Retorts

Dickensian Winters

There has never been any doubt that the Little Ice Age and the Dickensian Winters [Quick Dips, March 1996] were global phenomena -- it's hard to comprehend the need for proof that their effects were felt in New Zealand, but I guess it was interesting and well-paid work for the scientists involved.

Man was aware of the variation on the Sun's surface, as evidenced by sunspots, before he started measuring temperatures. Sunspots vary, first on a short cycle averaging about 11 years, and, less consistently, over greater periods of time. Research this decade has established that solar radiation varies in step with sunspot activity, and that this has been the major cause of Nature's variation in global temperature during the last millennium.

In the Dickensian Winters, they knew that the sunspot activity was low, whether or not the low temperatures were attributed to this. Before this, in the even-colder Little Ice Age (1650-1710), a phenomenal complete absence of sunspots was recorded.

The high temperature of the Little Climatic Optimum, more than 1.5^o above our current "fearful high", is related to these sunspots associated with magnetic activity on the Sun. In those earlier days (1000-1200 AD) Man probably knew nothing about sunspots. But today's scientists have established that the sunspot activity of that period was high.

Cosmic rays emitted by the Sun cause the steady production in the atmosphere of the carbon isotope, C14, which in turn reverts, with a half life of 5,700 years, to carbon 12. This loss of C14 balances the production from cosmic rays, and the C14, under normal conditions, maintains a relatively constant, low presence in the atmosphere. Once this C14 is removed from the atmosphere -- for instance by photosynthesis, into the living tissue of plants or subsequently of animals -- it continues to revert to C12, but there is no replenishment of the C14 by cosmic rays as there is in the atmosphere. This is the basis of carbon dating where, by estimating the proportion of C14 in a carbon sample, we can tell how long ago that carbon was removed from the atmosphere.

But sunspots introduce another factor that upsets the average conditions. They interfere with the Sun's emission of cosmic rays, so that when sunspot counts are high, there is less formation of C14 in the atmosphere.

Examination of tree rings formed during the Little Climatic Optimum, show a low level of C14, the result of the low cosmic ray emission -- ie, of the high level of sunspots. Thus, the high temperatures of that period have become associated with the high level of sunspots. Again, the high C14 count in tree rings, confirms what Man knew at the time of the Dickensian Winters of the low sunspot count, and the complete absence of sunspots during the Little Ice Age.

Thus Man has learnt that the effective energy from the Sun varies at different stages and that the "Solar Constant" is not as it was traditionally supposed to be -- not as the climate models have assumed it to be.

This natural effect of sunspots (together with the temperature-reducing effect of temporary dust veils thrown up by volcanic activity) can explain away the major temperature variations which might otherwise be incorrectly attributed to Man's activities. Forget all this nonsense of Man-made global warming -- the culprit is Nature and there's not a thing that Man can do about it.

Peter A. Toynbee, Wellington