Right now, we don't know the exact percentages from natural and human contributions.
Yes and no. We have multiple glaciation cycles we can look at, and CO2 seems to top out at around 300 ppm during the warm interglacial periods.
We were also at that maximum prior to the Industrial Revolution. In just 150 years we have gone from 300 ppm to nearly 400 ppm, a level of atmospheric carbon dioxide never seen in the ice cores. We have also seen a change in the carbon isotope makeup of that atmospheric CO2, and it matches the ratios found in fossil fuels.
I would call that extremely strong evidence that humans are the cause for the spike in atmospheric CO2 over the last 150 years. Is all of that extra CO2 from the burning of fossil fuels? Probably not. There are also feedbacks that would release other naturally occuring resevoirs, such as an initial increase of CO2 causing the oceans to warm and release more CO2. Nonetheless, our role seems to be obvious to me.
I was under the impression that if all of the ice on land melted then the seas would rise by about 200ft or 60m.
I don't know the exact amount, but it is definitely going to go up. The ice is 2 miles thick on Antarctica, and I think Greenland has even more ice, even if it is a bit thinner at 1-2 miles thick. Sixty percent of the world's fresh water is tied up just in the Antarctic land ice.
Latest figures I saw were that close to 50% of all humanity lives within 50 km of ocean with most of that below 150 m.
In a bit of a paradox, AGW may have cancelled out the next glaciation cycle. While we may lose major population centers along the oceans, we may save other population centers from being destroyed by glaciers in the more distant future. I'm not trying to say that AGW is a good thing by any stretch of the imagination, but perhaps there is a bit of silver lining in the oncoming storm.
One of the benefits of trying to reduce our role in AGW is that we are realizing the limits of fossil fuels. If we keep using fossil fuels at current rates we are going to run out. This is reason alone that we need to move ourselves off of fossil fuels in addition to AGW.
What this tells us is that our ability to make decisions as a group is so hopelessly inadequate to the task at hand that we will carry right on until half of us drown and the other half starve.
There is something to be said for an authoritarian government. At least something moves forward, even if it is in the wrong direction at times. It is no wonder that the French overthrew their king only to turn around and give it over to Emperor Napoleon.