Assuming this is true (impact of climate change on ice melt if targets are not met), and given that no target established to date has been met, what is the level of confidence that current or future (rebaselined) targets can be met?  

Even if GHG emission intensity is reduced significantly, the global population is still growing and the monetary system requires near continuous economic growth.

Despite the low likelihood of success, and assuming governments will intervene anyway, the best policy appears to be Michael Chong's revenue neutral carbon tax, which provides predictability and a market based approach while eliminating wasteful program overhead, and getting the government out of the business of picking winners.