Tree Ring Study Shows Signs of Reversing Arctic Cooling
31.07.2010 - Atmosphere & Space, Flora & Fauna, Arctic
While some parts of the Arctic have cooled over the past century, overall temperatures have seen a steady rise since 1990, according to a summer temperature reconstruction for the past 400 years. In their study, which was published in the journal Arctic, Antarctic and Alpine Research, scientists from the Institute of Geography in Moscow, the University of Hohenheim in Stuttgart and the Helmholtz Centre for Environmental Research (UFZ) showed that while solar activity may have been one of the major influences in determining summer temperatures, this has been overlaid by other factors since 1990.
For their study, the German and Russian researchers analyzed tree growth using pine tree rings from Russia's Kola Peninsula and compared their findings with similar studies conducted in other parts of the Arctic. They studied wood samples from a total of 69 Scots pines (Pinus sylvestris) from the Khibiny Mountains on the Kola Peninsula, situated between the Arctic Circle and the ocean port of Murmansk. The region, which marks a transition between Scandinavia and Eurasia, is strongly affected by the Gulf Stream and North Atlantic Current, which makes it particularly interesting for climatological studies.
The researchers measured the width of the tree rings, using meteorological data from the past 127 years to calibrate the data. From this they reconstructed the summer temperatures on the Kola Peninsula and compared their results with similar tree-ring studies from Swedish Lapland and from the Yamal and Taimyr Peninsulas in Russian Siberia. They found that all the reconstructed summer temperatures over the past 400 years - whether from Lapland, the Kola, or the Taimyr Peninsula - show a temperature peak in the middle of the 20th century followed by a 1-2°C cooling.
The researchers noted, however, that the reconstructed minimum temperatures coincided exactly with times of low solar activity, which led the researchers to conclude that, in the past, solar activity had a significant impact on summer temperature fluctuations in the Arctic. Yet the team also found that this correlation is only visible until 1970, after which other factors started having greater influence.
As tree growth can be strongly influenced by non-climatic factors such as light, nutrients, water supply and competition from other trees, it was vital to isolate these trends to obtain as pure a climate signal as possible.
