Why has the Arctic been a lot warmer than it is today?

They do not. They have taken the cart before the horse and proclaimed a theory, now they are trying to corroborate the theory and they cannot. Yes you are correct, the northern hemisphere was much warmer and the reason they have found large dinosaur fossils in Montana for example. The permafrost is saturated with frozen roots where once this land was a metropolis of vegetation.

It is a natural cycle, why is that so hard to believe for the liberal radicals. Why? because they can now make money off of this.

Looking for back into the history of the earth, tectonic movement (movement of earth's crust) is likely, in the past Australia was freezing wastelands, and Africa and the Middle East have been thick rainforests in the past (hence oil, gas and coal reserves in the Middle East).

Its hard to argue that the Arctic was ever warmer, being an Ocean, but evidence from Greenland suggests that it was once covered in thick carnivorous forests (trees which loose leaves in winter). As suggested, this may be due to tectonic movement.

There are however some other reasons;

1. Strong Air currents dragging warm air from the south, enough to keep the land warm enough to produce forest and tundra

2. Natural Temperature fluctuations, caused by perhaps differences in the earths tilt, (the earth 'wobbles' over millions of years, changing which North actually is)

3. Different shapes of land mass, in the past all the earths land has been in one area, in a super-continent, this would mean a continental climate effected everywhere. (for example if the UK were joined to europe by the removal of the english channel, then we would have hotter summers and cooler winters, simular to that of France) - a continental climate would allow warm air to travel across the land to the arctic during summer.

Hope this gives some indication.

This is why Scientists are so sure about AGW and the resulting climate change.

http://www.aip.org/history/climate/rapid.htm

http://www.scientificamerican.com/media/pdf/2008-1...

'casuse of global warming, the co2 on the atmosphere produced by pollution, it let the rays of the sun pass but not to leave the atmosphere it is like a big greenhouse to increase the temperature

you could visit these sites:

en.wikipedia.org/wiki/Global_warming

www.globalwarming.org

Well it was obviously Neanderthals and their carbon-based campfires.

Either that or dinosaur farts.