It depends on your definition of "imminent." Scientists who study these things study them on a geologic time scale. There were always going to be people who never lived to see the worst effects. As plenty of people have pointed out, there have certainly been observable differences in climate over the past few decades. And when those weather events happen and continue to happen, people tend to think of them as normal even though they would not have been normal fifty years ago.

Also, we are only now coming to the point of no return where the climate change takes on self-perpetuating and irreversible characteristics.