When I was in 4th grade my Weekly Reader at school proclaimed the coming of the next ice age. The teacher explained that the earth was getting colder and someday we would need winter coats year round. I remember being upset about this because who wants to wear their winter coat during summer vacation? By the time I graduated high school the New Ice Age had passed and we were now worried about global warming.
When Mt St Helen erupted scientists told us that the ash would remain in the atmosphere for years blocking the sun's warmth from reaching the ground and lowering the surface temps, didn't happen. When the Iraqis lit all the oil fields on fire in Kuwait similar claims were made. Again they didn't pan out.
Alarmist claims like global warming, global cooling or asteroids hitting the earth are necessary if you have any hope of getting a research grant. All you have to do is follow the money.