In a new study that may greatly add to our understanding of the drivers behind climate change, researchers from Lund University in Sweden claim to have accurately reconstructed solar activity levels during the last ice age. By analyzing trace elements in ice core samples in Greenland and cave mineral formations in China, the scientists assert that regional climate is more influenced by the sun than previously thought.
The effect of the sun on natural climate change has been one of constant debate, and its degree of influence varies dependent upon the climate modelling used. However, this recent study by Lund University may suggest that direct solar energy input affects parts of the atmosphere which then indirectly changes atmospheric circulation, resulting in increases or decreases in temperature over certain regions.
According to the researchers, a measurable variance in solar activity during the last glacial maximum (22,500 - 10,000 years ago) resulted in increased winter precipitation during periods of low solar activity. The team claims that these results may explain the positive correlations between their solar activity reconstruction and the study of indicator isotopes they used as a measure of historical precipitation temperatures in the examined ice cores.
"Reduced solar activity could lead to colder winters in Northern Europe. This is because the sun’s UV radiation affects the atmospheric circulation. Interestingly, the same processes lead to warmer winters in Greenland, with greater snowfall and more storms." said Dr said Raimund Muscheler, Lecturer in Quaternary Geology at Lund University. "The study also shows that the various solar processes need to be included in climate models in order to better predict future global and regional climate change."
Further to their theory, the researchers believe that changes in wind patterns resulted from alterations in received temperatures, suggesting that a top-down solar influence increased oceanic feedback and may have acted as an additional amplification mechanism. In other words, variations in solar radiation affected the atmosphere, altering the barometric pressure which, in turn, changed the prevailing wind patterns in the upper atmosphere.
In atmospheric physics parlance, these winds are known as eddy-driven jets and a high-pressure increase over the North Atlantic (as evidenced in today's climate) is often accompanied by a displacement to the south of these winds. This results in a negative effect on the North Atlantic Oscillation (the atmospheric pressure difference at sea level between the Icelandic low and the Azores high), which can produce colder winds and higher levels of snowfall.
As a result, the alteration of these winds changes the way in which heat is exchanged between the oceans and the atmosphere. In the Lund University reconstruction and modeling, evidence is shown that this particular effect was being exacerbated by the amount of solar energy striking the Earth's atmosphere in direct relationship to the activity of the sun.
"The study shows an unexpected link between solar activity and climate change. It shows both that changes in solar activity are nothing new and that solar activity influences the climate, especially on a regional level," said Dr Muscheler. "Understanding these processes helps us to better forecast the climate in certain regions."
The upshot of all this is that the team claims that these results provide a testable theory for an alteration of current orbital sun/climate hypotheses, as the position and strength of the eddy driven jet is, along with other influences, proven to be related to orbital forcing (the effect on climate of slow changes in the tilt of the Earth's axis and shape of the orbit).
As such, the scientists believe that this indicates that changes in solar activity influence the climate, particularly at a regional level, and that the variations in the sun’s output also influences the climate irrespective of whether the planet is largely mild as it is today, or in the grip of an ice age.
The results of this research have been published in the journal Nature Geoscience
Source: Lund University
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