There are currently only two major ice sheets in the world, located in Greenland and Antarctica. These ice sheets are remnants of the Pleistocene Ice Ages, when much of the Northern Hemisphere was covered in ice sheets. The largest store of permanent ice is found in the Antarctic Ice Sheet. Data from NASA's satellites show that there has been a decline in land ice in both Antarctica and Greenland, contributing to global sea level rise. Researchers are now studying the future mass balance of these ice sheets. In comparison to the two current ice sheets, during the Last Glacial Period, the Laurentide Ice Sheet covered much of the Northern Hemisphere.