Regardless of that non scheduled theology.

Grain was grown, IN Greenland, for several hundred years.

Which IS NOT POSSIBLE presently.

And hasn't been for many hundred years since.

Meaning,

despite any Go West Young Man propaghanda,

Grain was grown:

or they could not have sustained themselves therein for those several hundred years.

Further, that grain was grown is a fact. It is not a model, a theory, a postulation or wishful thinking.

Therefore! That portion of the northern hemispheres atomosphere was warmer than presently; without benefit of the modern improvements in communications and transportation to blame(or more importantly, to use as an anthem for carbon taxation, it's related scams and of course the tyranny inherent therein).

And btw, CO2 is something humans exhale and plants inhale. Forgive me if I extrapolate incorrectly, but it seems to me that CO2 is a life giving gas that escapes our atomosphere. Another proven fact, is that plants will grow better if the CO2 content of their environment is increased by as much as 300%.

Gotta go for a drive.