Alarmists are always claiming the Arctic Sea Ice is the “canary in the coal mine.” Wrong. Arctic ice extent varies a lot for a lot of reasons. Predictions of its disappearing because of rising CO2 are another attempt to use a natural process as proof that global warming is dangerous and linked to fossil fuel emissions.
The Long View of NH Sea Ice
First some historical context for how NH ice extent varies over decades and centuries.
Figure 16-3: Time series of April sea-ice extent in Nordic Sea (1864-1998) given by 2-year running mean and second-order polynomial curves. Top: Nordic Sea; middle: eastern area; bottom: western area (after Vinje, 2000). IPCC Third Assessment Report
“The extent of ice in the Nordic Seas measured in April has been subject to a reduction of ~33% over the past 135 yr. Nearly half of this reduction is observed over the period ~1860–1900, prior to the warming of the Arctic. Decadal variations with an average period of 12–14 yr are observed for the whole period. The observation series indicates that less than 3% of the variance with respect to time can be explained for a series shorter than 30 yr, less than 18% for a series shorter than 90 yr, and less than 42% for the whole 135-yr long series. While the mean annual reduction of the April ice extent is decelerating by a factor of 3 between 1880 and 1980, the mean annual reduction of the August ice extent is proceeding linearly.”
“The August ice extent in the Eastern area has been more than halved over the past 80 yr. A similar meltback has not been observed since the temperature optimum during the eighteenth century. This retrospective comparison indicates accordingly that the recent reduction of the ice extent in the Eastern area is still within the variation range observed over the past 300 yr.”
Anomalies and Trends of Sea-Ice Extent and Atmospheric Circulation in the Nordic Seas during the Period 1864–1998 by TORGNY VINJE, Norwegian Polar Institute, Oslo, Norway
Multiple Factors Affecting Sea Ice Extent
The references below, among many others, show that the factors causing Arctic Ice to lessen, when that was happening, have nothing to do with air temperatures which is the only way CO2 could have an effect (theoretically). The melting is much more the result of water circulations, especially when warm Atlantic water from the south is able, or not, to get into the Arctic Ocean.
“Regional Arctic sea ice variations result from atmospheric circulation changes and in particular from ENSO and North Atlantic Oscillation (NAO) events. Patterns of Arctic surface air temperature changes and trends are consistent with regional changes in sea ice extent. A dominant mode of Arctic variability is the Arctic Oscillation (AO), and its strong positive phase during the 1990s may account for much of the recent decrease in Arctic ice extent. The AO explains more than half of the surface air temperature trends over much of the Arctic.”
“The variation in the ice extent caused by a 1C change in the ocean temperature since 1860 compares with about 90% of the concurrent total ice extent variation observed in the eastern area. The net effect of atmospheric temperatures seems accordingly to be relatively small over the same period of time. This concurs with the large difference in the individual heat capacity.”
“So why does circulation matter? Two reasons. First off, you can see warm water entering on the Pacific and Atlantic connections and cold water leaving via Canada and Greenland / Fram Strait. During a Glacial, that circulation stops. With a mile of ice over Canada, that exit is closed. With ocean levels 100 meters lower, folks can walk from Russia to Alaska. (Well, they do it sometimes now over the ice, but it will be easier and less seasonal during a Glacial).”
“So look again. No Bering Sea warm intrusion. No Canadian cold drain. No Beaufort Gyre when the ice is deep, since there will be no wind driven circulation under the ice. The Asian current toward the Bering Sea will end. The entire Asian warm river drain into the Arctic likely freezes up and doesn’t happen – which raises the interesting question of where does it go then? But that is for another day. Like asking where the Alaskan rivers drain then, or are they just glaciers at that point?”
“In short, what is left is just the North Atlantic Drift (aka Gulf Stream for Americans) warming a small patch near Europe and some cold water near Greenland. As Scotland was under ice in the last Glacial, even that North Atlantic Drift circulation likely didn’t get very far north.”
In addition to water circulation effects, sea ice extent is influenced by clouds and winds.
“Researchers have found that the high amounts of cloud in the early summer lead to low concentrations of sea ice in the late summer. This relationship between cloud cover and sea ice is so strong that it can explain up to 80 per cent of the variation in sea ice over as much as 60 per cent of the the sea ice area.”
“We have shown evidence that low level winds over the Arctic, play an important role in mediating the rate of retreat of sea ice during summer. Anomalous anticyclonic flow over the interior of the Arctic directed toward the Fram Strait favors rapid retreat and vice versa. We have argued that the relative rankings of the September SIE for the years 2007, 2010 and 2011 are largely attributable to the differing rates of decrease of SIE during these summers, which are a consequence of year-to-year differences in the seasonal evolution of summertime winds over the Arctic. . . It is not clear why anticyclonic wind anomalies have been prevalent in recent years. ”
Like most things in the climate, Arctic sea ice extent is determined by many interacting factors. Among those many influences, the weakest case is claiming CO2 as a driving force.