It is modern myth that CO2 is melting the Arctic sea ice. No doubt many people will take immediate offence at the mere title of this post but they would do well to listen to the data before they jump. CO2 is supposed to heat the earth's atmosphere and then would melt the ice from above. The atmosphere can't get past the ice to warm the water below so the only logical conclusion is that a warm atmosphere should melt the ice from above.
But what is happening is the Arctic ice is melting from below due to warm waters that normally are about 100-200 m below the surface. I am going to show that due to a change in the winds, the Arctic ocean became more salty (salinization). The increase in salinity caused the underlying deeper waters to come into contact with the ice above, which melts the Arctic ice from below. Unless one can demonstrate that the wind change is due to global warming, one can't claim that CO2 is melting the Arctic ic.
Let's start by looking at the vertical temperature profile of the Arctic ocean. The surface layer, the layer in which the ice floats, is in general is fresher than the warm Atlantic sea water below.
Note that about 200 meters beneath the sea surface, the water temperature is 2 deg C--well above the melting point. If that heat can get up to the surficial layer, past the fresh water, it would melt the ice. Since fresh water is less dense than salt water, the density difference is what keeps the warm water from the ice.
Now, the halocline, the layer of fresh water is about 50-100 meters thick. The ice above is only about 3 meters thick--people think the Arctic sea ice is hundreds of feet thick but it isn't (http://www.arctic.noaa.gov/essay.wadhams.html). What happened in the Arctic is that the halocline, the freshwater layer has been destroyed, or significantly reduced, and that has allowed heat from below to rise beneath the ice, melting it.
Here is how this happened. Below is a comparison of the wind patterns in the 70s and 80s vs, the late 80s and 90s.
The left picture is 1979-1988; the right is 1989-1997. The big high pressure cell (red) present in the earlier times is gone in the later times. And that has had a big impact on the freshwater flow in the surficial waters of the Arctic ocean.
"This study was motivated by observations of significant salinification of the upper Eurasian Basin that began around 1989. Observational data and modelling results provide evidence that increased arctic atmospheric cyclonicity in the 1990s resulted in a dramatic increase in the salinity in the Laptev Sea and Eurasian Basin. Two mechanisms account for the Laptev Sea salinization: eastward diversion of Russian rivers, and increased brine formation due to enhanced ice production in numerous leads in the Laptev Sea ice cover. These two mechanisms are approximately the same intensity and are linked to changes in wind patterns. The resulting Laptev Sea salinity anomaly was then advected to the central Eurasian Basin. The strong salinization over the Eurasian Basin altered the formation of cold halocline waters, weakened vertical stratification, and released heat from the cold halocline layer upward. Our analysis suggests that local processes in the Laptev Sea may have a dramatic basin-wide impact on the thermohaline structure and circulation of the Arctic Ocean." Johnson, M. A., and I. V. Polyakov, The Laptev Sea as a source for recent Arctic Ocean salinity changes, Geophys. Res. Lett., 28, 2017-2020, 2001
The impact of that increased salinization is that the ice is no longer protected from the warmer waters below. Johnson and Polyakov state:
"The replacement of fresh surface waters with more saline waters reduced vertical stratification and increased heat flux, releasing heat from cold halocline layer to upper layers of the Eurasian Basin. The corresponding heat flux increase for the 1989-1997 period is as much as 3 W/ m-2 (Figure 4B) in this region, comparable to the change in heat flux over the Lomonosov Ridge and Amundsen Basin computed from SCICEX'95 data and a 1-D mixing model [Steele and Boyd, 1998]." Johnson, M. A., and I. V. Polyakov, The Laptev Sea as a source for recent Arctic Ocean salinity changes, Geophys. Res. Lett., 28, 2017-2020, 2001
Swift et al, say the same thing--that the heat from below is warming the ice above, melting it.
