It's been a long time since I've written anything on super flares. My last year at KU, this was my research topic, in which I was looking at some really big flares on some stars very similar to the Sun.
The thing about those flares is that, in the 200ish years we've been watching the Sun, we've never seen anything that's even close. So can the Sun do anything like those, because if it can, we should be worried. Very worried. A coronal mass ejection or flare of that size would wipe out the entire electrical grid of the world in minutes.
The biggest solar flare we know about, was the "Carrington event" in 1859. This one was large enough to cause currents in telegraph wires strong enough to start fires on the desks of the operators. Even when the batteries that powered the system were disconnected, telegraphs could still be sent. With a much larger system carrying much more energy that is much more stressed today, we'd be in far bigger trouble if that happened again.
So ideally we'd like to know more about how the Sun acts over a longer timescale. The professor I was working with on this was Dr. Melott, and this week he released a paper that looks at a way to look through the historical record for signs that other flares may have hit us.
One of the effects we'd expect is that we'd see a sudden spike in C14, the isotope of carbon used for radioisotope dating. This is created when high energy protons from the sun hit our atmosphere. Usually this is pretty stable, since the Sun is pretty stable on longer timescales.
Drilling ice core samples and looking at the C14 in air bubbles trapped in the ice provide a way to see how much C14 was being created. It turns out that there is just such a spike around 774-775 CE.
While it can't be confirmed that this was absolutely caused from the Sun (a nearby gamma ray burst could similarly irradiate our atmosphere causing the formation of C14, but it highly unlikely), it's still a good bet. If it was the case, it would have been an eruption with some 2x1026 J of energy!
This is still a bit shy of the super flares that were the focus of my research, but it's getting close. So it's not unrealistic that the mechanism that produced those flares could also happen to us. If so, it's not so much a question of if, but when.