The idea of a stable ecosystem is a myth. Yes, in hundreds of thousands and millions of years the region will change dramatically. The difference between natural variability and instability is the rate of change. If left to the "natural" cycles and instability of the earth's climate, you would see gradual changes over tens of thousands and hundreds of thousands of years.

What people like you don't understand is that our man made climate change is 100 to 1000 times faster than anything nature has dealt (except say a meteor hitting the earth).

So yes, the climate has always been unstable over long periods, but never changed as quickly as we are changing it today. We are the meteor now.