Here’s a good comparison: the asteroid that killed the dinosaurs, which was around 15 kilometers (9.3 miles) across unleashed the same amount of energy as roughly 100 million tonnes of TNT. That sounds like a lot, but it’s nothing compared to Shoemaker-Levy 9, the comet that hit Jupiter in the early 1990s.
This comet, which was originally “just” 5 kilometers (3.1 miles) across broke into multiple fragments. The largest fragment, G, slammed into Jupiter on July 18, 1994 at such a remarkable speed that this impact alone was 60,000 times more powerful than the asteroid that ended the age of the dinosaurs.
Swift-Tuttle is not only moving at typical comet speeds, but as aforementioned, it’s also quite sizeable. If it hit us, the energy unleashed would be around 10-28 times that of the dino-killing asteroid impact. It’s no Shoemaker-Levy 9, but it’s still catastrophic.
If you’re feeling glum about our prospects, then here’s the good news. The odds of it even hitting Earth during each orbit, interfering Jupiter or no, is one-in-500,000.
That makes it more likely than Yellowstone supervolcano erupting in any given year in some form of another, but here’s a strange stat to end on: if you’re American, you’re 14 times more likely to be run over by your own lawnmower than you are to see Swift-Tuttle wipe out humanity. So, all in all, we would advise enjoying the annual meteor shower and not worrying so much about space-borne killers.