The dinosaurs were probably made extinct in half an hour. The dust that was injected into the atmosphere lasted about a year, blocking out sunlight and causing a drop in temperature. The whole chain of food production stopped. Like a nuclear winter. I would not use the term alarm.
Concern is a little more like it.
We don't know of any object heading toward the Earth right now, and the chances that there will be a catastrophe next year are quite small. But it would be prudent to carry out a survey and see if there really is anything headed our way. Actually watching 20 pieces of a comet crash into Jupiter and seeing the dramatic effects of those impacts was a sobering thing for scientists and should be for lay people as well. There are about 50,000 pieces that are 300 meters in size, the size of three football fields. There are some as big as 10 miles in size, and others in between.