the n?v?, which is at the very top of the glacier or top of the mountain. But the glacier also melts at the terminus, which is the very bottom of the glacier. Depending on how quickly the snow falls up the top and the temperature down the bottom defines if the glacier increased in length or not. Obviously the two factors are highly correlated. There is a 5 year delay in the amount of snow falling at the n?v? and the length of the glacier. E.g. If we had a bumper snow fall this year, it would take 5 years to see the effect of this on the length of the glacier.
Now for a bit of history. Back in the ice age, around 10,000 years ago the glacier actually fed into the Tasman Sea. But since then has been case of gradual decrease. In fact sign posts around show where the glacier was in 1740 and 1840 and today based on rock studies and more recently photographs and explorers diary?s. But since the mid 1980?s the glacier has actually grown in size. In the mid 1970s the glacier was nothing great to look at, and could hardly be seen from the lookout post, but it has grown quite a bit since, in some cases growing by as much as 70cm in a day.
So what does this mean? Well obviously the length of the glacier has a strong relationship with temperature in the region. This means that the glacier was at it?s longest when the ice age was, and hence we were at our coldest (obviously). Since then, we?ve been coming out of an ice age until about the mid 1970?s, where the weather must have got a lot colder.
So this area of New Zealand has therefore been warming up considerably from about 1750 to 1970 and then getting a bit colder since. This goes against the world wide temperature data of an increase in temperature from 1970, and it also shows that the increase in temperature from 1750 to 1970s was not due to CO2.
Of course I don?t have data on NZ temperatures, so my case suggesting temperature increases and decreases in this area is largely an assumption. There might well be other means of why the glaciers increase and decrease in size that has yet to be discovered (human physical contact perhaps?). However, temperature is largely correlated to the size of the glacier, and this suggests to me that we were still coming out the influences of the last ice age, and that two things just aren?t heating up as much as we expect, if at all, in the central-western region of the South Island of New Zealand.
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