"The halocline is the principal density structure of the Arctic Ocean, separating the cold surface mixed layer from the warm Atlantic layer that lies below about 200 m. The climatic importance of the halocline is well recognized [e.g., Aagaard et al., 1981]. Some observations have suggested that regionally the halocline has thinned dramatically during the past 10-15 years, possibly sufficiently to increase the upward heat flux to the sea surface and its ice cover [Steele and Boyd, 1998]. Other recent work has linked large and rapid changes in the properties of halocline waters to shelf processes, including the melting of sea ice on the Barents shelf [Woodgate et al., 2001] and increased freezing in the Laptev Sea [Johnson and Polyakov, 2001]. There is in any event ample justification to seek evidence of earlier halocline changes similar to those during the 1990s." Swift, J. H., K. Aagaard, L. Timokhov, and E. G. Nikiforov (2005), Long-term variability of Arctic Ocean waters: Evidence from a reanalysis of the EWG data set, J. Geophys. Res., 110, C03012 ftp://odf.ucsd.edu/pub/jswift/2004JC002312.pdf p.8,9
Swift et al looked at records of temperature over the past 50 years looking for previous warming periods. They show a very interesting plot which shows the temperature structure of the Arctic Ocean over time. This picture is from the Nansen Basin.
You can see that there were warm periods in the underlying water three times during the past, the early 1950s, the mid 1960s and the early 1970s.
What is happening in the Arctic is not unprecedented. Shoot, 5000 years ago, all the permafrost around the arctic was melted.
" We find that beginning about 1976, most of the upper Arctic Ocean became significantly saltier, possibly related to thinning of the arctic ice cover. There are also indications that a more local upper ocean salinity increase in the Eurasian Basin about 1989 may not have originated on the shelf, as had been suggested earlier. In addition to the now well-established warming of the Atlantic layer during the early 1990s, there was a similar cyclonically propagating warm event during the 1950s. More remarkable, however, was a pervasive Atlantic layer warming throughout most of the Arctic Ocean from 1964–1969, possibly related to reduced vertical heat loss associated with increased upper ocean stratification. A cold period prevailed during most of the 1970s and 1980s, with several very cold events appearing to originate near the Kara and Laptev shelves. Finally, we find that the silicate maximum in the central Arctic Ocean halocline eroded abruptly in the mid-1980s, demonstrating that the redistribution of Pacific waters and the warming of the Atlantic layer reported from other observations during the 1990s were distinct events separated in time by perhaps 5 years. We have made the entire data set publicly available." Swift, J. H., K. Aagaard, L. Timokhov, and E. G. Nikiforov (2005), Long-term variability of Arctic Ocean waters: Evidence from a reanalysis of the EWG data set, J. Geophys. Res., 110, C03012
Now as long ago as 1998 it has been known that the warm waters beneath the ice was in direct contact with the ice, yet the global warming hysteriacs continue to ignore the scientific data
" Changes are also seen in other halocline types and in the Atlantic Water layer heat content and depth. Since the cold halocline layer insulates the surface layer (and thus the overlying sea ice) from the heat contained in the Atlantic Water layer, this should have profound effects on the surface energy and mass balance of sea ice in this region. Using a simple mixing model, we calculate maximum ice-ocean heat fluxes of 1–3 W m−2 in the Eurasian Basin, where during SCICEX'95 the surface layer lay in direct contact with the underlying Atlantic Water layer." Steele, M., and T. Boyd (1998), Retreat of the cold halocline layer in the Arctic Ocean, J. Geophys. Res., 103(C5), 10,419–10,435
Remember that the warm underlying Atlantic water is in direct contact with the ice above and that this is due to the salinization of the Arctic water. Here is the history of the salinization of the Arctic.
Clearly about the time that the Arctic ice began to melt, the sea became more salty. CO2 is not melting the ice; the underlying warm water coming into contact with the ice from beneath is what is melting the Arctic ice.
Why do the global warming hysteriacs NEVER, EVER tell you this? Is it because they simply are pushing a political agenda rather than real science?