Assuming no other action, how many Earth Hours do we need every year in order to avoid dangerous climate change?

Climate models assume that over time random errors will average out leading to meaningful prediction, similar to the distribution of heads and tails in a coin toss.  Can we make this assumption for a chaotic system?  Doesn't this imply we should also be able to create reliable long term models of global interest rates or currency exchange rates or any number of chaotic systems