The average G-type star shows a variability in energy output of around 4%. Our sun is a typical G-type star, yet its observed variability in our brief historical sample is only 1/40th of this. When or if the Sun returns to more typical variation in energy output, this will dwarf any other climate concerns.
The emergence of science as a not wholly superstitious and corrupt enterprise is slowly awakening our species to these external dangers. As the brilliant t-shirt says, an asteroid is nature's way of asking how your space program is doing. If we are lucky we might have time to build a robust, hardened planetary and extraplanetary hypercivilization able to surmount these challenges. Such a hypercivilization would have to be immeasurably richer and more scientifically advanced to prevent, say, the next Yellowstone supereruption or buffer a 2% drop in the Sun's energy output. (Indeed, ice ages are the real climate-based ecological disasters and civilization-enders -- think Europe and North America under a mile of ice). Whether we know it or not, we are in a race to forge such a hypercivilization before these blows fall. If these threats seem too distant, low probability, or fantastical to belong to the "real" world, then let them serve as stand-ins for the much larger number of more immediately dire problems whose solutions also depend on rapid progress in science and technology.
Via "2013 : WHAT *SHOULD* WE BE WORRIED ABOUT?" at Edge.org.There's no direct link to the essay I've quoted; search for the essay title "Unfriendly Physics, Monsters From The Id, And Self-Organizing Collective Delusions" on that page.