Global Warming?

I'm a little skeptical about global warming, not that I don't believe it
is happening, but maybe the warming is just a natural part of the
earth's climate cycle. In the history of earth there were rain forest
in Antarctica and glacier covering most of the northern hemisphere, but
let's just look at the past 2000 years.

In the first century AD the Romans invaded Britain to colonize it, at
that time they brought grape vines with them, and for the next 1200
years wine was produced there.

There was a period of time in the 6th century there was a slight cooling, caused
by a volcanic eruption of the Krakatau caldera in Indonesia.

Shortly after this the earth entered a warning period, know as the
"Medieval Warming Period". This lasted approximately from the 6th to
the 11th century. During this time, the North Atlantic became free of
ice. The Vikings sailed to and colonize Greenland, Greenland because it
was green. There was an abundance of birch trees around the fjords in
there, They went to Labrador and Newfoundland, where they discovered
wild grapes growing. All of Europe experienced prosperity and growth.

Sometime in the 12th century the earth enter the what is referred to as
the "Little Ice Age". It was estimated to last into the 19th century, During the
period of time Europe went into decline, the growing regions for grapes
move 300 miles south to France, Famine became common. The colonies in Greenland and Vinland were abandoned, There is speculation that the climate lead to the spread of the black
death, since people seemed more inclined to huddle in their hovels with the rats. The only good about this period in northern Europe, was the making of more beer to replace the wine that wasn't being produced.

So now it's getting warmer, wine is returning to Britain, and some of ice in the north is going away. Is man causing this or is it part of a nature cycle?