The decline in the Arctic Sea Ice continues. The Arctic Sea Ice minimum in 2011 was (depending on the research group and / or ice characteristic chosen) either the lowest or second lowest on record. While reading this post it is important to remember that the previous lowest Arctic Sea Ice level was in 2007. In fact the 2007 minimum was a complete surprise, being much lower than any one had expected for many years.
Before investigating the detail of this year's minimum here is a video giving an introduction to Arctic Sea Ice.
The second video looks at the 2011 Arctic Sea Ice minimum in more detail.
The video starts with Joe Bastardi. Bastardi continually attempts to argue that there is nothing to worry about with the Arctic Sea Ice. The video shows that his predictions are not even close.
Ice characteristics measured
There are three different ice characteristics that are measured: sea ice extent, sea ice area and sea ice volume
The satellites measure ice in grid cells measuring 25 km by 25 km. For the extent measure if the amount of ice in a cell is over a given threshold (usually 15%) then the whole cell is considered to be 100% ice. Area determines how much actual ice there is. For a more detailed description see this link.
Sea ice volume measures the amount of ice by multiplying the area by the thickness of the ice.
There are five main research groups that report on Arctic sea ice: University of Bremen, IJIS, NSDIC, Piomas and Cryosphere Today.
University of Bremen
According the a research group at the University of Bremen, Arctic Ice Extent had reached "a new historic minimum". See this link for details. The researchers further add:
It seems to be clear that this is a further consequence of the man-made global warming with global consequences.
University of Bremen find the minimum 2011 about 1% lower than that of 2007.
The Cryosphere Today Arctic Sea Ice Area reached a record minimum in 2011. The 2007 minimum value was 2.9194391 million square kilometres and the 2011 value was 2.9047398 million square kilometres. These values can be found at this link. For the 2007 value look at the row starting with 2007.6849 and for the 2011 value row 2011.6931.
Below is a graphical representation of the Cryosphere Today data:
Another method of displaying Arctic Ice Area is by a 365 day rolling average as illustrated below:
Both graphics clearly show the decline since satellite measurements started in 1979. Note also the dramatic declines since 2007.
Imagine two years with the same sea ice extent but year 1 has an average ice depth of 1 metre and year 2 has an average ice depth of 2 metres. Even though extent will measure the two year as identical year 2 will have twice the amount - volume - of ice as year 1. PIOMAS attempts to measure the volume of ice in the Arctic. It uses an ice model but has been carefully validated. See this link for details.
Here is a graph showing the current year (up to the time of writing this post) compared with 2007. It is clear that according to PIOMAS 2011 ice volume has been below that of 2007 for the whole year and reached a new ice minimum this year.
For all of the yearly PIOMAS curves since 2002 see this link.
The chart below shows the PIOMAS ice volume trend since 1980.
In 2011 the NSIDC reported the second lowest ice extent, after 2007.
The minima from 2007 according go NSDIC are:
|Year||Millions of square km|
|1979 to 2010 |
The NSIDC long term trend is like all of the others that I have displayed in this post - the trend is down. See the diagram below:
IJIS also reported the second lowest Arctic sea ice extent for 2011, as shown in the diagram below:
In the previous section I have displayed charts from Cryosphere Today, PIOMAS and NSIDC that clearly show a declining trend in Arctic Sea Ice since satellite measurements began in 1979.
Some people have made the claim that 30 years is too short a period of time to make such a judgement and that the Arctic Sea Ice was also at low levels during the 1930s, therefore there is nothing surprising in the current measurements.
It is possible to determine the levels of Arctic Sea Ice for the era before the direct satellite measurement. Two scientists Walsh and Chapman have developed such a data set. They used reports compiled by MET Offices and Glaciology Institutes in the UK, Canada, Denmark and Norway.
Statistical blogger, Tamino, has used the Walsh and Chapman data to produce the chart below source:
That data shows that the sea ice was quite stable from 1880 to 1960. After 1960 the sea ice level began to decline and that the decline since 2000 has been very dramatic.
Causes of the decline
The University of Bremen group discussed near the beginning of this post stated clearly that the decline in Arctic Sea Ice resulted from man-made global warming.
The GISS temperature anomaly map below shows clearly that the polar regions are warming more rapidly than the rest of the planet. (Most of the polar regions are between 1 degree and 4 degrees warmer than the 1951 to 1980 time period.) Simple intuition indicates that such warming will help to melt ice.
In the second video above, Dr Julienne Stroeve, presents a more detailed argument supporting the view that the decline in Arctic ice is largely the result of global warming:
- the global climate models all show ice decline (though less than is actually occurring)
- if the climate models are run without the carbon dioxide that has been added to the atmosphere (by human activities) then they don't show any ice decline.
Why is the level of Arctic sea ice important?
As the first video demonstrates the Arctic sea ice has:
- an important role in the managing of planetary temperature, less ice means higher temperatures globally
- an important role in maintaining global ocean currents, which have important influences on climate all over the planet.
What about Antarctica and global sea ice?
Antarctic sea ice has increased by 1% per decade during the satellite era. The causes of this are debated amongst scientists. If you look at the temperature anomaly chart above it is clear that the Antarctic sea ice has not increased because of cooling in the Antarctic region. It is clear that Antarctica is warming very quickly. The most likely reason for the small increase in Antarctic sea ice relates to stronger winds due to increased ozone. Other possible causes are increased precipitation and increased glacial run off, both caused by the warming process. See this link for some discussion of this issue. There is evidence that Antarctic sea ice was at a much higher level before the satellite era. See this link for details.
Some people make the claim that there has been little change in Global Sea Ice in the last 30 years. This claim is easily falsifiable as shown in this post.