This indicator tracks the extent of sea ice around Antarctica.
Figure 1 shows Antarctic sea ice extent from 1979, when routine monitoring by satellites started, to early 2016. Sea ice extent is defined as the area of ocean where at least 15 percent of the surface is frozen. This threshold was chosen because scientists have found that it gives the best approximation of the edge of the ice. Data are collected throughout the year, but for comparison, this indicator focuses on the months when sea ice typically reaches its minimum and maximum extent. February is typically when the sea ice extent reaches its annual minimum after melting during the spring and summer. The ice typically reaches its maximum extent in late September or early October after winter freezing, with the largest monthly average extent occurring in September. Data for this indicator were gathered by the National Snow and Ice Data Center using satellite imaging technology and data processing methods developed by the National Aeronautics and Space Administration.
Unlike EPA’s Arctic Sea Ice indicator, this indicator does not show the age of Antarctic sea ice. This is because nearly all of the Antarctic ice melts every summer, unlike the Arctic, where a large portion of ice survives for multiple years.