7. Why should be the current climate change a threat for us if the climate has changed permanently in the past?
Climate is not changing for the first time. There have been fluctuations and changes in climate again and again over geological time. This might lead to the impression that current climate change is a recurrent, harmless event in (Earth) history.
On the other hand, paleontological evidence suggests that major changes in climate are associated with ecological catastrophes, including mass extinctions. Every species has its own climatic window it can tolerate. If it is getting warmer or colder, many individuals of a species might die and species have to either successfully relocate or go extinct. Extinctions might also happen due the unforeseeable new interactions between those species that can find habitat in the new world. In the oceans, other results of climate change, such as acidification and anoxia might have devastating consequences for the biota.
Due to human activities, climate warms at a previously unprecedented rate. This leaves even shorter time for ecosystems to adapt to the physical changes of the environment than what we observed in the fossil record. Based on this, there is a considerable chance that the current climate change will provoke a mass extinction which can destroy our existence and livelihood that depends on the healthy ecosystems.