These color-coded maps compare sea ice age, the week of March 4, 2000 (left) and the week of March 5, 2023 (right). Oldest sea ice is white, and youngest sea ice is dark blue. The extent of old, thick sea ice in the Arctic has declined significantly since the mid-1980s, when satellite measurements first became available, and even since the start of the twenty-first century. — Credit: NOAA Climate.gov based on data from NSIDC