Intelligent life during the ice age, and the carbon cycle; the sun as a red giant

Now, our Earth is probably not as hospitable as we think of it. There are extreme events which happen HERE approx. every 100,000 to tens of millions of years, such as the ice age. We do not have to worry about these events, obviously... however, on other Earthlike planets, these situation may also exist. There is a theory on what happens to intelligent life after such an event. First, if the ice age lasts for a considerable amount of time, this will likely (and ironically), lead to the build up of greenhouse gas. Then what would an ice age mean for a society? That is, would we still be emitting carbon into the air? If so, our oxygen levels would slowly deteriorate... as a result, our biology might be different after some time. Our red blood cell counts would rise and we would grow shorter. As grim as this might sound, this is rooted in scientific fact. Consider Earth at least 300 million years ago. Higher levels of oxygen led to animals that were much larger than today's. Fireflies grew even up to two feet in diameter. So, if we are ever faced by an ice age, or a supervolcano, any life that survives will become smaller. Our lungs will- literally- get smaller. And then, after the ice age, plant life will likely flourish as a result of the high carbon levels. What exactly happens to the composition of the air in this case is pretty much anyone's guess; Would plant life start growing faster than it did before the ice age? Just another thing that one might think about.
Now, besides the increase in carbon, there is also the question, which I've discussed before, about what the cycle of ice ages means when the sun is changing it's phase to a red giant!