If the temperature does rise 0.5 or 1 degree, if the population does cross over the threshold, if the pollution does pass the mark, if the sea levels do rise by a foot or two... these all can result in catastrophic events, including mass extinctions.
What we are experiencing is the beginning stages of such state for planet earth. We as humans have been the "wild card" factor in this dynamical system, and we have royally skewed the bias. The earth will heal itself through acts of extreme aggression, however, whether we will survive to heal with it remains to be seen.
We could, if we already have not advanced that far, try to become more and more in tune with the natural world around us. We could attempt to re-think and re-imagine our past lives and routines, and we could make changes accordingly to align with the universal law. This is nothing noble or new, it's has been discussed and practiced by many people over the ages. All the apocalyptic stories in the scriptures and different cultures, including the myths of civilizations long lost, point to this destruction of man-made societies and empires in consequence of destructive habits, behaviour and events. The flavours are varied, but the symbolism of the tales represent the same concepts.
What is different now is the fact that we are being presented by the Final Warning. It may already be extremely late. It may already be a lost cause, but we could still make a difference. We could see the Light.
And to those who choose to go against the natural law, and ignore the Warning by being distracted by anything other than complete alignment with the natural forces: enjoy the poison of your rotting ego, and may Kali Ma bring forth your just end.