Disappearing sea ice and its impacts

Claire Parkinson, project scientist for NASA’s Aqua satellite mission. Among other things, this mission measures floating sea ice at Earth’s poles. She spoke with EarthSky about disappearing sea ice and its impacts.

Parkinson said:

Sea ice really does have quite a few impacts, both on the rest of the climate system and also on ecosystems.

Sea ice is ice that forms off in the freezing of seawater. It’s a very common feature in the polar regions. Sea ice really is quite an effective insulator between the ocean and the atmosphere. And also it’s white, and being white means that the solar radiation that comes down and strikes it largely gets reflected away and goes back to space.

Sea ice helps cool our planet by reflecting sunlight back to space and also by trapping heat in the ocean, where the heat can’t escape as quickly to the atmosphere. Dr. Parkinson spoke of the loss of sea ice cover in the Arctic.

We can see a clear long-term trend, which is a trend toward lesser sea ice coverage. And it turns out that it’s overall about 3 to 4% per decade reduced sea ice coverage since the late 1970s.

That means that, every year since the 1970s, we’ve lost an area of Arctic sea ice about the size of Switzerland. Many scientists now suggest we’ll see an ice-free Arctic in the summertime in this century – although some ice will still return each winter. An ice-free Arctic would open shipping lanes at the top of our planet. On the negative side…

The reduced ice cover would remove this reflective white cover over the Arctic Ocean, and it would mean therefore that the sun’s radiation would be coming in to the Arctic region instead of getting reflected away.

… and that would mean further warming of Earth. What’s more, an ice-free Arctic would affect creatures – such as polar bears and walruses – that live on sea ice. Dr. Parkinson said that sea ice cover grows and shrinks with the seasons. The floating Arctic sea ice to the north is at maximum in winter, when it covers an area about one and a half times the size of Canada. Dr. Parkinson explained more of how NASA’s Aqua satellite measures Earth’s sea ice. She said:

The Aqua Satellite has a key instrument that allows us to see sea ice everyday and get a polar coverage for both the Arctic and the Antarctic. That instrument is the Advanced Microwave Scanning Radiometer for the Earth’s observing systems. The abbreviation is AMSR. It’s an instrument that was provided to NASA’s Aqua Satellite by the Japanese. We have lots of International partners in our various satellite collaborations.

Parkinson explained that the AMSR measures microwave radiation.

There are some real pluses for measuring microwave radiation when we’re looking at the sea ice. And a key one is that sea ice emits a lot more of certain wavelengths of microwave radiation than water does. Therefore, when we get the data from the instrument on how much radiation it’s receiving we can readily tell whether there was sea ice in that little grid element below the satellite, which we call pixel. And not only can you tell whether it had sea ice or not, but because of the contrast between how much microwave radiation is coming out from the sea versus the water, we can actually calculate what percentage of that pixel area is sea ice. And we call that percentage the ice concentration.

Dr. Parkinson said that Aqua is on an extended mission in 2010, on year eight of its planned six-year mission.

Aqua was launched back in May of 2002 and fortunately our record of sea ice goes back well before that, in fact it goes back to the late 1970’s. Prior to satellites you just couldn’t get a good large scale record of the global sea ice coverage.

But since the late 1970’s we’ve had instruments measuring in microwave radiation almost continuously since that time. There are some data gaps. The key launch in the late 1970’s was the NIMBUS-7 satellite, which was a NASA satellite launched in October of 1978. That had a microwave instrument on board that worked really well until 1987. And then the Defense Department launched a microwave instrument. They’ve launched a sequence of microwave instruments that cover the period since 1987. The combination of the NIMBUS-7 measurements and the Defense Department measurements and now the Aqua measurements gave us a really solid record of sea ice distributions and expense since the late 1970’s.

Our thanks today to NASA’s Aqua Mission, improving our knowledge of our home planet through satellite observations.

July 11, 2011

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