1) Natural CO2 levels tend to follow, temperature change, they do not lead temperature. (due to release of CO2 from hydrates & dissolved CO2 in the oceans, increasing biomass, etc.) CO2 is an effect of temperature excursions in the atmosphere not a cause of such.
Precisely why it is so difficult to determine the climate response to increasing atmospheric CO2 at the current rate. There are no paleoclimate analogs to this situation. (By the way, I don't know of any significant CO2 hydrates in the ocean, though they can form at depth from injected CO2. Methane hydrates, on the other hand, could be very signifcant.)
2) Much higher global temperatures with lower CO2 concentrations have existed in the past. CO2 concentration is poorly correlated with decadal & century changes in the climate.
Medieval Warm Period, or an earlier and longer epoch?
Merely calling CO2 is a radiative forcing agent in a model does not make it a cause of global temperature change manifested in the physical world.
As I noted earlier, the paleoclimate view of CO2 is a climate "thermostat" (whether or not you like the Gaia viewpoint). CO2 concentrations act to maintain either a warm or cold global climate.
As I noted earlier, the paleoclimate view of CO2 is a climate "thermostat" (whether or not you like the Gaia viewpoint). CO2 concentrations act to maintain either a warm or cold global climate.
In comparison to and in the presence of watervapor. It has a negligible role(inspite of The IPCC's redefinitions). I will admit that CO2 has a stonger role in the dry glacial periods where atmospheric H20 concentrations are much lower. The Oceans & ice caps have a much greater effect and capacity to act as a thermal buffer or "thermostat" than any concentration of CO2.
Take away water then you have a Martian or Venesian scenario, but as long as there is substantial open water on this planet, the role of CO2 is consigned to a marginal role at the very most.