A review of climatic history following a new look at Antarctic ice cores
One of the problems with long-term climate research is that we know so little and what might seem so obvious, sometimes is simply not the case.
Researchers have reconstructed temperature fluctuations in Antarctica for the last million years by studying ice cores. Up until now the presumption has been that these fluctuations were triggered by the global effect of climatic changes in the northern hemisphere.
In the current edition of the journal Nature, three physicists at the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association (AWI), Germany's largest scientific organisation, have presented new calculations on the connection between natural insolation and long-term changes in global climatic activity.
This new study is part of an expansion of the prevalent theory regarding the development of ice ages and shows that major portions of the temperature fluctuations can be explained equally well by local climate changes in the southern hemisphere.
It was around the middle of the nineteenth century that it first became recognised that much of Europe was at one time covered by a great ice sheet, but it was not until 1911 that a Serbian mathematician, Milutin Malankovitch decided to chart the ice ages of the Pleistocene.
Without the benefit of computers, all of his calculations had to be done manually and he spent the next 30 years working on them. He studied the effects of the tilt of the Earth's axis and the small orbital changes caused by gravitational pull from nearby planets at various times going back 600,000 years. This enabled him to create charts and tabulations of incoming solar radiation across the Northern Hemisphere.
Although Malankovitch's calculations are still used today, they have always been the subject of debate. Malankovitch generally felt that insolation changes in the Northern Hemisphere were of outstanding importance for climate change over long periods of time. Since numerous climate reconstructions based on ice cores, marine sediments and other climate archives appear to support this view, it has become the prevailing working hypothesis in current climate research.
The three physicists from AWI have made a further in-depth analysis of the temperature reconstructions in Antarctic ice cores. For the first time they took into account that winter temperature has a greater influence than summer temperature and. when this is done, temperature fluctuations reconstructed from ice cores can be explained by local climatic changes in the southern hemisphere.
Up until now scientists have always tried to explain historical climate data in the context of Malankovitch's classical hypothesis, ''… and to date,'' says AWI scientist Thomas Laepple, ''it hasn't been possible to plausibly substantiate all aspects of this hypothesis, but now the game is open again and we can try to gain a better understanding of the long-term physical mechanisms that influence the alternation of ice ages and warm periods.''
However, the researchers were anxious to point out that their work involved natural changes that take place over thousands of years and do not relate to potential climate change resulting from man-induced greenhouse gases.
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