Here's the evidence on ice thickness in the Arctic:
(click on image for link)
We had about 1,000PPM when there was no ice at all anywhere on Earth. Carbon dioxide levels started dropping when we reached the arrangement of the continents that we have now.
The facts show that Antarctica started freezing up at about 450PPM (or a bit higher?). This was about 40 Million years ago. Carbon dioxide got as low as 170PPM during the ice ages. Carbon dioxide has stayed between 180PPM and 280PPM over the 200,000 years of human history:
...EXCEPT in the last 150 years or so. We passed 300PPM in about 1904 or thereabout. Now we are at 389+ and climbing fast. Do we want to wait and see what happens when we go past 450PPM?
Oh and Lord Monckton is not a particularly reliable source:
http://politifact.com/truth-o-meter/...en-treaty-thr/