The Arctic’s oldest sea ice is disappearing fastest
The Arctic sea ice cap is losing older, thicker sea ice faster than newer, thinner sea ice, according to research from NASA.
Dr Joey Cosimo, a senior research scientist at NASA, assessed Arctic sea ice coverage between 1979 and 2012 using satellite data. The results were published in the Journal of Climate earlier this month.
Cosimo categorised the ice into ‘seasonal ice’ which is newly formed each winter, ‘perennial ice’, which has lasted for at least one summer, and ‘multi-year ice’, which has persisted through at least two summers. The younger, seasonal ice is thinner, saltier and found around the edges of the ice cap.
It turns out that the extent of perennial ice has declined by around 15 per cent per decade. It can be difficult to get a meaningful idea of how these sorts of number actually equate to reality, but comparing the images below clearly shows just how dramatic the decline over the last three decades has been:
Source: NASA. Acquired November 1, 2011 – January 31, 2012
Source: NASA. Acquired November 1, 1979 – January 31, 1980
Cosimo also found that the thickest multi-year ice is actually disappearing faster still, declining by about 17 per cent per decade – a rate of decline which is accelerating.
This has made the ice cap thinner overall, as he explains:
“The average thickness of the Arctic sea ice cover is declining because it is rapidly losing its thick component, the multi-year ice. At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season. It would take a persistent cold spell for most multi-year sea ice and other ice types to grow thick enough in the winter to survive the summer melt season and reverse the trend.”
This video from NASA shows the loss of multi-year ice since 1979:
Overall, the extent of all Arctic sea ice decreased by around 12 per cent per decade over the last three decades, in line with the rise in global temperature over the same period. As Dr Cosimo writes in his paper, Arctic temperature is rising at around three times the average for the whole globe.
Will the vulnerable multi-year sea ice survive future temperature rise? It seems unlikely, given that scientists suggest Arctic seas could be ice-free during summer in the next few decades.