As of Sept. 21, 2007, sea ice extent stood at 4.18 million square kilometers (1.61 million square miles), an increase of 50,000 square kilometers (19,000 square miles) compared to the value of 4.13 million square kilometers (1.59 million square miles) observed on Sept. 16, which appears to be the 2007 minimum. Credit: National Snow and Ice Data Center