Steve McIntyre has pointed out a colorful article written in German in which German and Swiss scientists reconstruct the forest border in Alps. What have they found? Let me be brief.
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Figure 1: This is what you see today...
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Figure 2: This is what the Romans probably could have seen 2000 years ago: Green Alps. The forest goes up to the height of Tierbergli hut (2795 meters above the sea). In a few centuries, we may return to these conditions of a thriving Roman empire - if there will be warming - or not - if there will not be a sufficient warming. ;-)