Not to be negative about this but :-). When you take CO2 that was stored during a period of warmer global temperatures and release it back into the atmosphere over a short period of time you might expect a little warming. The complications arise over what is the background temperature and how much increase over that temperature can you expect. You also cannot be certain of what the effects of rising temperature may be. The real concern is that when you look at the geological record you see that there is a runaway effect evident with temperature change. The positive feedback is evident both in periods of cooling and warming.
So what are the dangers that we face if runaway warming actually takes place? I don't think that extinction rates are a very good measure of the dangers evoked by global temperature changes as they simply reflect the lag in adaptation. I don't think any serious climatologist actually thinks that warming will cause the extinction of the human species or the extinction of life on the planet. From a human perspective sea level rise, agricultural production, water resources, and air quality seem to be the main issues. That human should damage the environment "foul their own nest" like any other species during periods of excessive population growth should come as no surprise. I reject the false dichotomy of man and nature and prefer to think of the world as a garden and man as it's gardener. What we do to control the temperature in our greenhouse is let to be seen but careless management will undoubtedly produce loses. The technology that the "environmentalist" blame for unbalancing the greenhouse is ultimately the tool that the gardener will use to preserve life on this planet.