The mass extinction at the end of the ice age was likely caused by a super solar flare.
Could something like this recur in the near future, as depicted in the 2009 movie Knowing?
There is evidence that at the end of the last ice age, during the Younger Dryas (13,000 to 11,600 years before 2000), the Sun was much more active than it as present and that it had released several super solar flares with associated super solar proton events. In fact, there is evidence that one such event, which occurred ~12,887 years b2k, was a climactic event in the Pleistocene megafaunal extinction. More information on this can be found in the following Starburst Foundation press release and in the paper "Evidence for a solar cause to the Pleistocene mass extinction," published in 2011 in the journal Radiocarbon. There are numerous reasons why this mass extinction was not due to a supernova and related impact of a volley of comets as suggested by Richard Firestone. Some reasons are mentioned in the above paper, others are summarized in the eprint paper "The cause of the megafaunal extinction: Supernova or Galactic core outburst?"
It is unlikely that the Sun, in its current state of activity, would produce a solar proton event of this magnitude. However, if a galactic superwave were to arrive and begin to impact our solar system the Sun could change dramatically. If this galactic cosmic ray volley were to persist for several centuries and inject a large amount of dust and gas into the inner solar system, it could substantially aggravate the Sun and cause it to enter a T Tauri-like flaring state similar to that which apparently prevailed at the end of the ice age.
In the absence of a superwave it is still likely that a moderately large solar proton event could strike the Earth, similar to the Carrington event that impacted in 1859. While a Carrington event would not pose a lethal radiation hazard, as did the Younger Dryas event, it could nevertheless create enormous voltage surges in the electrical grid, burning out step-down transformers, and rendering world-wide blackout conditions for years. Vehicle traffic would be severely impacted due to the inoperability of gas pumps in most fueling stations. Manufacturing would come to a halt, including the production of much needed pharmaceuticals. More moderate inconvenience would be the disruption of satellite TV and possible failure of cell phone networks. In March 2009, the U.S. National Research Council has issued a report that provides a general overview of the hazards that would accompany the occurrence of a Carrington event.
The solar proton event (or events) and associated conflagration that occurred during the Early Younger Dryas had a tremendous impact on human civilization. It may explain the 400 year lapse between the disappearance of Clovis Indian arrowheads and the apperance of Redstone PaleoIndian arrowheads. Apocalyptic conflagration myths, such as the ancient Greek myth of Phaethon as well as other such stories from around the world tell of the hardships that this event inflicted on our ancient ancestors. These stories are recounted in the book Earth Under Fire along with scientific evidence backing up the apparent reality of the described events. Often these legends relate the occurrence of a catastrophic flood immediately following the conflagration. As explained in Earth Under Fire, elevated temperatures during this super solar storm would have elevated temperatures in the polar regions sufficiently to have induced catastrophic meltwater discharges from the heights of the polar ice sheets. This could explain why well preserved carcasses of mammoths and other mammals have been found frozen in the arctic tundra in Siberia and Alaska.
Auroral displays resulting from major solar flare events witnessed by paleoIndians could explain petroglyph drawings found around the world. This is the theory proposed by Anthony Peratt of Los Alamos National Laboratory. In their article published in IEEE, Peratt, et al. (2007) report on an extensive body of data they have gathered from rock art sites around the world, where they show strong resemblances between these drawings and high-current z-pinch plasma-focus auroral displays. One plate from their paper is shown below.
1) LaViolette, P. A. Earth Under Fire. Rochester, NY: Bear & Co., 2005, 1997.
2) LaViolette, P. A. Galactic Explosions, Cosmic Dust Invasions, and Climatic Change. Ph.D. dissertation, Portland State University, Portland, Oregon, August 1983.