High Quality Content by WIKIPEDIA articles! The Last Glacial Maximum (LGM) refers to a period in the Earth`s climate history when ice sheets were at their maximum extension, between 26,500 and 19,000–20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and Asia. These ice sheets profoundly impacted Earth`s climate, causing drought, desertification, and a dramatic drop in sea levels. It was followed by the Late Glacial Maximum.