Over the last few years I have noticed blue spruce trees dying. It starts with the lower branches. The needles lose their color and drop. This continues up the tree, usually quite rapidly, and suddenly there are no needles left. I want to say the whole process runs its' course in three years or less, sometimes in a single growing season. Lower branches that are shaded will naturally drop needles over time, but if you see needles dropping on lower branches growing in the sun that used to be full and dense with needles, that tree might be next. I found this credible and recent article for more information. If you or someone you know has blue spruce trees, keep an eye on them. The best way to deal with this is to avoid planting these trees. It is always best to plant more than one species. If you need a replacement or want to plant a screen or barrier, use a mix of evergreen species.