Here's a link of evidence of the effect of climate change:
Climate Change: Evidence
Specifically the ~8" of rise: 6.7" (in the previous century) + 2X that rate for the past decade = 6.7 + ((6.7/50) x 10) = 6.7 + (0.134 x 10) = 8.04
1. we are now gaining ~3ppm / year and this is going to likely increase as time goes on. As long as we keep burning fossil fuels at a rate of ~31 gigatons a year, it will go up at least as fast as it is now. If we reach a point where we get runaway melting of the tundra, which releases untold quantities of both methane (20X more "powerful" greenhouse gas) and carbon dioxide and/or the ocean starts to release carbon dioxide as warming increases - then all bets are off.
By the way, this last feedback forcing is what caused carbon dioxide to "lag" behind the warming in the past. The ocean water has been absorbing a lot of our increase of carbon dioxide up until now, but warmer water cannot hold as much carbon dioxide as colder water, so at some point it will begin to release it - and this will greatly accelerate the increase in the atmosphere - this could be the threshold that tips us into a runaway heating climate.
2) It depends on where we end up on greenhouse gases in the atmosphere. How hot is Venus? It has a huge amount of greenhouse gasses.
How Hot is Venus? | Space.com
Above 450ppm, it is likely that Antarctica will melt.
3) It again depends on how much greenhouse gasses are in the atmosphere, and therefor how hot it gets. If all the ice all over the world melts (which would take 1,000's of years probably) then the ocean level would be about 220 feet from Antarctica and Greenland and higher because of the temperature of the water.
HowStuffWorks "If the polar ice caps melted, how much would the oceans rise?"
4) This process doesn't end well - if it gets to hot and really acidic, and if the oxygen is largely driven out of solution, then the ocean will release hydrogen sulphide.
5) We are in a precarious place. As the graphic I posted earlier indicated, we are inevitably going to see 1.5C increase even if we stopped all fossil fuel burning tomorrow. We really need to stay below 2C in order to mitigate the worst effects, and squeak by... That means we cannot burn more than ~500 gigatons of carbon, and at our current rate, this is about 13 years. And that means leaving 4/5 of the known reserves *in the ground*. If we cut back a lot now, then we can stay under that "budget" over a longer time span.
If we can sink carbon, we need to do that. Biochar is one way, and letting forests regrow in large areas, and letting the major plains return to grasslands, and probably other methods of sinking carbon back in to the ground in a stable form, so it stays put. The natural weathering process is very slow. It took about 55 Million years for the carbon dioxide level to drop from ~1,000ppm down to the ~270ppm level where it stabilized for the 650,000 years leading up to humans showing up.
I know of nothing more important that we humans have ever faced. Since we have caused it - we can stop causing it, too.