To support his claim that Arctic sea ice decline is just natural variation, D’Aleo makes this claim:
The temperatures in the arctic have indeed risen in recent years and ice has declined, bottoming out in 2007 but it is not unprecedented nor unexpected. The arctic temperatures and arctic ice extent varies in a very predictable 60-70 year cycle that relates to ocean cycles which are likely driven by solar changes.
Has Arctic sea ice extent really varied “in a very predictable 60-70 year cycle”? One can’t help but wonder, since nowhere in his post does D’Aleo show any graph, or point to any actual data, to support that claim.
Let’s look at some actual data. One of the best long-term (on a century time scale) estimates of Arctic sea ice is the Walsh & Chapman data set (described in Walsh & Chapman 2001, Annals of Glaciology, 33, 444-448). It’s based on a vast array of available information, as described in Walsh & Chapman:
The primary sources of the post-1972 data are the hemispheric fields of sea-ice concentration from (1) the U.S. National Ice Center (NIC), whose weekly grids (derived primarily from satellite data) span the period 1972-1994, and (2) the satellite passive-microwave grids from the Scanning Multichannel Microwave Radiometer (SMMR)/Special Sensor Microwave/Imager (SSM/I) period, 1978-97 (Parkinson and others, 1999). As described by Walsh and Johnson (1979), the primary sources for the period from the early 1950s to the early 1970s were the charts of the U.K. Meteorological Office, the Canadian Atmospheric Environment Service, the U.S. Naval Oceanographic Office, the Danish Meteorological Institute and the Icelandic Glaciological Society. For the first half of the 20th century, a primary source was the monthly April-September chart series of the Danish Meteorolgical Institute, digitized by Kelly (1979), and the corresponding wintertime information digitized by our group using the summaryies of ship reports in the yearbooks of the Danish Meteorological Institute. An additional source of data for the first half of the 20th century is the recent digitization of the Norwegian Polar Institute’s sea-ice charts by T. Vinje and R. Colony (Vinje, 1999). Since the Norwegian digital data also include the more recent decades, we added these data to the eastern North Atlantic portions of our grids through 1972, the year when the hemispheric dataset of the NIC was initiated. We also note that the Norwegian dataset extends well back into the pre-1900 period, permiting even longer temporal extensions for the eastern North Atlantic.
Note that they went out of their way to gather information from as many sources as possible. That’s the way real scientists work.
And what did they find? Here is the annual average for Arctic sea ice from the Walsh & Chapman dataset:
Contrary to what Joe D’Aleo claims, arctic sea ice extent does not vary “in a very predictable 60-70 year cycle” — not even close.
What it does do is show variations throughout the last century and more, but the dramatic decline (due to global warming) doesn’t start until the latter half of the century, about 1960. And the decline has accelerated, becoming far more dramatic, since about the year 2000, leading to annual average sea ice loss of around three million square kilometers. Imagine that.
Of course the data are less certain prior to the satellite era, less certain still prior to 1953, and even more uncertain before 1900. But don’t believe that the Brits, Americans, Canadians, Norwegians, and Danes are all so incompetent that they managed to miss some three million square kilometers of ice. That’s not real skepticism, it’s the kind of wishful thinking that only suits fake skeptics.
Walsh & Chapman actually provide a gridded data set, as well as pan-Arctic averages for all four seasons of the year. Here are the seasonal averages:
Arctic sea ice has declined — dramatically — in all four seasons. But in none of the seasons is there any sign that it varies “in a very predictable 60-70 year cycle” — not even close.
In fact the summertime average has dropped to about half its value throughout most of the 20th century. Imagine that.
Perhaps Joe D’Aleo actually believes in the “very predictable 60-70 year cycle” which isn’t supported by any evidence. Maybe he truly believes that the Brits, Americans, Canadians, Norwegians, and Danes are all so incompetent that prior to the satellite era they managed to see twice as much Arctic sea ice as was really present during the Arctic summer. Who knows, maybe he even believes the fake Arctic regional temperature we discussed previously?