Bastardi says:
In my opinion, most of the warmth today is likely natural given the tiny amounts of CO2 relative to the entire system, of which the oceans have 1000x the heat capacity and are the great thermostat of the planet, taking centuries of action and reaction to reach where they are now.
He doesn't mention the icecaps melting. lulz. Also, we get a lot of our oxygen from the oceans, just like with trees, so we need them to stay the same temperature.