Over at NASA, they have a press release about old Arctic sea ice disappearing since 1980, including a helpful comparison widget that splits the before and after for comparison. I’ll run it in full below followed by comments.
NASA Finds Thickest Parts of Arctic Ice Cap Melting Faster
GREENBELT, Md. — A new NASA study revealed that the oldest and thickest Arctic sea ice is disappearing at a faster rate than the younger and thinner ice at the edges of the Arctic Ocean’s floating ice cap.
The thicker ice, known as multi-year ice, survives through the cyclical summer melt season, when young ice that has formed over winter just as quickly melts again. The rapid disappearance of older ice makes Arctic sea ice even more vulnerable to further decline in the summer, said Joey Comiso, senior scientist at NASA Goddard Space Flight Center, Greenbelt, Md., and author of the study, which was recently published in Journal of Climate.
The new research takes a closer look at how multi-year ice, ice that has made it through at least two summers, has diminished with each passing winter over the last three decades. Multi-year ice “extent” – which includes all areas of the Arctic Ocean where multi-year ice covers at least 15 percent of the ocean surface – is diminishing at a rate of -15.1 percent per decade, the study found.
There’s another measurement that allows researchers to analyze how the ice cap evolves: multi-year ice “area,” which discards areas of open water among ice floes and focuses exclusively on the regions of the Arctic Ocean that are completely covered by multi-year ice. Sea ice area is always smaller than sea ice extent, and it gives scientists the information needed to estimate the total volume of ice in the Arctic Ocean. Comiso found that multi-year ice area is shrinking even faster than multi-year ice extent, by -17.2 percent per decade.
“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,” Comiso said. “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.”
Scientists differentiate multi-year ice from both seasonal ice, which comes and goes each year, and “perennial” ice, defined as all ice that has survived at least one summer. In other words: all multi-year ice is perennial ice, but not all perennial ice is multi-year ice (it can also be second-year ice).
Comiso found that perennial ice extent is shrinking at a rate of -12.2 percent per decade, while its area is declining at a rate of -13.5 percent per decade. These numbers indicate that the thickest ice, multiyear-ice, is declining faster than the other perennial ice that surrounds it.
As perennial ice retreated in the last three decades, it opened up new areas of the Arctic Ocean that could then be covered by seasonal ice in the winter. A larger volume of younger ice meant that a larger portion of it made it through the summer and was available to form second-year ice. This is likely the reason why the perennial ice cover, which includes second year ice, is not declining as rapidly as the multiyear ice cover, Comiso said.
One of the most often complained about things from icy fanatical folks like Tamino (aka Grant Foster) and Neven Acropolis on their blogs is “cherry picking”.
Generally, cherry picking claims are applied when you pick a section out of datasets, and use that short section to draw a conclusion. For example, over at Steve Goddard’s blog he has nice multi-year sea ice plot from NSIDC where he’s suggesting the short term gain in 2 and 3 year old multi-year ice is significant against the larger down trend.
The ongoing loss of 4 and 5 year old ice would tend to confirm the premise of the NASA article.
But I want to expand the scope a bit. For the first time in history, starting about 1980 with the advent of satellite remote sensing, we have geophysical data we’ve never had before. The trouble is, that 30+ year period from 1980-2012 is just barely over a 30 year climate normals period. We don’t know what sea ice extent and age trends were before that, as there really aren’t any good data on the Arctic ice pack prior to 1980.
For example if you visit the Wikipedia page Polar Ice Packs, you won’t find anything about historical sea ice data prior to that, but plenty about recent declines. They do though have a century scale model from 1950 to 2050 that posits a loss of thickness.
I’m not sure where they got that high resolution data for 1955, since we didn’t have any satellites then (Sputnik launched in 1957 and had no remote sensing capability, only a radio beacon beeper so you could track it) and we didn’t have under the ice submarines (to measure ice thickness) then either as the USS Nautilus (SSN-571) was the first vessel to complete a submerged transit beneath the North Pole on August 3, 1958.
Even the USS Skate (SSN-578) didn’t surface at the North Pole through the ice until 1959. Here’s that photo again that drives Tamino and Neven crazy when they see it because it shows open water in the Arctic in 1958:
From John Daly: (added)
For example, one crew member aboard the USS Skate which surfaced at the North Pole in 1959 and numerous other locations during Arctic cruises in 1958 and 1959 said:
“the Skate found open water both in the summer and following winter. We surfaced near the North Pole in the winter through thin ice less than 2 feet thick. The ice moves from Alaska to Iceland and the wind and tides causes open water as the ice breaks up. The Ice at the polar ice cap is an average of 6-8 feet thick, but with the wind and tides the ice will crack and open into large polynyas (areas of open water), these areas will refreeze over with thin ice. We had sonar equipment that would find these open or thin areas to come up through, thus limiting any damage to the submarine. The ice would also close in and cover these areas crushing together making large ice ridges both above and below the water. We came up through a very large opening in 1958 that was 1/2 mile long and 200 yards wide. The wind came up and closed the opening within 2 hours. On both trips we were able to find open water. We were not able to surface through ice thicker than 3 feet.”
