Earth is the the pot, the atmosphere is the water, and we're the frog. The water has been gradually warming for the past 150 years. Simple physics tells us how fast the water is heating and when the water will boil. It's not a doomsday cult - it's forethought. The irony is forethought is something humans seem to be able to do pretty well on an individual basis but can't do in large populations. I defer to the anthropologists as to why that is.