The Diehold Foundation and other sites describe how roughly every 12,000 years there is a series of events that tend to disrupt the planet. The premise is that there is a galactic sheet of dust circling out from the center in a spiral.
Representation of Spiral: Source The Solar System passes through this sheet and it acts as a figurative heartbeat. In addition to causing magnetic reversals on the planets, it is suggested that it triggers various levels of the nova in the suns that pass through this cloud. To paint an image, imagine accumulations of snow on a roof or mountain. Once it reaches a certain threshold, an avalanche happens. In our case, followers of this conjecture suggest that roughly every 12 thousand years our sun has a micronova. This nova is characterized by first a wave of solar energy followed by a wave of ejecta a number of hours later.
Deposits of glass beads found on both the Moon and on Earth are being used as evidence of these events:
Their supposition is that the initial flash will boil off roughly 1000 feet of water (if it impacts the Pacific) causing a huge cloud blocking out the sun, as well as tsunamis which will quickly devastate all the (Pacific) coastlines. Additionally, as the planet rotates, other parts will be bombarded with projectiles from the sun. In addition to the microbeads of glass, there is a suggestion that the meteor impacts, 12,000-years-ago, precipitated the era known as the Younger-Dryas.
Source
This impact crater found underneath the Hiawatha glacier in Greenland has been suggested to be the main impact that has precipitated the renewed glaciation during the Younger Dryas period. Just as earthquake 9-years-ago moved Japan by about 8-feet, speculation is that impacts in the past may have even dislodged what is now Sri Lanka from India.
Another aspect speculated with this event, not only would there be an immediate and prolonged winter caused by the water first converted to steam, blocking the sunlight and in turn condensing and turning to snow but also a volcanic winter would be triggered. The Toba Catastrophe which occurred about 75,000 years ago (a suspected earlier micronova event) resulted in a volcanic winter lasting 6-10 years and promulgated a 1000-year cooling cycle. This event has been pointed to as the cause of the genetic bottleneck that happened around this time where humanity has been traced coming from as few as 1000 to a maximum of 10,000 breeding pairs.
While I cannot speculate on its veracity, the idea that this event may occur potentially in 26-years is very thought-provoking and raises the question: "What would you do?"