Abstract
Abstract. Visible satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic sea ice reaches its minimum annual extent and the Antarctic sea ice reaches its maximum. 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. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three-week period. 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. 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. These early satellite data put the recently observed record into a longer-term context.
Highlights
The decline of Arctic sea ice extent over the past 3+ decades is one of the iconic indicators of climate change, culminating with a record low minimum extent in September 2012
The primary source of these sea ice extent estimates is a series of multi-channel passive microwave radiometers, the Scanning Multichannel Microwave Radiometer (SMMR) aboard the NASA Nimbus-7 platform and a succession of Special Sensor Microwave/Imager (SSM/I) sensors on US Department of Defense Meteorological Satellite Program (DMSP) satellites
The process of creating Arctic and Antarctic extent maps began with recovery of the data by the NASA Goddard Space Flight Center (GSFC)
Summary
The decline of Arctic sea ice extent over the past 3+ decades is one of the iconic indicators of climate change, culminating with a record low minimum extent in September 2012. The primary source of these sea ice extent estimates is a series of multi-channel passive microwave radiometers, the Scanning Multichannel Microwave Radiometer (SMMR) aboard the NASA Nimbus-7 platform and a succession of Special Sensor Microwave/Imager (SSM/I) sensors on US Department of Defense Meteorological Satellite Program (DMSP) satellites. In the Antarctic, the situation is more complicated with overall increasing trends in hemispheric sea ice extent, but with large interannual and regional variability
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