By use of satellite photos and field studies, the vegetation north of the 50th parallel has been studied thoroughly and compared with older data from the same area. The results are described as sensational by researchers and show that the effects of global warming are highly evident in the north.
Data from the study shows that the growth season in the northern parts of the globe has expanded with up to 40 days over the last 30 years.
“Norwegian climate and vegetation as we know it today might be totally changed within some decades. The same process is happening in Siberia, in Alaska and in the northern parts of Canada. Mountain plateaus become Forrest land and the winter period is shorter and shorter every year”, says Hans Tømmervik at the Norwegian Institute for Nature Research (NINA)
Tømmervik was the part of the Norwegian crew who participated in the international group of more than 21 researchers form 17 different institutions which have studied the changes over the last 30 years. The results were published in the report “Temperature and Vegetation Seasonality Diminishment over Northern Lands” which was published in the periodical Nature Climate Change earlier this year.
The warming of the Arctic regions leads to a shortening of the season change, with shorter spring and autumn periods. The climate of the north will in time become more similar to the climate we see in middle Europe today and vegetation will thus change in the same direction, according to the studies.
“If the warming continues we will have a situation in some years from now where it will be hard to separate the season from each other, like we see in middle Europe today”.
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Over the last 30 years the growth season has in average increased with 3-4 days per decade. However there are large variations between areas.
“These changes have been far more dramatic in the northern hemisphere than any other place on earth”, says Tømmervik.
He explains that the start period and the end period for the vegetation growth are very dependent on threshold temperatures. When the trends of these threshold temperatures change and thus change the start of the photosynthesis, it will in time change the vegetation.
“A special analyzis show that there is a strong link between changes of annual temperature in the north and the changes in the vegetation structure. Since the average temperature rice has been highest in the winter time, it has led to a gradual decrease in the difference between mean winter and mean summer temperature since 1982. In other words the differences between summer and winter have been reduced in this period”, says Tømmervik.
The reduced season variation is estimated to correspond to somewhere between 4 – 7 latitudes southwards for the Arctic areas.
“We have tried to run the data through 17 different models where we estimate that the changes will continue at the same pace. What these estimates indicate is that the climate in the Arctic might shift up to 20 latitudes south. If this scenario becomes reality the climate in the Nordic countries in 2100 would be more similar to what you see France today”, says Tømmervik.
The result is that trees and bushes will be able to grow where only lichen and heather was living earlier. Species move slowly towards the north and up into the mountain hills. The increased vegetation in the north also give an extra boost to global warming, and thus give an extra boost to the rapid changes.
And as the vegetation changes, insects and animals appear which earlier could not survive in the harsh climate of the north.
“In recent years we have seen in the north attacks on trees by insects and fungus which have not been seen so far north earlier. The consequences can be disastrous for the trees which are attacked”, says Tømmervik.