One of the most reliable indicators of changing global temperature is the Arctic treeline – the northern-most latitude where it is warm enough for trees to grow. As climate warms the treeline advances north, and during cooling it retreats south. It is impossible for nonlinear-chaotic climate ever to be static and the 20th century is no exception: warming took place both early and late in the century. The Arctic treeline is a reliable record of this change. Nowhere is this treeline longer than in Siberia, Russia.
In this paper by Esper and Schweinburger 2004, the ebb and flow of the tree-line in the vast Siberian Taiga forest showed advances of the treeline during exactly the periods where the most rapid recent climate warming occurred: the 1940s and 50s, and then the 1970s.
But careful investigation of these 20th century tree-line advances revealed something important. Stumps of ancient trees coexisted with the regions of Arctic tundra which the recently advancing treeline had re-occupied. These ancient stumps were about a thousand years old. Their presence showed that this was not the first time that the Taiga had spread this far north. It had been there before, during the climatically hotter “Medieval Warm Period” (MWP) a thousand years ago. The treeline had since then retreated south during the colder centuries of the intervening “Little Ice Age” (LIA). With the natural warming rebound from the LIA, the Taiga treeline is just returning to the northward extent that it had previously occupied during the MWP a millennium ago.
Thousands of years ago a wise man wrote:
”What has been will be again,
what has been done will be done again;
there is nothing new under the sun.
Is there anything of which one can say,
“Look! This is something new”?
It was here already, long ago;
it was here before our time.
No one remembers the former generations,
and even those yet to come
will not be remembered
by those who follow them.”
Ecclesiastes 1: 9-11.