[morpheos137]

often food chains are actually more of food webs. Most species, especially humans, are adaptable as their environment changes. Look at polar bears. They started out as normal brown bears. Then during the ice age they developed polar attributes, like white fur and maratime diet. If the climate in the arctic warms they will move inland again and likely merge with existing brown bear populations in the taiga. Those that don't adapt will die. That is how evolution works and always has worked.

In the past the environment has changed very rapidly at time. All life eventually dies. That which endures longer is that which adapts.

A warmer more carbon rich atmosphere has some benefits:

Expanded arable regions, fewer droughts, more rainfall, more carbon for plants to grown (try turning all your carbon in the atmosphere into rock and let me know how life fares then.)

Carbon based life needs CO2. They have done experiments where a forest is subjected to increased CO2 ppm by plumbing and nozzels. It grew faster and more robustly. Life also needs warmth. During the Eocene epoch some 50 milion years ago the Arctic was sub-tropical and teaming with life.