Matters arising from D'Aleo 1: Opening comments.

Recently Joseph D'Aleo has posted a reply to Tamino's posts Cold Cherries from Joe D'Aleo and More Cherry Ice from Joe D'Aleo. D'Aleo's response is here.




Firstly D'Aleo cites this NASA page as supporting the claim that "normal, decade-long changes in Arctic Ocean currents driven by a circulation known as the Arctic Oscillation was largely responsible for the major Arctic climate shifts observed over the past several years."

However the page refers to research looking at ocean changes and linking them to the end of the positive index Arctic Oscillation(AO) that persisted during the early 1990s (not the last several years) and is connected with the loss of sea-ice, mainly due to export through the Fram Strait. This is not news in the arena of Arctic science. Indeed in 2001 Torgny Vinje studied export of sea ice through the Fram strait and concluded:

The significant increase of ~40% in the ice efflux from 1990 to 1997 indicates a contemporary decreasing ice thickness in the Arctic Ocean during the recent decade. However, provided a continuation of the observed cycling in the ice efflux, or the atmospheric circulation, we should expect a reduction in the ice efflux, and, a thickening of the ice in the Arctic Ocean during the next decade. A future thickening of the ice is also predicted by Polyakov et al. (1999) in connection with an observed reversal to an anticyclonic ice circulation in the reservoir toward the end of 1990.

This recovery suggested by concentration on natural impacts on the Arctic did not arise, because as we now know the loss of the Arctic sea-ice is clearly and largely due to human activity. Yes, there was a substantial loss of ice in the 1990s, probably due to a natural factor (changes in the AO may be related to stratospheric cooling due to increased greenhouse gasses and CFCs). But we are now more than 15 years on, ample time for plenty of old ice to form. The fact is, it has not, the sea-ice is not recovering.

D'Aleo also cites a 2007 study by Francis in GRL that shows "how the warming in the arctic and the melting ice was related to warm water (+3C) in the Barents Sea moving slowly into the Siberian arctic and melting the ice." I can only presume this to be Francis & Hunter, published in GRL, 2007. That study does find that the PDO may have played a role in recession of the winter sea-ice edge between 1995 and 2005, due to it's influence on winds in the Bering Sea. Although it should be noted that the Arctic Dipole has a substantial recent role in increases of ocean heat flux through the Bering Straits see here. And it is now being seen not as just variation in weather but as a positive feedback on the loss of sea ice, more here

That noted, crucially Francis & Hunter state:

The strong influence of SSTs on winter ice is consistent
with the direct connection between the Barents Sea and the
N. Atlantic and Norwegian Currents [e.g., Mork, 1981]. Sea
surface temperatures in this region have increased substantially
during winter in recent decades [e.g., Comiso, 2006b],
which supports the SST influence identified in this investigation.
The warming in the Barents Sea and adjoining
waters is consistent with modeling studies linking increased
concentrations of greenhouse gases with a warmer N.
Atlantic Ocean [e.g., Hoerling et al., 2001].

My emboldening.

So yes, the PDO may well have had a role in affecting wind changes that influence the winter sea-ice edge, however the overall warming of the waters is consistent with Global Warming driven warming of the Atlantic waters. Furthermore in that paper Francis & Hunter refer to an earlier (2006) paper they published. That paper, Francis & Hunter 2006, finds:

In addition to warming and increased
clouds, more abundant liquid-water-containing
clouds [Zuidema et al., 2005] and increased
atmospheric water vapor content [Wang and
Key, 2005] also appear to be influential.
Trends in satellite-derived observations
(Table 1) likely are caused by a combination
of increased moisture transport from lower
latitudes [Groves and Francis, 2002], as well
as by evaporation from additional ice-free
areas and from an earlier start to the melt
season [Belchansky et al., 2003]. These
changes constitute a positive feedback to
Arctic warming, augmenting the much anticipated
ice-albedo feedback...

...Increased temperatures,
cloud amount, and water vapor—consistent
with global-scale anthropogenic
effects—enhance the atmosphere’s infrared
emission, which reduces the thickness as
well as the extent of the thinner ice cover. As
greenhouse gases continue to increase,
it is plausible, perhaps likely, that this trajectory
will continue.

They also note that in spite of continued losses of ice, there has been a reduced sensitivity of sea-ice to the AO after 1995, this implies that a new player is at work in summer sea-ice extent, this they propose is the substantial increase in downwelling infra-red radiation. As I've discussed before, there are other players, not least of which is the Arctic Dipole Anomaly, see here.


What's currently going on in the Arctic is a complex interplay of various factors. Given that this is the case, is it helpful to get lost in the detail of what individual weather stations show? No. Producing long tracts of graphs of temperature at individual locations serves nothing other than to muddy the waters and obscure the issue at hand. The beauty of even a simple process like averaging is that it brings to the fore the factors that are common to all the data being averaged. And as Hansen and Lebedeff show, even where data sets are not continuous during the periods they run for they can still provide valuable data about widespread signals in the noise of the individual data series.

Hansen and Lebedeff found that between pairs of stations the correlation of annual mean temperature variation decreased with reduced distance between station pairs. They found that whilst very close stations had a correlation of virtually 1, as the stations chosen were further apart the correlation fell, reaching 0.5 at an average of 1200km seperation. Hence they chose to use 1200km as the distance to use in the calculation of temperature anomalies for the GISS global temperature index. Hansen and Lebebeff's figure 3 shows that this correlation behaviour holds for stations from 64.2 to 90 degN latitude.

The importance of this finding is that to see the climatic wood for the regional trees, rather than concentrating on individual locations (which are affected by local and subregional processes, it's important to use the proper mathematical treatment to extract the meaningful patterns. Averaging across the region, or using a technique to allocate temperatures to grid-boxes. By doing that one can get at what is happening across the Arctic.

Bengston 2004, figure 1. Annual mean Arctic surface air temperature anomalies, 5 year running mean.

Given the current warming trend in the Arctic, even if we are to accept that the 1940s were marginally warmer across the Arctic basin. It won't be many years before the Arctic warms well beyond the 1940s warm period. Using a rhetorical tactic with a short fuse on it is not indicative of foresight. But when it comes to the denialist fringe, foresight does not appear to be their strong point.

Part 2.
Part 3.


Francis & Hunter, 2006, "New insight into the disappearing Arctic sea ice."
http://marine.rutgers.edu/~francis/pres/Eos_11-14-2006EO460001.pdf

Francis & Hunter, 2007, "Drivers of declining sea ice in the Arctic winter: A tale of two seas."
http://marine.rutgers.edu/~francis/pres/2007GL030995_winter_ice.pdf

Hansen & Lebedeff, 1987, "Global Trends of Measured Surface Air Temperature."
http://pubs.giss.nasa.gov/docs/1987/1987_Hansen_Lebedeff.pdf

Vinje, 2001, "Fram Strait Ice Fluxes and Atmospheric Circulation: 1950–2000."