I read somewhere they used to grow crops in Iceland ( or it might have been Greenland) in areas that it is impossible to do so today.
Bolthead,
Nuuk the Capital city of Greenland is in the area settled by Eric the Red. Today in summer they grow grain and vegetables (even potatoes) to supply the city.
Today scientists think that the couple of Little Ice Ages that have occurred since 1300 were caused by volcanic eruptions .
If you're interested there is some interesting reading here.
https://www.scientificamerican.com/a...noes-affect-w/
This one is also good reading and may explain your trees under ice .
Volcanoes linked to cultural upheaval since early Roman times | ScienceNordic
Climate is not a static thing but change always has some cause.
Today there is no obvious cause to be seen for the changes happening other than man and his bolshie attitude that we can destroy the lungs of the earth (trees) while at the same time pump 50 gigatons of heat trapping gas into the atmosphere every year.
There are solutions but we have to act. The first thing to do is get rid of our current wishy washy politicians who can't even make a decision about a marriage act without spending $122 million.
How the hell will they ever be able to make big decisions?