By Steve Goddard
Yesterday, WUWT reported on a University of Melbourne study claiming that melting ice is behind the warming of the Arctic.
“Findings published in Nature today reveal the rapid melting of sea ice has dramatically increased the levels of warming in the region in the last two decades. The sea ice acts like a shiny lid on the Arctic Ocean. When it is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it.”
If this were true, we would expect to see that months with the most ice loss would also show the most warming. In fact, we see the exact opposite. As you can see in the graph below, most Arctic warming from 1979-present has occurred in the winter and spring, with very little warming during the summer.
By contrast, ice extent trends over that same time interval show that ice loss has occurred mainly during the summer. It appears that the relationship between warming and ice loss is inconsistent with the claims in the University of Melbourne study. Temperatures have increased the least during times of year when ice loss was the greatest.
April is the month which has warmed the most, a full seven months after September - the month of peak ice loss. There is very little variation in ice extent year over year during April – except for this year which is running well above any other recent years.
A couple of other familiar graphs showing the same issues can be seen below. Note in the DMI graph below that Arctic temperatures have not warmed at all during the summer in the central Arctic.
In the Cryosphere Today graph below, you can see that most ice loss has been during the summer, when there has been little or no temperature gain.
The scatter plot below shows Arctic temperature trends vs. the absolute value of ice extent trends, for all 12 months. Note that there is no meaningful correlation between temperature trends and ice loss. In fact, the months with the most increase in temperature seem to be the ones with little ice loss.
The article claims
“ Strong winter warming is consistent with the atmospheric response to reduced sea ice cover.”
But this is inconsistent with the fact that there has been very little reduction in winter ice cover. The temperature of water under the winter sea ice is fixed by thermodynamics at -2C down to a depth of tens of metres, and does not vary from one year to the next. Furthermore, the rate of heat transfer through 2-5 meter thick 99+% concentration ice, is very low. NSIDC is currently showing ice extent right at the 1979-2000 mean, and above the 1979-2009 mean – yet temperatures in the Arctic have been well above the mean all through the spring. How is the heat escaping through all the thick, high concentration ice?
The article also claims :
“reduced summer sea ice cover allows for greater warming of the upper ocean….The excess heat stored in the upper ocean is subsequently released to the atmosphere during winter.”
There is a major problem with that theory. The summer minimum occurs at the autumnal equinox when the Arctic is receiving almost no SW radiation, and that which is being received is well below the critical angle of water. By September, the shortage of insulating ice cover is actually causing a net loss of heat from the ocean. NSIDC explains it like this:
“In the past five years, the Arctic has shown a pattern of strong low-level atmospheric warming over the Arctic Ocean in autumn because of heat loss from the ocean back to the atmosphere. …. As larger expanses of open water are left at the end of each melt season, the ocean will continue to hand off heat to the atmosphere.”
In other words, loss of summer ice should produce atmospheric warming in the autumn, but not in the winter and spring when ice is cover is normal or near normal.
Two years ago, WUWT published this article after review by Walt Meier at NSIDC, Roger Pielke Sr. at CU, and Ben Herman at the University of Arizona. It explains why changes in ice cover probably are causing a net cooling effect. None of the reviewers had any substantive disagreements with the conclusions.
Conclusion: The University of Melbourne study claims are not supported by the available data. The authors seem to have jumped right into statistical analysis without proposing a physical mechanism that works. Heat flows across differences in temperatures, yet the winter water temperature under the ice is fixed at -2C. Thus elevated winter air temperatures should actually cause a reduction in heat flow out of the ocean. Whatever is driving increases in winter Arctic temperatures is not heat coming out of the Arctic Ocean, which is covered with insulating ice.
A more logical conclusion would be that the decline in ice thickness is associated with warmer winter temperatures.
If scientific reasoning were limited to the logical processes of arithmetic, we should not get very far in our understanding of the physical world. One might as well attempt to grasp the game of poker entirely by the use of the mathematics of probability.
- Vannevar Bush