By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(Translated/edited with permission by P Gosselin)
Summer is now in full swing and the Arctic sea ice that formed over the wintertime is now steadily melting. Typically the minimum in sea ice extent is reached in mid September. Last year (2012) a new melt record was reached for the satellite era, which however only officially started in 1979. How does it look this year?
The Center for Ocean and Ice of the Danish Ocean Meteorological Service provides a new ice graphic on a daily basis and so that the situation can be monitored. The Arctic sea ice extent of 2013 is depicted by the bold dark line on the chart below (Figure 1). This year there is considerably more ice than there was over the three previous years, which perhaps has something to do with the especially hard winter and the late summer start. It remains to be seen how this will develop further. Also in Alaska and the Baltic Sea larger than normal sea ice areas were observed.
Figure 1: Arctic sea ice extent over the years. Source: DMI.
In the meantime it has been officially confirmed that the north polar ice minimum of 2012 was mostly caused by a powerful storm. Three new studies have been able document this (Simmonds & Rudeva 2012, Parkinson & Comiso 2013 and Zhang et al. 2013). The storm ripped apart the ice cover and scattered the ice to the oceans. Also playing a role was the reduced ice thickness. The high temperatures of the current moderm warm period has helped to reduce the sea ice thickness over time, thus allowing the wind to have an easier time than it did earlier.
How did things look before the satellite age?
Here we find some surprises: Thin, shrinking ice was also common in earlier times, but it was not possible to measure it extensively. One phase of especially low sea ice in the Arctic occurred between 1920 and 1950 when submarines were able to surface in ice-free waters directly at the North Pole. A good overview of this period can be found at Judith Curry’s blog.
Now how does that fit with the notion that sea ice would move only in one direction, namely shrink? Strictly speaking the satellite era of sea ice measurement did not begin in 1979, but already a few years earlier. And if these data are accounted for, then an unexplainable disruption occurs in the curve as shown by (Figure 2). The sea ice coverage of 1973-1975 was significantly less than it was at the “official” start of the dataset: 1979. Interestingly this graphic had been included in the first IPCC climate report, but then it was left out in the subsequent reports because it did not fit with the desired catastrophe narrative.
Figure 2: Arctic sea ice extent 1973-1990. From the IPCC AR1.
Slowly scientists are now finding out how fluctuations in Arctic sea ice could be happening. In a paper published in the International Journal of Climatology a team of scientists were able to show that sea ice extent in the western Arctic ocean is 40-79% controlled by natural ocean cycles. Among these is the Arctic Oscillation (AO). Another team of scientists from MIT generated improved Arctic sea ice prognoses where ocean cycles and the associated patterns play a more important role.
When natural ocean cycles are taken into account, then one needs not wonder when the sea ice season in the Beaufort Sea in the Canadian Arctic lasts considerably longer than it did in the late 19th century and the first half of the 20th century. This is shown in the journal of Biogeosciences where the authors reconstructed sea ice cover over the last 150 years. While sea ice covers the the Beaufort sea an average of 9.4 months per year today, earlier it was only 8.3 months. Back then water in this sea was about 3°C warmer than today. According to this new study the Arctic Oscillation and the Pacific Decadal Oscillation (PDO) played a great role.
The search for other factors effecting Arctic sea ice coverage continues on. There is evidence that the the sun could have a hand in the game. Also changes in measurement methodology and the evaluation routines have caused jumps in the curves. Does a melting Arctic present only disadvantages? It does not make a contribution to sea level rise because there is almost no net water displacement by floating ice that melts. Judith Curry’s blog names a few economic advantages of a low-ice Arctic Ocean.
Finally everyone wants to know how the Arctic sea ice will develop further. A couple of decades ago scientists were predicting an ice-free Arctic already for today. As this prediction failed to materialize, the date was promptly postponed to 2030. In the journal of Geophysical Research Letters, a team of scientists took a closer look and made more comprehensive calculations. Their result: If one assumes even the most aggressive warming prognoses, an ice-free north polar sea summer could be expected only at the end of the 21st century and a year-round ice-free Arctic Ocean at the end of the 23rd century.