NASA: Four Decades of Sea Ice From Space
By NASA.gov // September 8, 2014
analyzing long-term behavior of the Arctic ice
ABOVE VIDEO: The study of Arctic sea ice changed forever with the dawn of the Space Age and the first Earth-observing satellites. Part 2 of our animated timeline picks up where Part 1 left off — with the launch of the TIROS weather satellite.
NASA.gov — By the end of last century, scientists had painstakingly developed and tested the remote sensing techniques that allowed them to monitor sea ice from space.
In the 1980s, the scientific community started becoming more interested in watching for signs of climate change in various Earth systems — but through that decade, sea ice showed very little in the way of clear-cut trends. The drastic changes of the past 15 years weren’t even imagined back then.
“It was like watching paint dry,” said Jay Zwally, a senior scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., one of a handful of scientists who began in the early 1970s intensively working with satellite imagery to study sea ice.
Still, the new data allowed researchers to start analyzing the long-term behavior of the Arctic Ocean’s icy cap.
One of the first studies to establish a trend of sea ice growth and retreat was written by Claire Parkinson and Donald Cavalieri, both at NASA Goddard, who in 1989 published an analysis of the data collected by the Electrically Scanning Microwave Radiometer (ESMR, launched onboard NASA’s Nimbus 5 satellite on December 10, 1972) and its successor, the Scanning Multichannel Microwave Radiometer (SMMR, which was sent to space onboard NASA’s Nimbus 7 satellite on October 24, 1978).
“By that time, in 1989, people were talking about global warming and its possible consequences, including effects on sea ice and other variables,” Parkinson said.
One problem in truly divining a trend was the lack of continuity – there was a two-year data gap in the 1970s between the ESMR data and the successor SMMR data, hindering researchers from connecting those two data sets. So Parkinson and Cavalieri examined the two records separately. As of 1989 they found some initial signs of sea ice decline from the SMMR data – but nothing that they could be certain was part of a long term trend instead of a natural cycle.
“We couldn’t be sure, with such a short record, the interannual variability in the ice cover, and such a small trend toward decreasing ice coverage,” Parkinson said.
“But the decrease we saw certainly was enough to alert us to the fact that we should keep up this record and continue to monitor the changes.”
A decade later, Parkinson, Cavalieri, Zwally, and their colleagues Per Gloersen and Joey Comiso, also at NASA Goddard, revisited the satellite data.
This time they added the measurements collected by the Special Sensor Microwave/Imager (SSM/I) instruments onboard satellites of the United States Air Force’s Defense Meteorological Satellite Program.
They noticed that the sea ice decrease not only had continued but also was far more convincing than it had been in 1989. In their 1999 publication, they were able to report that the Arctic sea ice cover had retreated at an average rate of 2.8 percent per decade.
“But during this period there were still some pretty wild swings, too,” said Walt Meier, a research scientist at NASA Goddard.
“There was a seesaw pattern: For example, 1995 was a record low year for the September sea ice extent. And then the next year was a record high in the Arctic.”
Further, they reported that the trend was negative in every season. Summer showed the largest ice loss at minus 4.5 percent per decade, or minus 14,788 square miles (38,300 square kilometers) per year – roughly the size of Maryland and Connecticut put together.
The trend scientists had been looking for was now clearly visible.
However, the scientific community did not foresee in the 1990s the accelerated decay of Arctic sea ice that lay ahead in the following decade.