By Steve Goddard and Anthony Watts
The Navy requires accurate sea ice information for their operations, and has spent a lot of effort over the years studying, measuring, and operating in Arctic ice both above and below, such as they did in the ICEX 2009 exercise.
So, if you are planning on bringing a $900 million Los Angeles class submarine through the ice, as the captain might say to the analyst after receiving an ice report: “you’d better be damn sure of the ice thickness before I risk the boat and the crew”.
Below is a blink comparator of U.S. Navy PIPS sea ice forecast data, zoomed to show the primary Arctic ice zone.
The blink map above shows the change in ice thickness from May 27, 2008 to May 27, 2010. As you can see, there has been a large increase in the area of ice more than two metres thick – turquoise, green, yellow and red. Much of the thin (blue and purple) ice has been replaced by thicker ice.
Source images for the blink comparator:
This was quantified by measuring the area percentage in the Arctic Basin of the 0-1, 1-2, 2-3, 3-4, and 4-5 metre ranges. The graph below shows the results. This technique assumes an equal area projection, which should be fairly accurate north of 70N.
In 2008, less than half of the ice (47%) was greater than two metres thick. Now, more than 75% of the ice is greater than two metres thick. In 2008, 18% of the ice was more than three metres thick. This year that number has increased to 28%. There has been nearly across the board ice thickening since 2008. There was slightly more 4-5 metre ice in 2008, due to the big crunch in the summer of 2007.
Now on to calculating the volume. That calculation is straightforward :
volume = (A1 * 0.5) + (A2 * 1.5) + (A3 * 2.5) + (A4 * 3.5) + (A5 * 4.5)
Where A1 is the area of ice less than one metre, A2 is the area of ice less than two metres, etc. The 2010/2008 volume ratio came out to 1.24, which means there has been approximately a 25% increase in volume over the last two years. The average thickness has increased from about 2.0 metres to 2.5 metres. That means an extra 20 inches of ice will have to melt this summer. So far, this seems unlikely with the cold Arctic temperatures over the last couple of weeks.
Now let’s look at the volume percentages. In 2010, 87% of the ice (by volume) is greater than two metres thick. But in 2008, only 64% of the ice (by volume) was greater than two metres thick.
A few weeks ago, when extent was highest in the JAXA record, our friends were asking for “volume, not extent.” Their wishes have been answered. Ice volume has increased by 25% in the last two years, and those looking for a big melt are likely going to be disappointed.
Here is the measured data:
Do you think it odd that this increase isn’t prominently mentioned on the PIOMAS site? It seems very relevant.
If a man will begin with certainties, he shall end in doubts; but if he will be content to begin with doubts he shall end in certainties.
– Sir Francis Bacon
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