What leads to the 'impact winter' following a major global impact event?

Global shroud of vaporized material and dust blocking sunlight.

Following a civilization-threatening impact, the immediate destruction gives way to a prolonged, planetary environmental crisis characterized by an 'impact winter.' This severe cooling is triggered by the sheer kinetic energy of the collision, which blasts vast quantities of vaporized material and fine dust high into the stratosphere. This material forms a global shroud around the planet that effectively blocks incoming sunlight for durations lasting months, potentially years. The resulting lack of solar energy halts photosynthesis entirely, leading to a swift collapse of the entire food chain from its base level upwards, causing global temperatures to plummet even near the equator.