What is scary about global warming is that frozen ice in the poles might liberate dangerous bacterias, microbes and micro-organisms that were frozen for an extremely long time, and that might cause very important damages to humanity if we don’t act on it. May Allah protect us all.The existence of viruses and bacteria in the permafrost regions is nothing new. And it's not scary either. Thousands of viruses are being discovered, but so far about 83% are bacteriophages. They infect bacteria and not humans.
What should really scare you is this: Humans, although they know better, are acting completely against stopping climate change. They are really doing everything they can to let climate change progress rapidly. In my eyes, that is suicide. That really worries me.
To come back to the actual question:
I can certainly imagine that a virus that can destroy large parts of humanity is possible. I can well imagine zoonoses. When viruses, bacteria, fungi, etc. come between animals and humans, I think it can lead to dangerous situations.
And this is another area where climate change plays a role. Because this also changes habitats for viruses etc...