Satellite image concentration of sea ice on Canadian Archipelago (right side, purple = thicker ice)
Ice – III
Melting and Moving Ice
2008-08-30The few media reports that filter their way through our limited internet access this far north show that experts are expecting new lows in arctic ice yet again this summer. Traveling with an ice scientist on board the Healy allows us to understand better what we are seeing first-hand as we pass through what is clearly a melting and shifting ice scape. Dr. Pablo Clemente-Colon, originally from Puerto Rico, is the lead scientist at the National Ice Center, which is part of NOAA, the National Oceanic and Atmospheric Administration.
A few statistics from Pablo help set the scene for what we are seeing: a mix of differently aged ice and a disappearance of the thickest, oldest multi-year arctic ice. As more multi-year ice melts each summer, it is harder for it to recover in winter. The thicker, older ice is replaced with younger, thinner ice, which also melts more quickly in the summer. Both kinds of melting open up more water and create more melt pools on what ice remains: both kinds of water are darker than snow and ice. With increasingly less (white) ice to reflect solar energy and increasingly more (dark) water to absorb it, the feedback loop is exacerbated and melting is accelerated, in what is known as the albedo effect.
Slide courtesy of Dr. Pablo Clemente-Colón
Summer is always a melting season for arctic ice, but over the 28 years since 1979, when satellite measurements first began, the drop in summer ice coverage of the Arctic has been considerable. Pablo provided the first two figures below; the NSIDC* provided the last one, showing the following declines in summer ice coverage in the Arctic:
September 1979: 14.16 million km2
September 2007: 3.98 million km2
August 2008*: 3.43 million km2
*From the National Snow and Ice Data Center, which is a separate entity from the NIC.
With some two weeks still to go in the Arctic summer the last figure above is likely to drop even more. And this is despite the fact that the past winter (2008-08) was colder than the year before and allowed the ice to recover some over the winter months.
The preceding information about the extent of ice cover is gathered primarily by satellite. Ice thickness is another important indicator, measured by buoys that are positioned in the ice and drift with it throughout the various arctic seasons. Buoy data over the last twenty years shows a decrease in thickness of the ice (see figure above).
Based on these figures and other observations, ice experts seem to agree that the actual rate of ice decrease is faster than in previous years. There is simply not much 10+ year ice now left. The thickest ice we have seen appears to be more along the lines of 4 to 5 year ice; only when we stopped at the ice island to deploy the buoy did we come close to seeing thicknesses indicating an age of 8 to 10 years old multi-year ice. As Pablo says, the "precipitous decrease in older ice 1988-1990" is simply continuing. Once that older ice disappears, either by melting or by being moved out of the Arctic by wind and ocean currents, it is much harder to keep the overall ice pack intact.
The image below shows the difference between 1987 and 2007 in the amount of multi-year ice (in white). Steve Howard, the high school science teacher who is traveling with us, describes the movement of ice in the arctic as follows. Since I shared his misconception about how ice moves in the Arctic, I pick up his narrative there:
"One major misconception that I had was that the thickest part of the Arctic Ice Cap was centered on the North Pole. I see now that the ice coverage up here is very dynamic, with wind and water currents pushing the floes around the Arctic Ocean basin like flakes in a cereal bowl. Currently, the thickest ice is not centered on the Pole, but closer to the northern coast of Greenland and the Canadian Archipelago. [As Pablo indicates]… . the Arctic sea ice is retreating faster than previous climate change models had predicted, a consequence of an overall warming of the Arctic at twice the global rate in combination with other atmospheric and oceanic processes…. Anomalous weather patterns, perhaps associated with o ther global changes, have helped blow a lot of this ice out of the Arctic Basin and into the Atlantic Ocean, where it drifts southward and eventually melts." To read more of Steve’s chronicles of day-to-day activities and life on board the Healy, visit his blog.
September 1979: 14.16 million km2
September 2007: 3.98 million km2
August 2008*: 3.43 million km2
*From the National Snow and Ice Data Center, which is a separate entity from the NIC.
With some two weeks still to go in the Arctic summer the last figure above is likely to drop even more. And this is despite the fact that the past winter (2008-08) was colder than the year before and allowed the ice to recover some over the winter months.
The preceding information about the extent of ice cover is gathered primarily by satellite. Ice thickness is another important indicator, measured by buoys that are positioned in the ice and drift with it throughout the various arctic seasons. Buoy data over the last twenty years shows a decrease in thickness of the ice (see figure above).
Based on these figures and other observations, ice experts seem to agree that the actual rate of ice decrease is faster than in previous years. There is simply not much 10+ year ice now left. The thickest ice we have seen appears to be more along the lines of 4 to 5 year ice; only when we stopped at the ice island to deploy the buoy did we come close to seeing thicknesses indicating an age of 8 to 10 years old multi-year ice. As Pablo says, the "precipitous decrease in older ice 1988-1990" is simply continuing. Once that older ice disappears, either by melting or by being moved out of the Arctic by wind and ocean currents, it is much harder to keep the overall ice pack intact.
The image below shows the difference between 1987 and 2007 in the amount of multi-year ice (in white). Steve Howard, the high school science teacher who is traveling with us, describes the movement of ice in the arctic as follows. Since I shared his misconception about how ice moves in the Arctic, I pick up his narrative there:
"One major misconception that I had was that the thickest part of the Arctic Ice Cap was centered on the North Pole. I see now that the ice coverage up here is very dynamic, with wind and water currents pushing the floes around the Arctic Ocean basin like flakes in a cereal bowl. Currently, the thickest ice is not centered on the Pole, but closer to the northern coast of Greenland and the Canadian Archipelago. [As Pablo indicates]… . the Arctic sea ice is retreating faster than previous climate change models had predicted, a consequence of an overall warming of the Arctic at twice the global rate in combination with other atmospheric and oceanic processes…. Anomalous weather patterns, perhaps associated with o ther global changes, have helped blow a lot of this ice out of the Arctic Basin and into the Atlantic Ocean, where it drifts southward and eventually melts." To read more of Steve’s chronicles of day-to-day activities and life on board the Healy, visit his blog.
