I don't think there were many humans 300 million years ago. What happened to the masters of the Earth from that time? Here's a hint: you can see them only in museums now. The last graph from your "Wiki" link shows something interesting: in the last 10,000 years, the period in which humans made their most dramatic progress, and spread throughout the world, invented languages, mathematics, engineering and so forth, the worlds temperature has been very stable, and cool. That is, until the last 150 years, that correlates perfectly with the beginning of the industrial revolution. During that period, fossil fuels began to be used for the first time in Earth's history. The graph from that period forward only goes up. And the closer to our present time, the faster the graph rises.
Global warming makes sense, not just from a historical standpoint, but also from a physical standpoint. The occurrence of other phenomena that affects Earth's temp does not mean that these effects, man made, cannot produce a change. A younger Earth, with much more volcanic activity and more acidic atmosphere has little in common with Earth today..Once one understands the principles involved, then he can see more clearly how this activity is affecting our climate, and how this correlates perfectly with historical data. The data confirms the theory; our activities are clearly affecting a change in global climate.