Sure it would help. Even during ice ages there were parts of the world that were warm and green. A greenhouse that was heated would extend the growing season just as they do now. RScott

Yes, I am using an unheated one right now to grow crops through the winter. With no additional heat I am restricted to cold loving crops like kale, arugula, lettuce, cabbages, carrots, radishes, etc.. If I went with a heated house I could grow about anything I wanted, though at a cost for fuel.

if you were to be in the ‘cloudy time’ that would precipitate the Ice Age, then you’d need not only heat, but light, as well….. since the sunlight would be much less due to the clouds…..