Arctic Ice Dynamics Destabilizing
Global warming has broken down the relationship between Arctic climate patterns and fluctuations in the volume of Arctic ice.
The thickness and volume of the Arctic icecap vary not only from month to month, but also from decade to decade. This is a normal phenomenon that's driven by cycling atmospheric pressure phases of the Arctic Oscillation (AO). But since the mid 1990s, the waning and gaining of sea ice has no longer been determined entirely by the AO.
Not only does climate influence the thickness of Arctic ice, but ice depth itself affects global climate, even more so than the extent of ice cover. Ice thickness moderates the exchange of energy and transfer of heat between the ocean and atmosphere.
The importance of ice thickness for global climate change prompted researchers from Russia and United States to collaborate on determining how thick perennial Arctic ice was in each month from 1982 to 2003. They amassed data on the ice pack collected over the years from above by surface drilling and from below with submarine sonar. With that information, the scientists trained their neural network algorithm to calculate averages and trends.
They found that over the 22 years, the ice went through three phases: increasing rapidly in thickness, then rapidly decreasing, then modestly increasing. Average thickness in the month of January increased from year to year by 7.6 centimetres (3 inches) between 1982 and 1988. That was followed by a period, until 1996, where annual losses were 6.1 cm a year. After that, ice thickness gained 2.1 cm annually.
Those phases were driven by the regional climate pattern generated by the Atlantic Oscillation. When the AO index was low in the 1980s, high-pressure weather prevailed over the Arctic, keeping air temperatures cold. The shift to a high AO phase produced longer melting seasons which accelerated the shedding of old ice and thinned the ice pack. Since the mid 1990s, the AO index has been fairly neutral, enabling ice to slowly thicken.
The total volume of ice located north of 65 degrees latitude tracked the trends in ice thickness, up until 1996. The Arctic sea ice gained 2500 cubic kilometres (600 cubic miles) in the 1980s, then lost 4000 km³ until 1996 as ice thinned under the high-index AO.
But since then, although the ice has thickened, there has been no corresponding gain in volume. The extraordinary retreat in extent of late summer sea ice over the Arctic region recently has been compensated for by the AO being in a phase that's allowing ice near the pole to grow thicker. This balance is not expected to last.
G.I. Belchansky, D.C. Douglas and N.G. Platonov. 2008. Fluctuating Arctic Sea Ice Thickness Changes Estimated by an In Situ Learned and Empirically Forced Neural Network Model. Journal of Climate. 21(4): 716-729.