But what about the polar bears?

The foundation of Science is good measurements that can be independently verified. Consider the following two charts on historical temperatures:

These two charts could hardly be more different and yet both are produced by Climatologists who stand behind their accuracy. The first shows that we have climbed quite a bit since 1600 but that was an extreme cold dip;  AND our current high is less then 1100 BC before the carbon crisis AND we seem to be on a downward dip since 1998.

The second chart is the famous hockey stick graph cited by Al Gore in his documentary as proof of modern global warming. Wikipedia has a detailed discussion on it at http://en.wikipedia.org/wiki/Hockey_stick_controversy

Bottom Line

The wiki article cites many recent papers as supporting the hockey stick with results like warmest in the past 400 years or warmest in the past 600 years. But this is only proving that it's warmer than the start of the "Little Ice Age".  Temperature data older than this is still rather fuzzy but getting better with ice cores, etc.

So it may be fair to say the question is still open. What caused the Medieval warming period of 1000 years ago? Why is the modern warming different? or is it?