Environment Counts | Satellite Arctic sea ice extent record extended back to 1964 :
Recently, the National Snow and Ice Data Center acquired stacks of 49-year-old film rolls from a National Climate Data Center storage facility in North Carolina. The film is from one of the first U.S. Earth-observing missions, the NASA Nimbus 1 satellite and were dated August to September 1964. The film contained the earliest satellite data of Arctic and Antarctic sea ice extent. The current satellite record of sea ice extent only goes as far back as 1978. Close to 40,000 frames were scanned and georeferenced to produce the first satellite maps of the sea ice edge in 1964 and an estimate of September sea ice extent for both the Arctic and the Antarctic.
Images from a three-week period were manually analyzed to estimate the location of the ice edge and then composited to obtain a hemispheric estimate. The Arctic 1964 extent is near the 1979–2000 average from the passive microwave record, suggesting relatively stable summer extents during the 1960s and 1970s preceding the downward trend since 1979 and particularly the large decrease in the last decade. The 1964 Antarctic extent is higher than estimates from the 1979–present passive microwave record, but is in accord with previous indications of higher extents during the 1960s.
