I've heard a meteor, a wobble of the earth's axis, and on and on. This is a new one so far as I know.


"University of California scientists think they know why Earth’s generally warm and balmy climate over the past billion years has occasionally been interrupted by cold snaps that enshroud the poles with ice and occasionally turn the planet into a snowball.The key trigger, they say, is mountain formation in the tropics as continental land masses collide with volcanic island arcs, such as the Aleutian Islands chain in Alaska.
Earth’s climate is, to a large degree, driven by the amount of carbon dioxide in the atmosphere, which traps heat and warms the planet. While fossil fuel burning since the Industrial Revolution has driven CO2 levels to heights not seen in 3 million years, CO2 levels have been even higher in Earth’s past, coinciding with warm periods when no major ice sheets existed.
In fact, Earth’s default climate seems to be warm and balmy. Periods with no glaciers dominated for three-quarters of the past 1 billion years.
Yet, half a dozen ice ages chilled Earth during that time, two of them severe enough to turn the planet into a Snowball Earth with ice covering much of the surface. What caused these frigid interludes?
In a study appearing in this week’s edition of the journal Science, the team concludes that when volcanic arcs collide with continents in the tropics — an inevitable consequence of the planet’s constantly moving tectonic plates — they trigger global cooling, resulting in a glacial climate with extensive ice caps."