– Hester, James E., Personal email communication, December 2000
So where does NOAA get 1955 high resolution data on Arctic sea ice thickness? One wonders. Wikipedia cites the source as http://www.gfdl.noaa.gov/visualization-gallery but when you go there, there’s no record of the plot. Even when you go to the page at GFDL for the graphics used in IPCC’s AR4, you don’t find this visualization anywhere, nor do they have any data prior to 1980 to visualize with.
In fact it seems the Wikipedia source page is the only place that 1955-2055 visualization exists anymore. Perhaps it has been deep-sixed at NOAA after somebody pointed out the folly of it like I did with another visualization blunder from the same group.
Back to the main point.
You can plot, model, and visualize all you want, but there’s just no good sea ice thickness nor extent data prior to 1980 when satellite remote sensing came on the scene, yet we do have anecdotal evidence of previous Arctic ice retreats. For example, this now famous report from 1922 that first appeared in the Washington Post.
In fact, so little ice has never before been noted.
But do we have any Arctic wide data for 1922? No. We also don’t have any Arctic wide data for the Little Ice Age (LIA), The Medieval Warm Period (MWP), Dark Ages Cold Period (DACP) and the Roman Warm Period (RWP). We do however have temperature reconstructions from Ljungqvist (2010) like the one below:
These alternating warm/cold periods, in Ljungqvist’s words: (Source CO2 Science)
“probably represent the much discussed quasi-cyclical c. 1470 ± 500-year Bond Cycles (Bond and Lotti, 1995; O’Brien et al., 1995; Bond et al., 1997, 2001; Oppo, 1997),” which “affected both Scandinavia and northwest North America synchronically (Denton and Karlen, 1973)” and have “subsequently also been observed in China (Hong et al., 2009a,b), the mid-latitude North Pacific (Isono et al., 2009) and in North America (Viau et al., 2006), and have been shown to very likely have affected the whole Northern Hemisphere during the Holocene (Butikofer, 2007; Wanner et al., 2008; Wanner and Butikofer, 2008), or even been global (Mayewski et al., 2004).”
Now it could be argued strongly that since we are in the Current Warm Period (CWP) and Arctic Sea Ice is on the decline, and the rise of the machines in the industrial age coincides with that, that man has the greatest influence on Arctic Sea Ice. That may be, but we just don’t know. We have no good ice data prior to 1980. We do however have suggestions that much of Earth’s climate and responses to it (like Arctic sea ice) is cyclic.
And with only just over 30 years of good sea ice data, how does one determine if this downturn isn’t just part of a regular cycle? For all we know, we may be simply looking at one part of a larger cycle. In fact, a recent peer reviewed paper says “there appear to have been periods of ice free summers in the central Arctic Ocean” in the early Holocene, about 10-11,000 years ago
In that larger context, using 30 years of Arctic sea ice data to draw conclusions and model out to 2050 might very well be viewed as an exercise in cherry picking.
Suggestions by NASA in 2007, in Smedsrud Et Al 2011 and recently in Wang, Song, and Curry suggest that wind patterns are a big factor in the Arctic puzzle. There’s also direct evidence that soot from the industrialization of Asia is collecting in the Arctic and could be a factor in albedo changes in the Arctic which contribute to ice loss.
Sea ice is a complex problem, and my personal view is that we simply don’t know enough about its behavior in the larger context to demonstrate a causal relationship with the recent global temperature increases.
And speaking of global, then there’s that pesky Antarctic, which has an upward trend in sea ice area:
Image from Jeff Condon via his Air Vent blog.
And then of course, unless you believe Steig’s (2009) application of Mannian statistical madness, there’s no evidence that Antarctica has any statistically significant temperature trend. That claim has been disproved by O’Donnell et al 2010.
Global sea ice hasn’t varied all that much in 30 years, and I for one, am just not all that worried about it. Especially since the Great Pacific Climate Shift occurred right about the start of the satellite data, and you all know what our friends tell us about starting conditions.
Image above from this excellent essay on The Air Vent
You can track sea ice in the NH and SH on WUWT’s sea ice page.