Ice core data from Greenland reveals something that challenges everything we think we know about climate stability. The evidence shows that during the last ice age, temperatures shifted from full glacial to interglacial conditions not once, but twice, and each transition happened in just three to five years. Not centuries. Not decades. Three to five years. The measurements come from annual ice layer thickness spanning fifteen thousand years, and the pattern is unmistakable. What caused these rapid shifts remains unknown. The mechanisms driving such extreme transitions are still not understood. But the implications are staggering. If a shift like that happened today, moving from our current interglacial state into glacial conditions over the span of five years, modern civilization would not survive it. The infrastructure, agriculture, and systems we depend on are built for climate stability. A return to ice age conditions in half a decade would collapse all of it. That is not speculation. That is what the data tells us is possible.