Arctic sea ice reached its annual minimum extent Sept. 19, and then again on Sept. 23, 2018.
NASA works with the National Snow and Ice Data Center to track sea ice in the Arctic as it grows to a maximum extent through the winter and shrinks back to to its minimum extent in September. This year’s minimum sea ice extent reached 1.77 million square miles -- tied as the sixth lowest sea ice minimum since consistent satellite records began.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0